GNAT GPL User's Guide: GNAT Project Manager

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# 11. GNAT Project Manager

> 11.1 Introduction |  |
> 11.2 Building With Projects |  |
> 11.3 Organizing Projects into Subsystems |  |
> 11.4 Scenarios in Projects |  |
> 11.5 Library Projects |  |
> 11.6 Project Extension |  |
> 11.7 Aggregate Projects |  |
> 11.8 Aggregate Library Projects |  |
> 11.9 Project File Reference |  |

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## 11.1 Introduction

This chapter describes GNAT's Project Manager, a facility that allows you to manage complex builds involving a number of source files, directories, and options for different system configurations. In particular, project files allow you to specify:

- The directory or set of directories containing the source files, and/or the names of the specific source files themselves
- The directory in which the compiler's output (``ALI'` files, object files, tree files, etc.) is to be placed
- The directory in which the executable programs are to be placed
- Switch settings for any of the project-enabled tools; you can apply these settings either globally or to individual compilation units.
- The source files containing the main subprogram(s) to be built
- The source programming language(s)
- Source file naming conventions; you can specify these either globally or for individual compilation units (see section 11.2.9 Naming Schemes).
- Change any of the above settings depending on external values, thus enabling the reuse of the projects in various scenarios (see section 11.4 Scenarios in Projects).
- Automatically build libraries as part of the build process (see section 11.5 Library Projects).

Project files are written in a syntax close to that of Ada, using familiar notions such as packages, context clauses, declarations, default values, assignments, and inheritance (see section 11.9 Project File Reference).

Project files can be built hierarchically from other project files, simplifying complex system integration and project reuse (see section 11.3 Organizing Projects into Subsystems).

- One project can import other projects containing needed source files. More generally, the Project Manager lets you structure large development efforts into hierarchical subsystems, where build decisions are delegated to the subsystem level, and thus different compilation environments (switch settings) used for different subsystems.
- You can organize GNAT projects in a hierarchy: a child project can extend a parent project, inheriting the parent's source files and optionally overriding any of them with alternative versions (see section 11.6 Project Extension).

Several tools support project files, generally in addition to specifying the information on the command line itself). They share common switches to control the loading of the project (in particular ``-Pprojectfile'` and ``-Xvbl=value'`).

The Project Manager supports a wide range of development strategies, for systems of all sizes. Here are some typical practices that are easily handled:

- Using a common set of source files and generating object files in different directories via different switch settings. It can be used for instance, for generating separate sets of object files for debugging and for production.
- Using a mostly-shared set of source files with different versions of some units or subunits. It can be used for instance, for grouping and hiding

all OS dependencies in a small number of implementation units.

Project files can be used to achieve some of the effects of a source versioning system (for example, defining separate projects for the different sets of sources that comprise different releases) but the Project Manager is independent of any source configuration management tool that might be used by the developers.

The various sections below introduce the different concepts related to projects. Each section starts with examples and use cases, and then goes into the details of related project file capabilities.

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## 11.2 Building With Projects

In its simplest form, a unique project is used to build a single executable. This section concentrates on such a simple setup. Later sections will extend this basic model to more complex setups.

The following concepts are the foundation of project files, and will be further detailed later in this documentation. They are summarized here as a reference.

Project file:
  A text file using an Ada-like syntax, generally using the ``.gpr'` extension. It defines build-related characteristics of an application. The characteristics include the list of sources, the location of those sources, the location for the generated object files, the name of the main program, and the options for the various tools involved in the build process.

Project attribute:
  A specific project characteristic is defined by an attribute clause. Its value is a string or a sequence of strings. All settings in a project are defined through a list of predefined attributes with precise semantics. See section 11.9.10 Attributes.

Package in a project:
  Global attributes are defined at the top level of a project. Attributes affecting specific tools are grouped in a package whose name is related to tool's function. The most common packages are `Builder`, `Compiler`, `Binder`, and `Linker`. See section 11.9.4 Packages.

Project variables:
  In addition to attributes, a project can use variables to store intermediate values and avoid duplication in complex expressions. It can be initialized with a value coming from the environment. A frequent use of variables is to define scenarios. See section 11.9.6 External Values, See section 11.4 Scenarios in Projects, and See section 11.9.8 Variables.

Source files and source directories:
  A source file is associated with a language through a naming convention. For instance, `foo.c` is typically the name of a C source file; `bar.ads` or `bar.1.ada` are two common naming conventions for a file containing an Ada spec. A compilation unit is often composed of a main source file and potentially several auxiliary ones, such as header files in C. The naming conventions can be user defined See section 11.2.9 Naming Schemes, and will drive the builder to call the appropriate compiler for the given source file. Source files are searched for in the source directories associated with the project through the Source_Dirs attribute. By default, all the files (in these source directories) following the naming conventions associated with the declared languages are considered to be part of the project. It is also possible to limit the list of source files using the Source_Files or Source_List_File attributes. Note that those last two attributes only accept basenames with no directory information.

Object files and object directory:
  An object file is an intermediate file produced by the compiler from a compilation unit. It is used by post-compilation tools to produce final executables or libraries. Object files produced in the context of a given project are stored in a single directory that can be specified by the Object_Dir attribute. In order to store objects in two or more object directories, the system must be split into distinct subsystems with their own project file. /first exam

The following subsections introduce gradually all the attributes of interest for simple build needs. Here is the simple setup that will be used in the following examples.

The Ada source files ``pack.ads'`, ``pack.adb'`, and ``proc.adb'` are in the ``common/'` directory. The file ``proc.adb'` contains an Ada main subprogram `Proc` that `with`s package `Pack`. We want to compile these source files with the switch ``-O2'`, and put the resulting files in the directory ``obj/'`.

    common/
      pack.ads
      pack.adb
      proc.adb
    common/release/
      proc.ali, proc.o pack.ali, pack.o

Our project is to be called Build. The name of the file is the name of the project (case-insensitive) with the ``.gpr'` extension, therefore the project file name is ``build.gpr'`. This is not mandatory, but a warning is issued when this convention is not followed.

This is a very simple example, and as stated above, a single project file is enough for it. We will thus create a new file, that for now should contain the following code:

    project Build is
    end Build;

> 11.2.1 Source Files and Directories |  |
> 11.2.2 Duplicate Sources in Projects |  |
> 11.2.3 Object and Exec Directory |  |
> 11.2.4 Main Subprograms |  |
> 11.2.5 Tools Options in Project Files |  |
> 11.2.6 Compiling with Project Files |  |
> 11.2.7 Executable File Names |  |
> 11.2.8 Avoid Duplication With Variables |  |
> 11.2.9 Naming Schemes |  |
> 11.2.10 Installation |  |
> 11.2.11 Distributed support |  |

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### 11.2.1 Source Files and Directories

When you create a new project, the first thing to describe is how to find the corresponding source files. This is the only settings that are needed by all the tools that will use this project (builder, compiler, binder and linker for the compilation, IDEs to edit the source files,...).

First step is to declare the source directories, which are the directories to be searched to find source files. In the case of the example, the ``common'` directory is the only source directory.

There are several ways of defining source directories:

- When the attribute Source_Dirs is not used, a project contains a single source directory which is the one where the project file itself resides. In our example, if ``build.gpr'` is placed in the ``common'` directory, the project has the needed implicit source directory.

- The attribute Source_Dirs can be set to a list of path names, one for each of the source directories. Such paths can either be absolute names (for instance ``"/usr/local/common/"'` on UNIX), or relative to the directory in which the project file resides (for instance "." if ``build.gpr'` is inside ``common/'`, or "common" if it is one level up). Each of the source directories must exist and be readable.

  The syntax for directories is platform specific. For portability, however, the project manager will always properly translate UNIX-like path names to the native format of specific platform. For instance, when the same project file is to be used both on Unix and Windows, "/" should be used as the directory separator rather than "\".

- The attribute Source_Dirs can automatically include subdirectories using a special syntax inspired by some UNIX shells. If any of the path in the list ends with "**", then that path and all its subdirectories (recursively) are included in the list of source directories. For instance, ``**'` and ``./**'` represent the complete directory tree rooted at ".".

  When using that construct, it can sometimes be convenient to also use the attribute Excluded_Source_Dirs, which is also a list of paths. Each entry specifies a directory whose immediate content, not including subdirs, is to be excluded. It is also possible to exclude a complete directory subtree using the "**" notation.

  It is often desirable to remove, from the source directories, directory subtrees rooted at some subdirectories. An example is the subdirectories created by a Version Control System such as Subversion that creates directory subtrees rooted at subdirectories ".svn". To do that, attribute Ignore_Source_Sub_Dirs can be used. It specifies the list of simple file names for the roots of these undesirable directory subtrees.

          for Source_Dirs use ("./**");
          for Ignore_Source_Sub_Dirs use (".svn");

When applied to the simple example, and because we generally prefer to have the project file at the toplevel directory rather than mixed with the sources, we will create the following file

       build.gpr
       project Build is
          for Source_Dirs use ("common");  --  <<<<
       end Build;

Once source directories have been specified, one may need to indicate source files of interest. By default, all source files present in the source directories are considered by the project manager. When this is not desired, it is possible to specify the list of sources to consider explicitly. In such a case, only source file base names are indicated and not their absolute or relative path names. The project manager is in charge of locating the specified source files in the specified source directories.

- By default, the project manager search for all source files of all specified languages in all the source directories.

  Since the project manager was initially developed for Ada environments, the default language is usually Ada and the above project file is complete: it defines without ambiguity the sources composing the project: that is to say, all the sources in subdirectory "common" for the default language (Ada) using the default naming convention.

  However, when compiling a multi-language application, or a pure C application, the project manager must be told which languages are of interest, which is done by setting the Languages attribute to a list of strings, each of which is the name of a language. Tools like `gnatmake` only know about Ada, while other tools like `gprbuild` know about many more languages such as C, C++, Fortran, assembly and others can be added dynamically.

  Even when using only Ada, the default naming might not be suitable. Indeed, how does the project manager recognizes an "Ada file" from any other file? Project files can describe the naming scheme used for source files, and override the default (see section 11.2.9 Naming Schemes). The default is the standard GNAT extension (``.adb'` for bodies and ``.ads'` for specs), which is what is used in our example, explaining why no naming scheme is explicitly specified. See section 11.2.9 Naming Schemes.

- `Source_Files` In some cases, source directories might contain files that should not be included in a project. One can specify the explicit list of file names to be considered through the Source_Files attribute. When this attribute is defined, instead of looking at every file in the source directories, the project manager takes only those names into consideration reports errors if they cannot be found in the source directories or does not correspond to the naming scheme.

- For various reasons, it is sometimes useful to have a project with no sources (most of the time because the attributes defined in the project file will be reused in other projects, as explained in see section 11.3 Organizing Projects into Subsystems. To do this, the attribute Source_Files is set to the empty list, i.e. `()`. Alternatively, Source_Dirs can be set to the empty list, with the same result.

- `Source_List_File` If there is a great number of files, it might be more convenient to use the attribute Source_List_File, which specifies the full path of a file. This file must contain a list of source file names (one per line, no directory information) that are searched as if they had been defined through Source_Files. Such a file can easily be created through external tools.

  A warning is issued if both attributes `Source_Files` and `Source_List_File` are given explicit values. In this case, the attribute `Source_Files` prevails.

- `Excluded_Source_Files` Specifying an explicit list of files is not always convenient.It might be more convenient to use the default search rules with specific exceptions. This can be done thanks to the attribute Excluded_Source_Files (or its synonym Locally_Removed_Files). Its value is the list of file names that should not be taken into account. This attribute is often used when extending a project, See section 11.6 Project Extension. A similar attribute Excluded_Source_List_File plays the same role but takes the name of file containing file names similarly to `Source_List_File`.

In most simple cases, such as the above example, the default source file search behavior provides the expected result, and we do not need to add anything after setting `Source_Dirs`. The project manager automatically finds ``pack.ads'`, ``pack.adb'` and ``proc.adb'` as source files of the project.

Note that by default a warning is issued when a project has no sources attached to it and this is not explicitly indicated in the project file.

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### 11.2.2 Duplicate Sources in Projects

If the order of the source directories is known statically, that is if `"/**"` is not used in the string list `Source_Dirs`, then there may be several files with the same source file name sitting in different directories of the project. In this case, only the file in the first directory is considered as a source of the project and the others are hidden. If `"/**"` is used in the string list `Source_Dirs`, it is an error to have several files with the same source file name in the same directory `"/**"` subtree, since there would be an ambiguity as to which one should be used. However, two files with the same source file name may exist in two single directories or directory subtrees. In this case, the one in the first directory or directory subtree is a source of the project.

If there are two sources in different directories of the same `"/**"` subtree, one way to resolve the problem is to exclude the directory of the file that should not be used as a source of the project.

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### 11.2.3 Object and Exec Directory

The next step when writing a project is to indicate where the compiler should put the object files. In fact, the compiler and other tools might create several different kind of files (for GNAT, there is the object file and the ALI file for instance). One of the important concepts in projects is that most tools may consider source directories as read-only and do not attempt to create new or temporary files there. Instead, all files are created in the object directory. It is of course not true for project-aware IDEs, whose purpose it is to create the source files.

The object directory is specified through the Object_Dir attribute. Its value is the path to the object directory, either absolute or relative to the directory containing the project file. This directory must already exist and be readable and writable, although some tools have a switch to create the directory if needed (See the switch `-p` for `gnatmake` and `gprbuild`).

If the attribute `Object_Dir` is not specified, it defaults to the project directory, that is the directory containing the project file.

For our example, we can specify the object dir in this way:

       project Build is
          for Source_Dirs use ("common");
          for Object_Dir use "obj";   --  <<<<
       end Build;

As mentioned earlier, there is a single object directory per project. As a result, if you have an existing system where the object files are spread in several directories, you can either move all of them into the same directory if you want to build it with a single project file, or study the section on subsystems (see section 11.3 Organizing Projects into Subsystems) to see how each separate object directory can be associated with one of the subsystem constituting the application.

When the `linker` is called, it usually creates an executable. By default, this executable is placed in the object directory of the project. It might be convenient to store it in its own directory.

This can be done through the `Exec_Dir` attribute, which, like Object_Dir contains a single absolute or relative path and must point to an existing and writable directory, unless you ask the tool to create it on your behalf. When not specified, It defaults to the object directory and therefore to the project file's directory if neither Object_Dir nor Exec_Dir was specified.

In the case of the example, let's place the executable in the root of the hierarchy, ie the same directory as ``build.gpr'`. Hence the project file is now

       project Build is
          for Source_Dirs use ("common");
          for Object_Dir use "obj";
          for Exec_Dir use ".";  --   <<<<
       end Build;

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### 11.2.4 Main Subprograms

In the previous section, executables were mentioned. The project manager needs to be taught what they are. In a project file, an executable is indicated by pointing to source file of the main subprogram. In C this is the file that contains the `main` function, and in Ada the file that contains the main unit.

There can be any number of such main files within a given project, and thus several executables can be built in the context of a single project file. Of course, one given executable might not (and in fact will not) need all the source files referenced by the project. As opposed to other build environments such as `makefile`, one does not need to specify the list of dependencies of each executable, the project-aware builders knows enough of the semantics of the languages to build ands link only the necessary elements.

The list of main files is specified via the Main attribute. It contains a list of file names (no directories). If a project defines this attribute, it is not necessary to identify main files on the command line when invoking a builder, and editors like `GPS` will be able to create extra menus to spawn or debug the corresponding executables.

       project Build is
          for Source_Dirs use ("common");
          for Object_Dir use "obj";
          for Exec_Dir use ".";
          for Main use ("proc.adb");  --   <<<<
       end Build;

If this attribute is defined in the project, then spawning the builder with a command such as

       gnatmake -Pbuild

automatically builds all the executables corresponding to the files listed in the Main attribute. It is possible to specify one or more executables on the command line to build a subset of them.

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### 11.2.5 Tools Options in Project Files

We now have a project file that fully describes our environment, and can be used to build the application with a simple `gnatmake` command as seen in the previous section. In fact, the empty project we showed immediately at the beginning (with no attribute at all) could already fulfill that need if it was put in the ``common'` directory.

Of course, we always want more control. This section will show you how to specify the compilation switches that the various tools involved in the building of the executable should use.

Since source names and locations are described into the project file, it is not necessary to use switches on the command line for this purpose (switches such as -I for gcc). This removes a major source of command line length overflow. Clearly, the builders will have to communicate this information one way or another to the underlying compilers and tools they call but they usually use response files for this and thus should not be subject to command line overflows.

Several tools are participating to the creation of an executable: the compiler produces object files from the source files; the binder (in the Ada case) creates an source file that takes care, among other things, of elaboration issues and global variables initialization; and the linker gathers everything into a single executable that users can execute. All these tools are known by the project manager and will be called with user defined switches from the project files. However, we need to introduce a new project file concept to express which switches to be used for any of the tools involved in the build.

A project file is subdivided into zero or more packages, each of which contains the attributes specific to one tool (or one set of tools). Project files use an Ada-like syntax for packages. Package names permitted in project files are restricted to a predefined set (see section 11.9.4 Packages), and the contents of packages are limited to a small set of constructs and attributes (see section 11.9.10 Attributes).

Our example project file can be extended with the following empty packages. At this stage, they could all be omitted since they are empty, but they show which packages would be involved in the build process.

       project Build is
          for Source_Dirs use ("common");
          for Object_Dir use "obj";
          for Exec_Dir use ".";
          for Main use ("proc.adb");

          package Builder is  --<<<  for gnatmake and gprbuild
          end Builder;

          package Compiler is --<<<  for the compiler
          end Compiler;

          package Binder is   --<<<  for the binder
          end Binder;

          package Linker is   --<<<  for the linker
          end Linker;
       end Build;

Let's first examine the compiler switches. As stated in the initial description of the example, we want to compile all files with ``-O2'`. This is a compiler switch, although it is usual, on the command line, to pass it to the builder which then passes it to the compiler. It is recommended to use directly the right package, which will make the setup easier to understand for other people.

Several attributes can be used to specify the switches:

Default_Switches:
  This is the first mention in this manual of an indexed attribute. When this attribute is defined, one must supply an index in the form of a literal string. In the case of Default_Switches, the index is the name of the language to which the switches apply (since a different compiler will likely be used for each language, and each compiler has its own set of switches). The value of the attribute is a list of switches.

  In this example, we want to compile all Ada source files with the switch ``-O2'`, and the resulting project file is as follows (only the `Compiler` package is shown):

        package Compiler is
          for Default_Switches ("Ada") use ("-O2");
        end Compiler;

Switches:
  in some cases, we might want to use specific switches for one or more files. For instance, compiling ``proc.adb'` might not be possible at high level of optimization because of a compiler issue. In such a case, the Switches attribute (indexed on the file name) can be used and will override the switches defined by Default_Switches. Our project file would become:

        package Compiler is
           for Default_Switches ("Ada")
               use ("-O2");
           for Switches ("proc.adb")
               use ("-O0");
        end Compiler;

  `Switches` may take a pattern as an index, such as in:

        package Compiler is
          for Default_Switches ("Ada")
              use ("-O2");
          for Switches ("pkg*")
              use ("-O0");
        end Compiler;

  Sources ``pkg.adb'` and ``pkg-child.adb'` would be compiled with -O0, not -O2.

  `Switches` can also be given a language name as index instead of a file name in which case it has the same semantics as Default_Switches. However, indexes with wild cards are never valid for language name.

Local_Configuration_Pragmas:
  this attribute may specify the path of a file containing configuration pragmas for use by the Ada compiler, such as `pragma Restrictions (No_Tasking)`. These pragmas will be used for all the sources of the project.

The switches for the other tools are defined in a similar manner through the Default_Switches and Switches attributes, respectively in the Builder package (for `gnatmake` and `gprbuild`), the Binder package (binding Ada executables) and the Linker package (for linking executables).

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### 11.2.6 Compiling with Project Files

Now that our project files are written, let's build our executable. Here is the command we would use from the command line:

       gnatmake -Pbuild

This will automatically build the executables specified through the Main attribute: for each, it will compile or recompile the sources for which the object file does not exist or is not up-to-date; it will then run the binder; and finally run the linker to create the executable itself.

`gnatmake` only knows how to handle Ada files. By using `gprbuild` as a builder, you could automatically manage C files the same way: create the file ``utils.c'` in the ``common'` directory, set the attribute Languages to `"(Ada, C)"`, and run

       gprbuild -Pbuild

Gprbuild knows how to recompile the C files and will recompile them only if one of their dependencies has changed. No direct indication on how to build the various elements is given in the project file, which describes the project properties rather than a set of actions to be executed. Here is the invocation of `gprbuild` when building a multi-language program:

    $ gprbuild -Pbuild
    gcc -c proc.adb
    gcc -c pack.adb
    gcc -c utils.c
    gprbind proc
    ...
    gcc proc.o -o proc

Notice the three steps described earlier:

- The first three gcc commands correspond to the compilation phase.
- The gprbind command corresponds to the post-compilation phase.
- The last gcc command corresponds to the final link.

The default output of GPRbuild's execution is kept reasonably simple and easy to understand. In particular, some of the less frequently used commands are not shown, and some parameters are abbreviated. So it is not possible to rerun the effect of the `gprbuild` command by cut-and-pasting its output. GPRbuild's option `-v` provides a much more verbose output which includes, among other information, more complete compilation, post-compilation and link commands.

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### 11.2.7 Executable File Names

By default, the executable name corresponding to a main file is computed from the main source file name. Through the attribute Builder.Executable, it is possible to change this default.

For instance, instead of building `proc` (or `proc.exe` on Windows), we could configure our project file to build "proc1" (resp proc1.exe) with the following addition:

       project Build is
          ...  --  same as before
          package Builder is
             for Executable ("proc.adb") use "proc1";
          end Builder
       end Build;

Attribute Executable_Suffix, when specified, may change the suffix of the executable files, when no attribute `Executable` applies: its value replace the platform-specific executable suffix. The default executable suffix is empty on UNIX and ".exe" on Windows.

It is also possible to change the name of the produced executable by using the command line switch ``-o'`. When several mains are defined in the project, it is not possible to use the ``-o'` switch and the only way to change the names of the executable is provided by Attributes `Executable` and `Executable_Suffix`.

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### 11.2.8 Avoid Duplication With Variables

To illustrate some other project capabilities, here is a slightly more complex project using similar sources and a main program in C:

    project C_Main is
       for Languages    use ("Ada", "C");
       for Source_Dirs  use ("common");
       for Object_Dir   use  "obj";
       for Main         use ("main.c");
       package Compiler is
          C_Switches := ("-pedantic");
          for Default_Switches ("C")   use C_Switches;
          for Default_Switches ("Ada") use ("-gnaty");
          for Switches ("main.c") use C_Switches & ("-g");
       end Compiler;
    end C_Main;

This project has many similarities with the previous one. As expected, its `Main` attribute now refers to a C source. The attribute Exec_Dir is now omitted, thus the resulting executable will be put in the directory ``obj'`.

The most noticeable difference is the use of a variable in the Compiler package to store settings used in several attributes. This avoids text duplication, and eases maintenance (a single place to modify if we want to add new switches for C files). We will revisit the use of variables in the context of scenarios (see section 11.4 Scenarios in Projects).

In this example, we see how the file ``main.c'` can be compiled with the switches used for all the other C files, plus ``-g'`. In this specific situation the use of a variable could have been replaced by a reference to the `Default_Switches` attribute:

       for Switches ("c_main.c") use Compiler'Default_Switches ("C") & ("-g");

Note the tick (') used to refer to attributes defined in a package.

Here is the output of the GPRbuild command using this project:

    $gprbuild -Pc_main
    gcc -c -pedantic -g main.c
    gcc -c -gnaty proc.adb
    gcc -c -gnaty pack.adb
    gcc -c -pedantic utils.c
    gprbind main.bexch
    ...
    gcc main.o -o main

The default switches for Ada sources, the default switches for C sources (in the compilation of ``lib.c'`), and the specific switches for ``main.c'` have all been taken into account.

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### 11.2.9 Naming Schemes

Sometimes an Ada software system is ported from one compilation environment to another (say GNAT), and the file are not named using the default GNAT conventions. Instead of changing all the file names, which for a variety of reasons might not be possible, you can define the relevant file naming scheme in the Naming package of your project file.

The naming scheme has two distinct goals for the project manager: it allows finding of source files when searching in the source directories, and given a source file name it makes it possible to guess the associated language, and thus the compiler to use.

Note that the use by the Ada compiler of pragmas Source_File_Name is not supported when using project files. You must use the features described in this paragraph. You can however specify other configuration pragmas.

The following attributes can be defined in package `Naming`:

Casing:
  Its value must be one of `"lowercase"` (the default if unspecified), `"uppercase"` or `"mixedcase"`. It describes the casing of file names with regards to the Ada unit name. Given an Ada unit My_Unit, the file name will respectively be ``my_unit.adb'` (lowercase), ``MY_UNIT.ADB'` (uppercase) or ``My_Unit.adb'` (mixedcase). On Windows, file names are case insensitive, so this attribute is irrelevant.

Dot_Replacement:
  This attribute specifies the string that should replace the "." in unit names. Its default value is `"-"` so that a unit `Parent.Child` is expected to be found in the file ``parent-child.adb'`. The replacement string must satisfy the following requirements to avoid ambiguities in the naming scheme:

  - It must not be empty
  - It cannot start or end with an alphanumeric character
  - It cannot be a single underscore
  - It cannot start with an underscore followed by an alphanumeric
  - It cannot contain a dot `'.'` except if the entire string is `"."`

Spec_Suffix and Specification_Suffix:
  For Ada, these attributes give the suffix used in file names that contain specifications. For other languages, they give the extension for files that contain declaration (header files in C for instance). The attribute is indexed on the language. The two attributes are equivalent, but the latter is obsolescent.

  If the value of the attribute is the empty string, it indicates to the Project Manager that the only specifications/header files for the language are those specified with attributes `Spec` or `Specification_Exceptions`.

  If `Spec_Suffix ("Ada")` is not specified, then the default is `".ads"`.

  A non empty value must satisfy the following requirements:

  - It must include at least one dot
  - If `Dot_Replacement` is a single dot, then it cannot include more than one dot.

Body_Suffix and Implementation_Suffix:
  These attributes give the extension used for file names that contain code (bodies in Ada). They are indexed on the language. The second version is obsolescent and fully replaced by the first attribute.

  For each language of a project, one of these two attributes need to be specified, either in the project itself or in the configuration project file.

  If the value of the attribute is the empty string, it indicates to the Project Manager that the only source files for the language are those specified with attributes `Body` or `Implementation_Exceptions`.

  These attributes must satisfy the same requirements as `Spec_Suffix`. In addition, they must be different from any of the values in `Spec_Suffix`. If `Body_Suffix ("Ada")` is not specified, then the default is `".adb"`.

  If `Body_Suffix ("Ada")` and `Spec_Suffix ("Ada")` end with the same string, then a file name that ends with the longest of these two suffixes will be a body if the longest suffix is `Body_Suffix ("Ada")` or a spec if the longest suffix is `Spec_Suffix ("Ada")`.

  If the suffix does not start with a '.', a file with a name exactly equal to the suffix will also be part of the project (for instance if you define the suffix as `Makefile.in`, a file called ``Makefile.in'` will be part of the project. This capability is usually not interesting when building. However, it might become useful when a project is also used to find the list of source files in an editor, like the GNAT Programming System (GPS).

Separate_Suffix:
  This attribute is specific to Ada. It denotes the suffix used in file names that contain separate bodies. If it is not specified, then it defaults to same value as `Body_Suffix ("Ada")`.

  The value of this attribute cannot be the empty string.

  Otherwise, the same rules apply as for the `Body_Suffix` attribute. The only accepted index is "Ada".

Spec or Specification:
  This attribute `Spec` can be used to define the source file name for a given Ada compilation unit's spec. The index is the literal name of the Ada unit (case insensitive). The value is the literal base name of the file that contains this unit's spec (case sensitive or insensitive depending on the operating system). This attribute allows the definition of exceptions to the general naming scheme, in case some files do not follow the usual convention.

  When a source file contains several units, the relative position of the unit can be indicated. The first unit in the file is at position 1

         for Spec ("MyPack.MyChild") use "mypack.mychild.spec";
         for Spec ("top") use "foo.a" at 1;
         for Spec ("foo") use "foo.a" at 2;

Body or Implementation:
  These attribute play the same role as Spec for Ada bodies.

Specification_Exceptions and Implementation_Exceptions:
  These attributes define exceptions to the naming scheme for languages other than Ada. They are indexed on the language name, and contain a list of file names respectively for headers and source code.

For example, the following package models the Apex file naming rules:

      package Naming is
        for Casing               use "lowercase";
        for Dot_Replacement      use ".";
        for Spec_Suffix ("Ada")  use ".1.ada";
        for Body_Suffix ("Ada")  use ".2.ada";
      end Naming;

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### 11.2.10 Installation

After building an application or a library it is often required to install it into the development environment. For instance this step is required if the library is to be used by another application. The `gprinstall` tool provides an easy way to install libraries, executable or object code generated during the build. The Install package can be used to change the default locations.

The following attributes can be defined in package `Install`:

Active

  Whether the project is to be installed, values are `true` (default) or `false`.

Artifacts

  An array attribute to declare a set of files not part of the sources to be installed. The array discriminant is the directory where the file is to be installed. If a relative directory then Prefix (see below) is prepended.

Prefix:

  Root directory for the installation.

Exec_Subdir

  Subdirectory of Prefix where executables are to be installed. Default is bin.

Lib_Subdir

  Subdirectory of Prefix where directory with the library or object files is to be installed. Default is lib.

Sources_Subdir

  Subdirectory of Prefix where directory with sources is to be installed. Default is include.

Project_Subdir

  Subdirectory of Prefix where the generated project file is to be installed. Default is share/gpr.

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### 11.2.11 Distributed support

For large projects the compilation time can become a limitation in the development cycle. To cope with that, GPRbuild supports distributed compilation.

The following attributes can be defined in package `Remote`:

Root_Dir:

  Root directory of the project's sources. The default value is the project's directory.

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## 11.3 Organizing Projects into Subsystems

A subsystem is a coherent part of the complete system to be built. It is represented by a set of sources and one single object directory. A system can be composed of a single subsystem when it is simple as we have seen in the first section. Complex systems are usually composed of several interdependent subsystems. A subsystem is dependent on another subsystem if knowledge of the other one is required to build it, and in particular if visibility on some of the sources of this other subsystem is required. Each subsystem is usually represented by its own project file.

In this section, the previous example is being extended. Let's assume some sources of our `Build` project depend on other sources. For instance, when building a graphical interface, it is usual to depend upon a graphical library toolkit such as GtkAda. Furthermore, we also need sources from a logging module we had previously written.

> 11.3.1 Project Dependencies |  |
> 11.3.2 Cyclic Project Dependencies |  |
> 11.3.3 Sharing Between Projects |  |
> 11.3.4 Global Attributes |  |

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### 11.3.1 Project Dependencies

GtkAda comes with its own project file (appropriately called ``gtkada.gpr'`), and we will assume we have already built a project called ``logging.gpr'` for the logging module. With the information provided so far in ``build.gpr'`, building the application would fail with an error indicating that the gtkada and logging units that are relied upon by the sources of this project cannot be found.

This is easily solved by adding the following with clauses at the beginning of our project:

      with "gtkada.gpr";
      with "a/b/logging.gpr";
      project Build is
         ...  --  as before
      end Build;

When such a project is compiled, `gnatmake` will automatically check the other projects and recompile their sources when needed. It will also recompile the sources from `Build` when needed, and finally create the executable. In some cases, the implementation units needed to recompile a project are not available, or come from some third-party and you do not want to recompile it yourself. In this case, the attribute Externally_Built to "true" can be set, indicating to the builder that this project can be assumed to be up-to-date, and should not be considered for recompilation. In Ada, if the sources of this externally built project were compiled with another version of the compiler or with incompatible options, the binder will issue an error.

The project's `with` clause has several effects. It provides source visibility between projects during the compilation process. It also guarantees that the necessary object files from `Logging` and `GtkAda` are available when linking `Build`.

As can be seen in this example, the syntax for importing projects is similar to the syntax for importing compilation units in Ada. However, project files use literal strings instead of names, and the `with` clause identifies project files rather than packages.

Each literal string after `with` is the path (absolute or relative) to a project file. The `.gpr` extension is optional, although we recommend adding it. If no extension is specified, and no project file with the ``.gpr'` extension is found, then the file is searched for exactly as written in the `with` clause, that is with no extension.

As mentioned above, the path after a `with` has to be a literal string, and you cannot use concatenation, or lookup the value of external variables to change the directories from which a project is loaded. A solution if you need something like this is to use aggregate projects (see section 11.7 Aggregate Projects).

When a relative path or a base name is used, the project files are searched relative to each of the directories in the project path. This path includes all the directories found with the following algorithm, in that order, as soon as a matching file is found, the search stops:

- First, the file is searched relative to the directory that contains the current project file.

- Then it is searched relative to all the directories specified in the environment variables GPR_PROJECT_PATH_FILE, GPR_PROJECT_PATH and ADA_PROJECT_PATH (in that order) if they exist. The value of GPR_PROJECT_PATH_FILE, when defined, is the path name of a text file that contains project directory path names, one per line. GPR_PROJECT_PATH and ADA_PROJECT_PATH, when defined, contain project directory path names separated by directory separators. ADA_PROJECT_PATH is used for compatibility, it is recommended to use GPR_PROJECT_PATH_FILE or GPR_PROJECT_PATH.

- Finally, it is searched relative to the default project directories. Such directories depends on the tool used. The different locations searched in the specified order are:

  - ``<prefix>/<target>/lib/gnat'` (for `gnatmake` in all cases, and for `gprbuild` if option ``--target'` is specified)
  - ``<prefix>/<target>/share/gpr'` (for `gnatmake` in all cases, and for `gprbuild` if option ``--target'` is specified)
  - ``<prefix>/share/gpr/'` (for `gnatmake` and `gprbuild`)
  - ``<prefix>/lib/gnat/'` (for `gnatmake` and `gprbuild`)

  In our example, ``gtkada.gpr'` is found in the predefined directory if it was installed at the same root as GNAT.

Some tools also support extending the project path from the command line, generally through the ``-aP'`. You can see the value of the project path by using the `gnatls -v` command.

Any symbolic link will be fully resolved in the directory of the importing project file before the imported project file is examined.

Any source file in the imported project can be used by the sources of the importing project, transitively. Thus if `A` imports `B`, which imports `C`, the sources of `A` may depend on the sources of `C`, even if `A` does not import `C` explicitly. However, this is not recommended, because if and when `B` ceases to import `C`, some sources in `A` will no longer compile. `gprbuild` has a switch ``--no-indirect-imports'` that will report such indirect dependencies.

One very important aspect of a project hierarchy is that a given source can only belong to one project (otherwise the project manager would not know which settings apply to it and when to recompile it). It means that different project files do not usually share source directories or when they do, they need to specify precisely which project owns which sources using attribute `Source_Files` or equivalent. By contrast, 2 projects can each own a source with the same base file name as long as they live in different directories. The latter is not true for Ada Sources because of the correlation between source files and Ada units.

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### 11.3.2 Cyclic Project Dependencies

Cyclic dependencies are mostly forbidden: if `A` imports `B` (directly or indirectly) then `B` is not allowed to import `A`. However, there are cases when cyclic dependencies would be beneficial. For these cases, another form of import between projects exists: the limited with. A project `A` that imports a project `B` with a straight `with` may also be imported, directly or indirectly, by `B` through a `limited with`.

The difference between straight `with` and `limited with` is that the name of a project imported with a `limited with` cannot be used in the project importing it. In particular, its packages cannot be renamed and its variables cannot be referred to.

    with "b.gpr";
    with "c.gpr";
    project A is
        For Exec_Dir use B'Exec_Dir; -- ok
    end A;

    limited with "a.gpr";   --  Cyclic dependency: A -> B -> A
    project B is
       For Exec_Dir use A'Exec_Dir; -- not ok
    end B;

    with "d.gpr";
    project C is
    end C;

    limited with "a.gpr";  --  Cyclic dependency: A -> C -> D -> A
    project D is
       For Exec_Dir use A'Exec_Dir; -- not ok
    end D;

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### 11.3.3 Sharing Between Projects

When building an application, it is common to have similar needs in several of the projects corresponding to the subsystems under construction. For instance, they will all have the same compilation switches.

As seen before (see section 11.2.5 Tools Options in Project Files), setting compilation switches for all sources of a subsystem is simple: it is just a matter of adding a `Compiler.Default_Switches` attribute to each project files with the same value. Of course, that means duplication of data, and both places need to be changed in order to recompile the whole application with different switches. It can become a real problem if there are many subsystems and thus many project files to edit.

There are two main approaches to avoiding this duplication:

- Since ``build.gpr'` imports ``logging.gpr'`, we could change it to reference the attribute in Logging, either through a package renaming, or by referencing the attribute. The following example shows both cases:

        project Logging is
           package Compiler is
              for Switches ("Ada")
                  use ("-O2");
           end Compiler;
           package Binder is
              for Switches ("Ada")
                  use ("-E");
           end Binder;
        end Logging;

        with "logging.gpr";
        project Build is
           package Compiler renames Logging.Compiler;
           package Binder is
              for Switches ("Ada") use Logging.Binder'Switches ("Ada");
           end Binder;
        end Build;

  The solution used for `Compiler` gets the same value for all attributes of the package, but you cannot modify anything from the package (adding extra switches or some exceptions). The second version is more flexible, but more verbose.

  If you need to refer to the value of a variable in an imported project, rather than an attribute, the syntax is similar but uses a "." rather than an apostrophe. For instance:

        with "imported";
        project Main is
           Var1 := Imported.Var;
        end Main;

- The second approach is to define the switches in a third project. That project is setup without any sources (so that, as opposed to the first example, none of the project plays a special role), and will only be used to define the attributes. Such a project is typically called ``shared.gpr'`.

        abstract project Shared is
           for Source_Files use ();   --  no sources
           package Compiler is
              for Switches ("Ada")
                  use ("-O2");
           end Compiler;
        end Shared;

        with "shared.gpr";
        project Logging is
           package Compiler renames Shared.Compiler;
        end Logging;

        with "shared.gpr";
        project Build is
           package Compiler renames Shared.Compiler;
        end Build;

  As for the first example, we could have chosen to set the attributes one by one rather than to rename a package. The reason we explicitly indicate that `Shared` has no sources is so that it can be created in any directory and we are sure it shares no sources with `Build` or `Logging`, which of course would be invalid.

  Note the additional use of the abstract qualifier in ``shared.gpr'`. This qualifier is optional, but helps convey the message that we do not intend this project to have sources (see section 11.9.2 Qualified Projects for more qualifiers).

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### 11.3.4 Global Attributes

We have already seen many examples of attributes used to specify a special option of one of the tools involved in the build process. Most of those attributes are project specific. That it to say, they only affect the invocation of tools on the sources of the project where they are defined.

There are a few additional attributes that apply to all projects in a hierarchy as long as they are defined on the "main" project. The main project is the project explicitly mentioned on the command-line. The project hierarchy is the "with"-closure of the main project.

Here is a list of commonly used global attributes:

Builder.Global_Configuration_Pragmas:
  This attribute points to a file that contains configuration pragmas to use when building executables. These pragmas apply for all executables built from this project hierarchy. As we have seen before, additional pragmas can be specified on a per-project basis by setting the `Compiler.Local_Configuration_Pragmas` attribute.

Builder.Global_Compilation_Switches:
  This attribute is a list of compiler switches to use when compiling any source file in the project hierarchy. These switches are used in addition to the ones defined in the `Compiler` package, which only apply to the sources of the corresponding project. This attribute is indexed on the name of the language.

Using such global capabilities is convenient. It can also lead to unexpected behavior. Especially when several subsystems are shared among different main projects and the different global attributes are not compatible. Note that using aggregate projects can be a safer and more powerful replacement to global attributes.

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## 11.4 Scenarios in Projects

Various aspects of the projects can be modified based on scenarios. These are user-defined modes that change the behavior of a project. Typical examples are the setup of platform-specific compiler options, or the use of a debug and a release mode (the former would activate the generation of debug information, when the second will focus on improving code optimization).

Let's enhance our example to support a debug and a release modes.The issue is to let the user choose what kind of system he is building: use ``-g'` as compiler switches in debug mode and ``-O2'` in release mode. We will also setup the projects so that we do not share the same object directory in both modes, otherwise switching from one to the other might trigger more recompilations than needed or mix objects from the 2 modes.

One naive approach is to create two different project files, say ``build_debug.gpr'` and ``build_release.gpr'`, that set the appropriate attributes as explained in previous sections. This solution does not scale well, because in presence of multiple projects depending on each other, you will also have to duplicate the complete hierarchy and adapt the project files to point to the right copies.

Instead, project files support the notion of scenarios controlled by external values. Such values can come from several sources (in decreasing order of priority):

Command line:
  When launching `gnatmake` or `gprbuild`, the user can pass extra ``-X'` switches to define the external value. In our case, the command line might look like

             gnatmake -Pbuild.gpr -Xmode=debug
         or  gnatmake -Pbuild.gpr -Xmode=release

Environment variables:
  When the external value does not come from the command line, it can come from the value of environment variables of the appropriate name. In our case, if an environment variable called "mode" exist, its value will be taken into account.

External function second parameter

We now need to get that value in the project. The general form is to use the predefined function external which returns the current value of the external. For instance, we could setup the object directory to point to either ``obj/debug'` or ``obj/release'` by changing our project to

       project Build is
           for Object_Dir use "obj/" & external ("mode", "debug");
           ... --  as before
       end Build;

The second parameter to `external` is optional, and is the default value to use if "mode" is not set from the command line or the environment.

In order to set the switches according to the different scenarios, other constructs have to be introduced such as typed variables and case constructions.

A typed variable is a variable that can take only a limited number of values, similar to an enumeration in Ada. Such a variable can then be used in a case construction and create conditional sections in the project. The following example shows how this can be done:

       project Build is
          type Mode_Type is ("debug", "release");  --  all possible values
          Mode : Mode_Type := external ("mode", "debug"); -- a typed variable

          package Compiler is
             case Mode is
                when "debug" =>
                   for Switches ("Ada")
                       use ("-g");
                when "release" =>
                   for Switches ("Ada")
                       use ("-O2");
             end case;
          end Compiler;
       end Build;

The project has suddenly grown in size, but has become much more flexible. `Mode_Type` defines the only valid values for the `mode` variable. If any other value is read from the environment, an error is reported and the project is considered as invalid.

The `Mode` variable is initialized with an external value defaulting to `"debug"`. This default could be omitted and that would force the user to define the value. Finally, we can use a case construction to set the switches depending on the scenario the user has chosen.

Most aspects of the projects can depend on scenarios. The notable exception are project dependencies (`with` clauses), which may not depend on a scenario.

Scenarios work the same way with project hierarchies: you can either duplicate a variable similar to `Mode` in each of the project (as long as the first argument to `external` is always the same and the type is the same), or simply set the variable in the ``shared.gpr'` project (see section 11.3.3 Sharing Between Projects).

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## 11.5 Library Projects

So far, we have seen examples of projects that create executables. However, it is also possible to create libraries instead. A library is a specific type of subsystem where, for convenience, objects are grouped together using system-specific means such as archives or windows DLLs.

Library projects provide a system- and language-independent way of building both static and dynamic libraries. They also support the concept of standalone libraries (SAL) which offers two significant properties: the elaboration (e.g. initialization) of the library is either automatic or very simple; a change in the implementation part of the library implies minimal post-compilation actions on the complete system and potentially no action at all for the rest of the system in the case of dynamic SALs.

There is a restriction on shared library projects: by default, they are only allowed to import other shared library projects. They are not allowed to import non library projects or static library projects.

The GNAT Project Manager takes complete care of the library build, rebuild and installation tasks, including recompilation of the source files for which objects do not exist or are not up to date, assembly of the library archive, and installation of the library (i.e., copying associated source, object and ``ALI'` files to the specified location).

> 11.5.1 Building Libraries |  |
> 11.5.2 Using Library Projects |  |
> 11.5.3 Stand-alone Library Projects |  |
> 11.5.4 Installing a library with project files |  |

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### 11.5.1 Building Libraries

Let's enhance our example and transform the `logging` subsystem into a library. In order to do so, a few changes need to be made to ``logging.gpr'`. A number of specific attributes needs to be defined: at least `Library_Name` and `Library_Dir`; in addition, a number of other attributes can be used to specify specific aspects of the library. For readability, it is also recommended (although not mandatory), to use the qualifier `library` in front of the `project` keyword.

Library_Name:
  This attribute is the name of the library to be built. There is no restriction on the name of a library imposed by the project manager, except for stand-alone libraries whose names must follow the syntax of Ada identifiers; however, there may be system specific restrictions on the name. In general, it is recommended to stick to alphanumeric characters (and possibly single underscores) to help portability.

Library_Dir:
  This attribute is the path (absolute or relative) of the directory where the library is to be installed. In the process of building a library, the sources are compiled, the object files end up in the explicit or implicit `Object_Dir` directory. When all sources of a library are compiled, some of the compilation artifacts, including the library itself, are copied to the library_dir directory. This directory must exists and be writable. It must also be different from the object directory so that cleanup activities in the Library_Dir do not affect recompilation needs.

Here is the new version of ``logging.gpr'` that makes it a library:

    library project Logging is          --  "library" is optional
       for Library_Name use "logging";  --  will create "liblogging.a" on Unix
       for Object_Dir   use "obj";
       for Library_Dir  use "lib";      --  different from object_dir
    end Logging;

Once the above two attributes are defined, the library project is valid and is enough for building a library with default characteristics. Other library-related attributes can be used to change the defaults:

Library_Kind:
  The value of this attribute must be either `"static"`, `"dynamic"` or `"relocatable"` (the latter is a synonym for dynamic). It indicates which kind of library should be built (the default is to build a static library, that is an archive of object files that can potentially be linked into a static executable). When the library is set to be dynamic, a separate image is created that will be loaded independently, usually at the start of the main program execution. Support for dynamic libraries is very platform specific, for instance on Windows it takes the form of a DLL while on GNU/Linux, it is a dynamic elf image whose suffix is usually ``.so'`. Library project files, on the other hand, can be written in a platform independent way so that the same project file can be used to build a library on different operating systems.

  If you need to build both a static and a dynamic library, it is recommended use two different object directories, since in some cases some extra code needs to be generated for the latter. For such cases, one can either define two different project files, or a single one which uses scenarios to indicate the various kinds of library to be built and their corresponding object_dir.

Library_ALI_Dir:
  This attribute may be specified to indicate the directory where the ALI files of the library are installed. By default, they are copied into the `Library_Dir` directory, but as for the executables where we have a separate `Exec_Dir` attribute, you might want to put them in a separate directory since there can be hundreds of them. The same restrictions as for the `Library_Dir` attribute apply.

Library_Version:
  This attribute is platform dependent, and has no effect on VMS and Windows. On Unix, it is used only for dynamic libraries as the internal name of the library (the `"soname"`). If the library file name (built from the `Library_Name`) is different from the `Library_Version`, then the library file will be a symbolic link to the actual file whose name will be `Library_Version`. This follows the usual installation schemes for dynamic libraries on many Unix systems.

        project Logging is
           Version := "1";
           for Library_Dir use "lib";
           for Library_Name use "logging";
           for Library_Kind use "dynamic";
           for Library_Version use "liblogging.so." & Version;
        end Logging;

  After the compilation, the directory ``lib'` will contain both a ``libdummy.so.1'` library and a symbolic link to it called ``libdummy.so'`.

Library_GCC:
  This attribute is the name of the tool to use instead of "gcc" to link shared libraries. A common use of this attribute is to define a wrapper script that accomplishes specific actions before calling gcc (which itself is calling the linker to build the library image).

Library_Options:
  This attribute may be used to specify additional switches (last switches) when linking a shared library.

Leading_Library_Options:
  This attribute, that is taken into account only by `gprbuild`, may be used to specified leading options (first switches) when linking a shared library.

Linker.Linker_Options:
  This attribute specifies additional switches to be given to the linker when linking an executable. It is ignored when defined in the main project and taken into account in all other projects that are imported directly or indirectly. These switches complement the `Linker.Switches` defined in the main project. This is useful when a particular subsystem depends on an external library: adding this dependency as a `Linker_Options` in the project of the subsystem is more convenient than adding it to all the `Linker.Switches` of the main projects that depend upon this subsystem.

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### 11.5.2 Using Library Projects

When the builder detects that a project file is a library project file, it recompiles all sources of the project that need recompilation and rebuild the library if any of the sources have been recompiled. It then groups all object files into a single file, which is a shared or a static library. This library can later on be linked with multiple executables. Note that the use of shard libraries reduces the size of the final executable and can also reduce the memory footprint at execution time when the library is shared among several executables.

It is also possible to build multi-language libraries. When using `gprbuild` as a builder, multi-language library projects allow naturally the creation of multi-language libraries . `gnatmake`, does not try to compile non Ada sources. However, when the project is multi-language, it will automatically link all object files found in the object directory, whether or not they were compiled from an Ada source file. This specific behavior does not apply to Ada-only projects which only take into account the objects corresponding to the sources of the project.

A non-library project can import a library project. When the builder is invoked on the former, the library of the latter is only rebuilt when absolutely necessary. For instance, if a unit of the library is not up-to-date but non of the executables need this unit, then the unit is not recompiled and the library is not reassembled. For instance, let's assume in our example that logging has the following sources: ``log1.ads'`, ``log1.adb'`, ``log2.ads'` and ``log2.adb'`. If ``log1.adb'` has been modified, then the library ``liblogging'` will be rebuilt when compiling all the sources of `Build` only if ``proc.ads'`, ``pack.ads'` or ``pack.adb'` include a `"with Log1"`.

To ensure that all the sources in the `Logging` library are up to date, and that all the sources of `Build` are also up to date, the following two commands needs to be used:

    gnatmake -Plogging.gpr
    gnatmake -Pbuild.gpr

All ``ALI'` files will also be copied from the object directory to the library directory. To build executables, `gnatmake` will use the library rather than the individual object files.

Library projects can also be useful to describe a library that need to be used but, for some reason, cannot be rebuilt. For instance, it is the case when some of the library sources are not available. Such library projects need simply to use the `Externally_Built` attribute as in the example below:

    library project Extern_Lib is
       for Languages    use ("Ada", "C");
       for Source_Dirs  use ("lib_src");
       for Library_Dir  use "lib2";
       for Library_Kind use "dynamic";
       for Library_Name use "l2";
       for Externally_Built use "true";  --  <<<<
    end Extern_Lib;

In the case of externally built libraries, the `Object_Dir` attribute does not need to be specified because it will never be used.

The main effect of using such an externally built library project is mostly to affect the linker command in order to reference the desired library. It can also be achieved by using `Linker.Linker_Options` or `Linker.Switches` in the project corresponding to the subsystem needing this external library. This latter method is more straightforward in simple cases but when several subsystems depend upon the same external library, finding the proper place for the `Linker.Linker_Options` might not be easy and if it is not placed properly, the final link command is likely to present ordering issues. In such a situation, it is better to use the externally built library project so that all other subsystems depending on it can declare this dependency thanks to a project `with` clause, which in turn will trigger the builder to find the proper order of libraries in the final link command.

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### 11.5.3 Stand-alone Library Projects

A stand-alone library is a library that contains the necessary code to elaborate the Ada units that are included in the library. A stand-alone library is a convenient way to add an Ada subsystem to a more global system whose main is not in Ada since it makes the elaboration of the Ada part mostly transparent. However, stand-alone libraries are also useful when the main is in Ada: they provide a means for minimizing relinking & redeployment of complex systems when localized changes are made.

The name of a stand-alone library, specified with attribute `Library_Name`, must have the syntax of an Ada identifier.

The most prominent characteristic of a stand-alone library is that it offers a distinction between interface units and implementation units. Only the former are visible to units outside the library. A stand-alone library project is thus characterised by a third attribute, usually Library_Interface, in addition to the two attributes that make a project a Library Project (`Library_Name` and `Library_Dir`). This third attribute may also be Interfaces. Library_Interface only works when the interface is in Ada and takes a list of units as parameter. Interfaces works for any supported language and takes a list of sources as parameter.

Library_Interface:
  This attribute defines an explicit subset of the units of the project. Units from projects importing this library project may only "with" units whose sources are listed in the `Library_Interface`. Other sources are considered implementation units.

           for Library_Dir use "lib";
           for Library_Name use "loggin";
           for Library_Interface use ("lib1", "lib2");  --  unit names

Interfaces
  This attribute defines an explicit subset of the source files of a project. Sources from projects importing this project, can only depend on sources from this subset. This attribute can be used on non library projects. It can also be used as a replacement for attribute `Library_Interface`, in which case, units have to be replaced by source files. For multi-language library projects, it is the only way to make the project a Stand-Alone Library project whose interface is not purely Ada.

Library_Standalone:
  This attribute defines the kind of standalone library to build. Values are either `standard` (the default), `no` or `encapsulated`. When `standard` is used the code to elaborate and finalize the library is embedded, when `encapsulated` is used the library can furthermore only depends on static libraries (including the GNAT runtime). This attribute can be set to `no` to make it clear that the library should not be standalone in which case the `Library_Interface` should not defined. Note that this attribute only applies to shared libraries, so `Library_Kind` must be set to `dynamic`.

           for Library_Dir use "lib";
           for Library_Name use "loggin";
           for Library_Kind use "dynamic";
           for Library_Interface use ("lib1", "lib2");  --  unit names
           for Library_Standalone use "encapsulated";

In order to include the elaboration code in the stand-alone library, the binder is invoked on the closure of the library units creating a package whose name depends on the library name (b~logging.ads/b in the example). This binder-generated package includes initialization and finalization procedures whose names depend on the library name (`logginginit` and `loggingfinal` in the example). The object corresponding to this package is included in the library.

Library_Auto_Init:
  A dynamic stand-alone Library is automatically initialized if automatic initialization of Stand-alone Libraries is supported on the platform and if attribute Library_Auto_Init is not specified or is specified with the value "true". A static Stand-alone Library is never automatically initialized. Specifying "false" for this attribute prevent automatic initialization.

  When a non-automatically initialized stand-alone library is used in an executable, its initialization procedure must be called before any service of the library is used. When the main subprogram is in Ada, it may mean that the initialization procedure has to be called during elaboration of another package.

Library_Dir:
  For a stand-alone library, only the ``ALI'` files of the interface units (those that are listed in attribute `Library_Interface`) are copied to the library directory. As a consequence, only the interface units may be imported from Ada units outside of the library. If other units are imported, the binding phase will fail.

Binder.Default_Switches:
  When a stand-alone library is bound, the switches that are specified in the attribute Binder.Default_Switches ("Ada") are used in the call to `gnatbind`.

Library_Src_Dir:
  This attribute defines the location (absolute or relative to the project directory) where the sources of the interface units are copied at installation time. These sources includes the specs of the interface units along with the closure of sources necessary to compile them successfully. That may include bodies and subunits, when pragmas `Inline` are used, or when there is a generic units in the spec. This directory cannot point to the object directory or one of the source directories, but it can point to the library directory, which is the default value for this attribute.

Library_Symbol_Policy:
  This attribute controls the export of symbols and, on some platforms (like VMS) that have the notions of major and minor IDs built in the library files, it controls the setting of these IDs. It is not supported on all platforms (where it will just have no effect). It may have one of the following values:

  - `"autonomous"` or `"default"`: exported symbols are not controlled
  - `"compliant"`: if attribute Library_Reference_Symbol_File is not defined, then it is equivalent to policy "autonomous". If there are exported symbols in the reference symbol file that are not in the object files of the interfaces, the major ID of the library is increased. If there are symbols in the object files of the interfaces that are not in the reference symbol file, these symbols are put at the end of the list in the newly created symbol file and the minor ID is increased.
  - `"controlled"`: the attribute Library_Reference_Symbol_File must be defined. The library will fail to build if the exported symbols in the object files of the interfaces do not match exactly the symbol in the symbol file.
  - `"restricted"`: The attribute Library_Symbol_File must be defined. The library will fail to build if there are symbols in the symbol file that are not in the exported symbols of the object files of the interfaces. Additional symbols in the object files are not added to the symbol file.
  - `"direct"`: The attribute Library_Symbol_File must be defined and must designate an existing file in the object directory. This symbol file is passed directly to the underlying linker without any symbol processing.

Library_Reference_Symbol_File
  This attribute may define the path name of a reference symbol file that is read when the symbol policy is either "compliant" or "controlled", on platforms that support symbol control, such as VMS, when building a stand-alone library. The path may be an absolute path or a path relative to the project directory.

Library_Symbol_File
  This attribute may define the name of the symbol file to be created when building a stand-alone library when the symbol policy is either "compliant", "controlled" or "restricted", on platforms that support symbol control, such as VMS. When symbol policy is "direct", then a file with this name must exist in the object directory.

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### 11.5.4 Installing a library with project files

When using project files, a usable version of the library is created in the directory specified by the `Library_Dir` attribute of the library project file. Thus no further action is needed in order to make use of the libraries that are built as part of the general application build.

You may want to install a library in a context different from where the library is built. This situation arises with third party suppliers, who may want to distribute a library in binary form where the user is not expected to be able to recompile the library. The simplest option in this case is to provide a project file slightly different from the one used to build the library, by using the `externally_built` attribute. 11.5.2 Using Library Projects

Another option is to use `gprinstall` to install the library in a different context than the build location. A project to use this library is generated automatically by `gprinstall` which also copy, in the install location, the minimum set of sources needed to use the library. 11.2.10 Installation

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## 11.6 Project Extension

During development of a large system, it is sometimes necessary to use modified versions of some of the source files, without changing the original sources. This can be achieved through the project extension facility.

Suppose for instance that our example `Build` project is built every night for the whole team, in some shared directory. A developer usually need to work on a small part of the system, and might not want to have a copy of all the sources and all the object files (mostly because that would require too much disk space, time to recompile everything). He prefers to be able to override some of the source files in his directory, while taking advantage of all the object files generated at night.

Another example can be taken from large software systems, where it is common to have multiple implementations of a common interface; in Ada terms, multiple versions of a package body for the same spec. For example, one implementation might be safe for use in tasking programs, while another might only be used in sequential applications. This can be modeled in GNAT using the concept of project extension. If one project (the "child") extends another project (the "parent") then by default all source files of the parent project are inherited by the child, but the child project can override any of the parent's source files with new versions, and can also add new files or remove unnecessary ones. This facility is the project analog of a type extension in object-oriented programming. Project hierarchies are permitted (an extending project may itself be extended), and a project that extends a project can also import other projects.

A third example is that of using project extensions to provide different versions of the same system. For instance, assume that a `Common` project is used by two development branches. One of the branches has now been frozen, and no further change can be done to it or to `Common`. However, the other development branch still needs evolution of `Common`. Project extensions provide a flexible solution to create a new version of a subsystem while sharing and reusing as much as possible from the original one.

A project extension inherits implicitly all the sources and objects from the project it extends. It is possible to create a new version of some of the sources in one of the additional source dirs of the extending project. Those new versions hide the original versions. Adding new sources or removing existing ones is also possible. Here is an example on how to extend the project `Build` from previous examples:

       project Work extends "../bld/build.gpr" is
       end Work;

The project after extends is the one being extended. As usual, it can be specified using an absolute path, or a path relative to any of the directories in the project path (see section 11.3.1 Project Dependencies). This project does not specify source or object directories, so the default value for these attribute will be used that is to say the current directory (where project `Work` is placed). We can already compile that project with

       gnatmake -Pwork

If no sources have been placed in the current directory, this command won't do anything, since this project does not change the sources it inherited from `Build`, therefore all the object files in `Build` and its dependencies are still valid and are reused automatically.

Suppose we now want to supply an alternate version of ``pack.adb'` but use the existing versions of ``pack.ads'` and ``proc.adb'`. We can create the new file Work's current directory (likely by copying the one from the `Build` project and making changes to it. If new packages are needed at the same time, we simply create new files in the source directory of the extending project.

When we recompile, `gnatmake` will now automatically recompile this file (thus creating ``pack.o'` in the current directory) and any file that depends on it (thus creating ``proc.o'`). Finally, the executable is also linked locally.

Note that we could have obtained the desired behavior using project import rather than project inheritance. A `base` project would contain the sources for ``pack.ads'` and ``proc.adb'`, and `Work` would import `base` and add ``pack.adb'`. In this scenario, `base` cannot contain the original version of ``pack.adb'` otherwise there would be 2 versions of the same unit in the closure of the project and this is not allowed. Generally speaking, it is not recommended to put the spec and the body of a unit in different projects since this affects their autonomy and reusability.

In a project file that extends another project, it is possible to indicate that an inherited source is not part of the sources of the extending project. This is necessary sometimes when a package spec has been overridden and no longer requires a body: in this case, it is necessary to indicate that the inherited body is not part of the sources of the project, otherwise there will be a compilation error when compiling the spec.

For that purpose, the attribute Excluded_Source_Files is used. Its value is a list of file names. It is also possible to use attribute `Excluded_Source_List_File`. Its value is the path of a text file containing one file name per line.

    project Work extends "../bld/build.gpr" is
       for Source_Files use ("pack.ads");
       --  New spec of Pkg does not need a completion
       for Excluded_Source_Files use ("pack.adb");
    end Work;

All packages that are not declared in the extending project are inherited from the project being extended, with their attributes, with the exception of `Linker'Linker_Options` which is never inherited. In particular, an extending project retains all the switches specified in the project being extended.

At the project level, if they are not declared in the extending project, some attributes are inherited from the project being extended. They are: `Languages`, `Main` (for a root non library project) and `Library_Name` (for a project extending a library project)

> 11.6.1 Project Hierarchy Extension |  |

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### 11.6.1 Project Hierarchy Extension

One of the fundamental restrictions in project extension is the following: A project is not allowed to import directly or indirectly at the same time an extending project and one of its ancestors.

By means of example, consider the following hierarchy of projects.

       a.gpr  contains package A1
       b.gpr, imports a.gpr and contains B1, which depends on A1
       c.gpr, imports b.gpr and contains C1, which depends on B1

If we want to locally extend the packages `A1` and `C1`, we need to create several extending projects:

       a_ext.gpr which extends a.gpr, and overrides A1
       b_ext.gpr which extends b.gpr and imports a_ext.gpr
       c_ext.gpr which extends c.gpr, imports b_ext.gpr and overrides C1

       project A_Ext extends "a.gpr" is
          for Source_Files use ("a1.adb", "a1.ads");
       end A_Ext;

       with "a_ext.gpr";
       project B_Ext extends "b.gpr" is
       end B_Ext;

       with "b_ext.gpr";
       project C_Ext extends "c.gpr" is
          for Source_Files use ("c1.adb");
       end C_Ext;

The extension ``b_ext.gpr'` is required, even though we are not overriding any of the sources of ``b.gpr'` because otherwise ``c_expr.gpr'` would import ``b.gpr'` which itself knows nothing about ``a_ext.gpr'`.

When extending a large system spanning multiple projects, it is often inconvenient to extend every project in the hierarchy that is impacted by a small change introduced in a low layer. In such cases, it is possible to create an implicit extension of entire hierarchy using extends all relationship.

When the project is extended using `extends all` inheritance, all projects that are imported by it, both directly and indirectly, are considered virtually extended. That is, the project manager creates implicit projects that extend every project in the hierarchy; all these implicit projects do not control sources on their own and use the object directory of the "extending all" project.

It is possible to explicitly extend one or more projects in the hierarchy in order to modify the sources. These extending projects must be imported by the "extending all" project, which will replace the corresponding virtual projects with the explicit ones.

When building such a project hierarchy extension, the project manager will ensure that both modified sources and sources in implicit extending projects that depend on them, are recompiled.

Thus, in our example we could create the following projects instead:

       a_ext.gpr, extends a.gpr and overrides A1
       c_ext.gpr, "extends all" c.gpr, imports a_ext.gpr and overrides C1

       project A_Ext extends "a.gpr" is
          for Source_Files use ("a1.adb", "a1.ads");
       end A_Ext;

       with "a_ext.gpr";
       project C_Ext extends all "c.gpr" is
         for Source_Files use ("c1.adb");
       end C_Ext;

When building project ``c_ext.gpr'`, the entire modified project space is considered for recompilation, including the sources of ``b.gpr'` that are impacted by the changes in `A1` and `C1`.

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## 11.7 Aggregate Projects

Aggregate projects are an extension of the project paradigm, and are meant to solve a few specific use cases that cannot be solved directly using standard projects. This section will go over a few of these use cases to try to explain what you can use aggregate projects for.

> 11.7.1 Building all main programs from a single project tree |  |
> 11.7.2 Building a set of projects with a single command |  |
> 11.7.3 Define a build environment |  |
> 11.7.4 Performance improvements in builder |  |
> 11.7.5 Syntax of aggregate projects |  |
> 11.7.6 package Builder in aggregate projects |  |

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### 11.7.1 Building all main programs from a single project tree

Most often, an application is organized into modules and submodules, which are very conveniently represented as a project tree or graph (the root project A `with`s the projects for each modules (say B and C), which in turn `with` projects for submodules.

Very often, modules will build their own executables (for testing purposes for instance), or libraries (for easier reuse in various contexts).

However, if you build your project through `gnatmake` or `gprbuild`, using a syntax similar to

       gprbuild -PA.gpr

this will only rebuild the main programs of project A, not those of the imported projects B and C. Therefore you have to spawn several `gnatmake` commands, one per project, to build all executables. This is a little inconvenient, but more importantly is inefficient because `gnatmake` needs to do duplicate work to ensure that sources are up-to-date, and cannot easily compile things in parallel when using the -j switch.

Also libraries are always rebuilt when building a project.

You could therefore define an aggregate project Agg that groups A, B and C. Then, when you build with

        gprbuild -PAgg.gpr

this will build all mains from A, B and C.

       aggregate project Agg is
          for Project_Files use ("a.gpr", "b.gpr", "c.gpr");
       end Agg;

If B or C do not define any main program (through their Main attribute), all their sources are built. When you do not group them in the aggregate project, only those sources that are needed by A will be built.

If you add a main to a project P not already explicitly referenced in the aggregate project, you will need to add "p.gpr" in the list of project files for the aggregate project, or the main will not be built when building the aggregate project.

Aggregate projects are only supported with `gprbuild`, but not with `gnatmake`.

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### 11.7.2 Building a set of projects with a single command

One other case is when you have multiple applications and libraries that are built independently from each other (but can be built in parallel). For instance, you have a project tree rooted at A, and another one (which might share some subprojects) rooted at B.

Using only `gprbuild`, you could do

      gprbuild -PA.gpr
      gprbuild -PB.gpr

to build both. But again, `gprbuild` has to do some duplicate work for those files that are shared between the two, and cannot truly build things in parallel efficiently.

If the two projects are really independent, share no sources other than through a common subproject, and have no source files with a common basename, you could create a project C that imports A and B. But these restrictions are often too strong, and one has to build them independently. An aggregate project does not have these limitations and can aggregate two project trees that have common sources.

This scenario is particularly useful in environments like VxWorks 653 where the applications running in the multiple partitions can be built in parallel through a single `gprbuild` command. This also works nicely with Annex E.

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### 11.7.3 Define a build environment

The environment variables at the time you launch `gprbuild` will influence the view these tools have of the project (PATH to find the compiler, ADA_PROJECT_PATH or GPR_PROJECT_PATH to find the projects, environment variables that are referenced in project files through the "external" statement,...). Several command line switches can be used to override those (-X or -aP), but on some systems and with some projects, this might make the command line too long, and on all systems often make it hard to read.

An aggregate project can be used to set the environment for all projects built through that aggregate. One of the nice aspects is that you can put the aggregate project under configuration management, and make sure all your user have a consistent environment when building. The syntax looks like

       aggregate project Agg is
          for Project_Files use ("A.gpr", "B.gpr");
          for Project_Path use ("../dir1", "../dir1/dir2");
          for External ("BUILD") use "PRODUCTION";

          package Builder is
             for Switches ("Ada") use ("-q");
          end Builder;
       end Agg;

One of the often requested features in projects is to be able to reference external variables in `with` statements, as in

      with external("SETUP") & "path/prj.gpr";   --  ILLEGAL
      project MyProject is
         ...
      end MyProject;

For various reasons, this isn't authorized. But using aggregate projects provide an elegant solution. For instance, you could use a project file like:

    aggregate project Agg is
        for Project_Path use (external("SETUP") & "path");
        for Project_Files use ("myproject.gpr");
    end Agg;

    with "prj.gpr";  --  searched on Agg'Project_Path
    project MyProject is
       ...
    end MyProject;

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### 11.7.4 Performance improvements in builder

The loading of aggregate projects is optimized in `gprbuild`, so that all files are searched for only once on the disk (thus reducing the number of system calls and contributing to faster compilation times especially on systems with sources on remote servers). As part of the loading, `gprbuild` computes how and where a source file should be compiled, and even if it is found several times in the aggregated projects it will be compiled only once.

Since there is no ambiguity as to which switches should be used, files can be compiled in parallel (through the usual -j switch) and this can be done while maximizing the use of CPUs (compared to launching multiple `gprbuild` and `gnatmake` commands in parallel).

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### 11.7.5 Syntax of aggregate projects

An aggregate project follows the general syntax of project files. The recommended extension is still ``.gpr'`. However, a special `aggregate` qualifier must be put before the keyword `project`.

An aggregate project cannot `with` any other project (standard or aggregate), except an abstract project which can be used to share attribute values. Also, aggregate projects cannot be extended or imported though a `with` clause by any other project. Building other aggregate projects from an aggregate project is done through the Project_Files attribute (see below).

An aggregate project does not have any source files directly (only through other standard projects). Therefore a number of the standard attributes and packages are forbidden in an aggregate project. Here is the (non exhaustive) list:

- Languages
- Source_Files, Source_List_File and other attributes dealing with list of sources.
- Source_Dirs, Exec_Dir and Object_Dir
- Library_Dir, Library_Name and other library-related attributes
- Main
- Roots
- Externally_Built
- Inherit_Source_Path
- Excluded_Source_Dirs
- Locally_Removed_Files
- Excluded_Source_Files
- Excluded_Source_List_File
- Interfaces

The only package that is authorized (albeit optional) is Builder. Other packages (in particular Compiler, Binder and Linker) are forbidden. It is an error to have any of these (and such an error prevents the proper loading of the aggregate project).

Three new attributes have been created, which can only be used in the context of aggregate projects:

Project_Files:

  This attribute is compulsory (or else we are not aggregating any project, and thus not doing anything). It specifies a list of ``.gpr'` files that are grouped in the aggregate. The list may be empty. The project files can be either other aggregate projects, or standard projects. When grouping standard projects, you can have both the root of a project tree (and you do not need to specify all its imported projects), and any project within the tree.

  Basically, the idea is to specify all those projects that have main programs you want to build and link, or libraries you want to build. You can even specify projects that do not use the Main attribute nor the `Library_*` attributes, and the result will be to build all their source files (not just the ones needed by other projects).

  The file can include paths (absolute or relative). Paths are relative to the location of the aggregate project file itself (if you use a base name, we expect to find the .gpr file in the same directory as the aggregate project file). The environment variables `ADA_PROJECT_PATH`, `GPR_PROJECT_PATH` and `GPR_PROJECT_PATH_FILE` are not used to find the project files. The extension ``.gpr'` is mandatory, since this attribute contains file names, not project names.

  Paths can also include the `"*"` and `"**"` globbing patterns. The latter indicates that any subdirectory (recursively) will be searched for matching files. The latter (`"**"`) can only occur at the last position in the directory part (ie `"a/**/*.gpr"` is supported, but not `"**/a/*.gpr"`). Starting the pattern with `"**"` is equivalent to starting with `"./**"`.

  For now, the pattern `"*"` is only allowed in the filename part, not in the directory part. This is mostly for efficiency reasons to limit the number of system calls that are needed.

  Here are a few valid examples:

          for Project_Files use ("a.gpr", "subdir/b.gpr");
          --  two specific projects relative to the directory of agg.gpr

          for Project_Files use ("**/*.gpr");
          --  all projects recursively

Project_Path:

  This attribute can be used to specify a list of directories in which to look for project files in `with` statements.

  When you specify a project in Project_Files say `"x/y/a.gpr"`), and this projects imports a project "b.gpr", only b.gpr is searched in the project path. a.gpr must be exactly at <dir of the aggregate>/x/y/a.gpr.

  This attribute, however, does not affect the search for the aggregated project files specified with `Project_Files`.

  Each aggregate project has its own (that is if agg1.gpr includes agg2.gpr, they can potentially both have a different project path).

  This project path is defined as the concatenation, in that order, of:

  - the current directory;
  - followed by the command line -aP switches;
  - then the directories from the GPR_PROJECT_PATH and ADA_PROJECT_PATH environment variables;
  - then the directories from the Project_Path attribute;
  - and finally the predefined directories.

  In the example above, agg2.gpr's project path is not influenced by the attribute agg1'Project_Path, nor is agg1 influenced by agg2'Project_Path.

  This can potentially lead to errors. In the following example:

           +---------------+                  +----------------+
           | Agg1.gpr      |-=--includes--=-->| Agg2.gpr       |
           |  'project_path|                  |  'project_path |
           |               |                  |                |
           +---------------+                  +----------------+
                 :                                   :
                 includes                        includes
                 :                                   :
                 v                                   v
             +-------+                          +---------+
             | P.gpr |<---------- withs --------|  Q.gpr  |
             +-------+---------\                +---------+
                 |             |
                 withs         |
                 |             |
                 v             v
             +-------+      +---------+
             | R.gpr |      | R'.gpr  |
             +-------+      +---------+

  When looking for p.gpr, both aggregates find the same physical file on the disk. However, it might happen that with their different project paths, both aggregate projects would in fact find a different r.gpr. Since we have a common project (p.gpr) "with"ing two different r.gpr, this will be reported as an error by the builder.

  Directories are relative to the location of the aggregate project file.

  Here are a few valid examples:

         for Project_Path use ("/usr/local/gpr", "gpr/");

External:

  This attribute can be used to set the value of environment variables as retrieved through the `external` statement in projects. It does not affect the environment variables themselves (so for instance you cannot use it to change the value of your PATH as seen from the spawned compiler).

  This attribute affects the external values as seen in the rest of the aggreate projects, and in the aggregated projects.

  The exact value of external a variable comes from one of three sources (each level overrides the previous levels):

  - An External attribute in aggregate project, for instance `for External ("BUILD_MODE") use "DEBUG"`;

  - Environment variables

    These override the value given by the attribute, so that users can override the value set in the (presumably shared with others in his team) aggregate project.

  - The -X command line switch to `gprbuild`

    This always takes precedence.

  This attribute is only taken into account in the main aggregate project (i.e. the one specified on the command line to `gprbuild`), and ignored in other aggregate projects. It is invalid in standard projects. The goal is to have a consistent value in all projects that are built through the aggregate, which would not be the case in the diamond case: A groups the aggregate projects B and C, which both (either directly or indirectly) build the project P. If B and C could set different values for the environment variables, we would have two different views of P, which in particular might impact the list of source files in P.

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### 11.7.6 package Builder in aggregate projects

As we mentioned before, only the package Builder can be specified in an aggregate project. In this package, only the following attributes are valid:

Switches:
  This attribute gives the list of switches to use for `gprbuild`. Because no mains can be specified for aggregate projects, the only possible index for attribute `Switches` is `others`. All other indexes will be ignored.

  Example:

      for Switches (other) use ("-v", "-k", "-j8");

  These switches are only read from the main aggregate project (the one passed on the command line), and ignored in all other aggregate projects or projects.

  It can only contain builder switches, not compiler switches.

Global_Compilation_Switches

  This attribute gives the list of compiler switches for the various languages. For instance,

      for Global_Compilation_Switches ("Ada") use ("O1", "-g");
      for Global_Compilation_Switches ("C")   use ("-O2");

  This attribute is only taken into account in the aggregate project specified on the command line, not in other aggregate projects.

  In the projects grouped by that aggregate, the attribute Builder.Global_Compilation_Switches is also ignored. However, the attribute Compiler.Default_Switches will be taken into account (but that of the aggregate have higher priority). The attribute Compiler.Switches is also taken into account and can be used to override the switches for a specific file. As a result, it always has priority.

  The rules are meant to avoid ambiguities when compiling. For instance, aggregate project Agg groups the projects A and B, that both depend on C. Here is an extra for all of these projects:

            aggregate project Agg is
                for Project_Files use ("a.gpr", "b.gpr");
                package Builder is
                   for Global_Compilation_Switches ("Ada") use ("-O2");
                end Builder;
            end Agg;

            with "c.gpr";
            project A is
                package Builder is
                   for Global_Compilation_Switches ("Ada") use ("-O1");
                   --  ignored
                end Builder;

                package Compiler is
                   for Default_Switches ("Ada")
                       use ("-O1", "-g");
                   for Switches ("a_file1.adb")
                       use ("-O0");
                end Compiler;
            end A;

            with "c.gpr";
            project B is
                package Compiler is
                   for Default_Switches ("Ada") use ("-O0");
                end Compiler;
            end B;

            project C is
                package Compiler is
                   for Default_Switches ("Ada")
                       use ("-O3",
                            "-gnatn");
                   for Switches ("c_file1.adb")
                       use ("-O0", "-g");
                end Compiler;
            end C;

  then the following switches are used:

  - all files from project A except a_file1.adb are compiled with "-O2 -g", since the aggregate project has priority.
  - the file a_file1.adb is compiled with "-O0", since the Compiler.Switches has priority
  - all files from project B are compiled with "-O2", since the aggregate project has priority
  - all files from C are compiled with "-O2 -gnatn", except for c_file1.adb which is compiled with "-O0 -g"

  Even though C is seen through two paths (through A and through B), the switches used by the compiler are unambiguous.

Global_Configuration_Pragmas

  This attribute can be used to specify a file containing configuration pragmas, to be passed to the Ada compiler. Since we ignore the package Builder in other aggregate projects and projects, only those pragmas defined in the main aggregate project will be taken into account.

  Projects can locally add to those by using the `Compiler.Local_Configuration_Pragmas` attribute if they need.

Global_Config_File

  This attribute, indexed with a language name, can be used to specify a config when compiling sources of the language. For Ada, these files are configuration pragmas files.

For projects that are built through the aggregate, the package Builder is ignored, except for the Executable attribute which specifies the name of the executables resulting from the link of the main programs, and for the Executable_Suffix.

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## 11.8 Aggregate Library Projects

Aggregate library projects make it possible to build a single library using object files built using other standard or library projects. This gives the flexibility to describe an application as having multiple modules (a GUI, database access, ...) using different project files (so possibly built with different compiler options) and yet create a single library (static or relocatable) out of the corresponding object files.

> 11.8.1 Building aggregate library projects |  |
> 11.8.2 Syntax of aggregate library projects |  |

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### 11.8.1 Building aggregate library projects

For example, we can define an aggregate project Agg that groups A, B and C:

       aggregate library project Agg is
          for Project_Files use ("a.gpr", "b.gpr", "c.gpr");
          for Library_Name use ("agg");
          for Library_Dir use ("lagg");
       end Agg;

Then, when you build with:

        gprbuild agg.gpr

This will build all units from projects A, B and C and will create a static library named ``libagg.a'` into the ``lagg'` directory. An aggregate library project has the same set of restriction as a standard library project.

Note that a shared aggregate library project cannot aggregates a static library project. In platforms where a compiler option is required to create relocatable object files, a Builder package in the aggregate library project may be used:

       aggregate library project Agg is
          for Project_Files use ("a.gpr", "b.gpr", "c.gpr");
          for Library_Name use ("agg");
          for Library_Dir use ("lagg");
          for Library_Kind use "relocatable";

          package Builder is
             for Global_Compilation_Switches ("Ada") use ("-fPIC");
          end Builder;
       end Agg;

With the above aggregate library Builder package, the `-fPIC` option will be passed to the compiler when building any source code from projects ``a.gpr'`, ``b.gpr'` and ``c.gpr'`.

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### 11.8.2 Syntax of aggregate library projects

An aggregate library project follows the general syntax of project files. The recommended extension is still ``.gpr'`. However, a special `aggregate library` qualifier must be put before the keyword `project`.

An aggregate library project cannot `with` any other project (standard or aggregate), except an abstract project which can be used to share attribute values.

An aggregate library project does not have any source files directly (only through other standard projects). Therefore a number of the standard attributes and packages are forbidden in an aggregate library project. Here is the (non exhaustive) list:

- Languages
- Source_Files, Source_List_File and other attributes dealing with list of sources.
- Source_Dirs, Exec_Dir and Object_Dir
- Main
- Roots
- Externally_Built
- Inherit_Source_Path
- Excluded_Source_Dirs
- Locally_Removed_Files
- Excluded_Source_Files
- Excluded_Source_List_File
- Interfaces

The only package that is authorized (albeit optional) is Builder.

The Project_Files attribute (See see section 11.7 Aggregate Projects) is used to described the aggregated projects whose object files have to be included into the aggregate library. The environment variables `ADA_PROJECT_PATH`, `GPR_PROJECT_PATH` and `GPR_PROJECT_PATH_FILE` are not used to find the project files.

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## 11.9 Project File Reference

This section describes the syntactic structure of project files, the various constructs that can be used. Finally, it ends with a summary of all available attributes.

> 11.9.1 Project Declaration |  |
> 11.9.2 Qualified Projects |  |
> 11.9.3 Declarations |  |
> 11.9.4 Packages |  |
> 11.9.5 Expressions |  |
> 11.9.6 External Values |  |
> 11.9.7 Typed String Declaration |  |
> 11.9.8 Variables |  |
> 11.9.9 Case Constructions |  |
> 11.9.10 Attributes |  |

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### 11.9.1 Project Declaration

Project files have an Ada-like syntax. The minimal project file is:

    project Empty is
    end Empty;

The identifier `Empty` is the name of the project. This project name must be present after the reserved word `end` at the end of the project file, followed by a semi-colon.

Identifiers (i.e. the user-defined names such as project or variable names) have the same syntax as Ada identifiers: they must start with a letter, and be followed by zero or more letters, digits or underscore characters; it is also illegal to have two underscores next to each other. Identifiers are always case-insensitive ("Name" is the same as "name").

    simple_name ::= identifier
    name        ::= simple_name { . simple_name }

Strings are used for values of attributes or as indexes for these attributes. They are in general case sensitive, except when noted otherwise (in particular, strings representing file names will be case insensitive on some systems, so that "file.adb" and "File.adb" both represent the same file).

Reserved words are the same as for standard Ada 95, and cannot be used for identifiers. In particular, the following words are currently used in project files, but others could be added later on. In bold are the extra reserved words in project files: `all, at, case, end, for, is, limited, null, others, package, renames, type, use, when, with, extends, external, project`.

Comments in project files have the same syntax as in Ada, two consecutive hyphens through the end of the line.

A project may be an independent project, entirely defined by a single project file. Any source file in an independent project depends only on the predefined library and other source files in the same project. But a project may also depend on other projects, either by importing them through with clauses, or by extending at most one other project. Both types of dependency can be used in the same project.

A path name denotes a project file. It can be absolute or relative. An absolute path name includes a sequence of directories, in the syntax of the host operating system, that identifies uniquely the project file in the file system. A relative path name identifies the project file, relative to the directory that contains the current project, or relative to a directory listed in the environment variables ADA_PROJECT_PATH and GPR_PROJECT_PATH. Path names are case sensitive if file names in the host operating system are case sensitive. As a special case, the directory separator can always be "/" even on Windows systems, so that project files can be made portable across architectures. The syntax of the environment variable ADA_PROJECT_PATH and GPR_PROJECT_PATH is a list of directory names separated by colons on UNIX and semicolons on Windows.

A given project name can appear only once in a context clause.

It is illegal for a project imported by a context clause to refer, directly or indirectly, to the project in which this context clause appears (the dependency graph cannot contain cycles), except when one of the with clause in the cycle is a limited with.

    with "other_project.gpr";
    project My_Project extends "extended.gpr" is
    end My_Project;

These dependencies form a directed graph, potentially cyclic when using limited with. The subprogram reflecting the extends relations is a tree.

A project's immediate sources are the source files directly defined by that project, either implicitly by residing in the project source directories, or explicitly through any of the source-related attributes. More generally, a project sources are the immediate sources of the project together with the immediate sources (unless overridden) of any project on which it depends directly or indirectly.

A project hierarchy can be created, where projects are children of other projects. The name of such a child project must be `Parent.Child`, where `Parent` is the name of the parent project. In particular, this makes all `with` clauses of the parent project automatically visible in the child project.

    project        ::= context_clause project_declaration

    context_clause ::= {with_clause}
    with_clause    ::= with path_name { , path_name } ;
    path_name      ::= string_literal

    project_declaration ::= simple_project_declaration | project_extension
    simple_project_declaration ::=
      project <project_>name is
        {declarative_item}
      end <project_>simple_name;

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### 11.9.2 Qualified Projects

Before the reserved `project`, there may be one or two qualifiers, that is identifiers or reserved words, to qualify the project. The current list of qualifiers is:

abstract: qualifies a project with no sources. Such a
  project must either have no declaration of attributes `Source_Dirs`, `Source_Files`, `Languages` or `Source_List_File`, or one of `Source_Dirs`, `Source_Files`, or `Languages` must be declared as empty. If it extends another project, the project it extends must also be a qualified abstract project.
standard: a standard project is a non library project with sources.
  This is the default (implicit) qualifier.
aggregate: a project whose sources are aggregated from other
  project files.
aggregate library: a library whose sources are aggregated
  from other project or library project files.
library: a library project must declare both attributes
  `Library_Name` and `Library_Dir`.
configuration: a configuration project cannot be in a project tree.
  It describes compilers and other tools to `gprbuild`.

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### 11.9.3 Declarations

Declarations introduce new entities that denote types, variables, attributes, and packages. Some declarations can only appear immediately within a project declaration. Others can appear within a project or within a package.

    declarative_item ::= simple_declarative_item
      | typed_string_declaration
      | package_declaration

    simple_declarative_item ::= variable_declaration
      | typed_variable_declaration
      | attribute_declaration
      | case_construction
      | empty_declaration

    empty_declaration ::= null ;

An empty declaration is allowed anywhere a declaration is allowed. It has no effect.

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### 11.9.4 Packages

A project file may contain packages, that group attributes (typically all the attributes that are used by one of the GNAT tools).

A package with a given name may only appear once in a project file. The following packages are currently supported in project files (See see section 11.9.10 Attributes for the list of attributes that each can contain).

`Binder`
  This package specifies characteristics useful when invoking the binder either directly via the `gnat` driver or when using a builder such as `gnatmake` or `gprbuild`. See section 11.2.4 Main Subprograms.
`Builder`
  This package specifies the compilation options used when building an executable or a library for a project. Most of the options should be set in one of `Compiler`, `Binder` or `Linker` packages, but there are some general options that should be defined in this package. See section 11.2.4 Main Subprograms, and see section 11.2.7 Executable File Names in particular.
`Check`
  This package specifies the options used when calling the checking tool `gnatcheck` via the `gnat` driver. Its attribute Default_Switches has the same semantics as for the package `Builder`. The first string should always be `-rules` to specify that all the other options belong to the `-rules` section of the parameters to `gnatcheck`.
`Clean`
  This package specifies the options used when cleaning a project or a project tree using the tools `gnatclean` or `gprclean`.
`Compiler`
  This package specifies the compilation options used by the compiler for each languages. See section 11.2.5 Tools Options in Project Files.
`Cross_Reference`
  This package specifies the options used when calling the library tool `gnatxref` via the `gnat` driver. Its attributes Default_Switches and Switches have the same semantics as for the package `Builder`.
`Eliminate`
  This package specifies the options used when calling the tool `gnatelim` via the `gnat` driver. Its attributes Default_Switches and Switches have the same semantics as for the package `Builder`.
`Finder`
  This package specifies the options used when calling the search tool `gnatfind` via the `gnat` driver. Its attributes Default_Switches and Switches have the same semantics as for the package `Builder`.
`Gnatls`
  This package specifies the options to use when invoking `gnatls` via the `gnat` driver.
`Gnatstub`
  This package specifies the options used when calling the tool `gnatstub` via the `gnat` driver. Its attributes Default_Switches and Switches have the same semantics as for the package `Builder`.
`IDE`
  This package specifies the options used when starting an integrated development environment, for instance `GPS` or `Gnatbench`.
`Install`
  This package specifies the options used when installing a project with `gprinstall`. See section 11.2.10 Installation.
`Linker`
  This package specifies the options used by the linker. See section 11.2.4 Main Subprograms.
`Metrics`
  This package specifies the options used when calling the tool `gnatmetric` via the `gnat` driver. Its attributes Default_Switches and Switches have the same semantics as for the package `Builder`.
`Naming`
  This package specifies the naming conventions that apply to the source files in a project. In particular, these conventions are used to automatically find all source files in the source directories, or given a file name to find out its language for proper processing. See section 11.2.9 Naming Schemes.
`Pretty_Printer`
  This package specifies the options used when calling the formatting tool `gnatpp` via the `gnat` driver. Its attributes Default_Switches and Switches have the same semantics as for the package `Builder`.
`Remote`
  This package is used by `gprbuild` to describe how distributed compilation should be done.
`Stack`
  This package specifies the options used when calling the tool `gnatstack` via the `gnat` driver. Its attributes Default_Switches and Switches have the same semantics as for the package `Builder`.
`Synchronize`
  This package specifies the options used when calling the tool `gnatsync` via the `gnat` driver.

In its simplest form, a package may be empty:

    project Simple is
      package Builder is
      end Builder;
    end Simple;

A package may contain attribute declarations, variable declarations and case constructions, as will be described below.

When there is ambiguity between a project name and a package name, the name always designates the project. To avoid possible confusion, it is always a good idea to avoid naming a project with one of the names allowed for packages or any name that starts with `gnat`.

A package can also be defined by a renaming declaration. The new package renames a package declared in a different project file, and has the same attributes as the package it renames. The name of the renamed package must be the same as the name of the renaming package. The project must contain a package declaration with this name, and the project must appear in the context clause of the current project, or be its parent project. It is not possible to add or override attributes to the renaming project. If you need to do so, you should use an extending declaration (see below).

Packages that are renamed in other project files often come from project files that have no sources: they are just used as templates. Any modification in the template will be reflected automatically in all the project files that rename a package from the template. This is a very common way to share settings between projects.

Finally, a package can also be defined by an extending declaration. This is similar to a renaming declaration, except that it is possible to add or override attributes.

    package_declaration ::= package_spec | package_renaming | package_extension
    package_spec ::=
      package <package_>simple_name is
        {simple_declarative_item}
      end package_identifier ;
    package_renaming ::==
      package <package_>simple_name renames <project_>simple_name.package_identifier ;
    package_extension ::==
      package <package_>simple_name extends <project_>simple_name.package_identifier is
        {simple_declarative_item}
      end package_identifier ;

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### 11.9.5 Expressions

An expression is any value that can be assigned to an attribute or a variable. It is either a literal value, or a construct requiring runtime computation by the project manager. In a project file, the computed value of an expression is either a string or a list of strings.

A string value is one of:

- A literal string, for instance `"comm/my_proj.gpr"`
- The name of a variable that evaluates to a string (see section 11.9.8 Variables)
- The name of an attribute that evaluates to a string (see section 11.9.10 Attributes)
- An external reference (see section 11.9.6 External Values)
- A concatenation of the above, as in `"prefix_" & Var`.

A list of strings is one of the following:

- A parenthesized comma-separated list of zero or more string expressions, for instance `(File_Name, "gnat.adc", File_Name & ".orig")` or `()`.
- The name of a variable that evaluates to a list of strings
- The name of an attribute that evaluates to a list of strings
- A concatenation of a list of strings and a string (as defined above), for instance `("A", "B") & "C"`
- A concatenation of two lists of strings

The following is the grammar for expressions

    string_literal ::= "{string_element}"  --  Same as Ada
    string_expression ::= string_literal
        | variable_name
        | external_value
        | attribute_reference
        | ( string_expression { & string_expression } )
    string_list  ::= ( string_expression { , string_expression } )
       | string_variable_name
       | string_attribute_reference
    term ::= string_expression | string_list
    expression ::= term { & term }     --  Concatenation

Concatenation involves strings and list of strings. As soon as a list of strings is involved, the result of the concatenation is a list of strings. The following Ada declarations show the existing operators:

      function "&" (X : String;      Y : String)      return String;
      function "&" (X : String_List; Y : String)      return String_List;
      function "&" (X : String_List; Y : String_List) return String_List;

Here are some specific examples:

       List := () & File_Name; --  One string in this list
       List2 := List & (File_Name & ".orig"); -- Two strings
       Big_List := List & Lists2;  --  Three strings
       Illegal := "gnat.adc" & List2;  --  Illegal, must start with list

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### 11.9.6 External Values

An external value is an expression whose value is obtained from the command that invoked the processing of the current project file (typically a `gnatmake` or `gprbuild` command).

There are two kinds of external values, one that returns a single string, and one that returns a string list.

The syntax of a single string external value is:

    external_value ::= external ( string_literal [, string_literal] )

The first string_literal is the string to be used on the command line or in the environment to specify the external value. The second string_literal, if present, is the default to use if there is no specification for this external value either on the command line or in the environment.

Typically, the external value will either exist in the environment variables or be specified on the command line through the ``-Xvbl=value'` switch. If both are specified, then the command line value is used, so that a user can more easily override the value.

The function `external` always returns a string. It is an error if the value was not found in the environment and no default was specified in the call to `external`.

An external reference may be part of a string expression or of a string list expression, and can therefore appear in a variable declaration or an attribute declaration.

Most of the time, this construct is used to initialize typed variables, which are then used in case statements to control the value assigned to attributes in various scenarios. Thus such variables are often called scenario variables.

The syntax for a string list external value is:

    external_value ::= external_as_list ( string_literal , string_literal )

The first string_literal is the string to be used on the command line or in the environment to specify the external value. The second string_literal is the separator between each component of the string list.

If the external value does not exist in the environment or on the command line, the result is an empty list. This is also the case, if the separator is an empty string or if the external value is only one separator.

Any separator at the beginning or at the end of the external value is discarded. Then, if there is no separator in the external value, the result is a string list with only one string. Otherwise, any string between the beginning and the first separator, between two consecutive separators and between the last separator and the end are components of the string list.

       external_as_list ("SWITCHES", ",")

If the external value is "-O2,-g", the result is ("-O2", "-g").

If the external value is ",-O2,-g,", the result is also ("-O2", "-g").

if the external value is "-gnatv", the result is ("-gnatv").

If the external value is ",,", the result is ("").

If the external value is ",", the result is (), the empty string list.

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### 11.9.7 Typed String Declaration

A type declaration introduces a discrete set of string literals. If a string variable is declared to have this type, its value is restricted to the given set of literals. These are the only named types in project files. A string type may only be declared at the project level, not inside a package.

    typed_string_declaration ::=
      type <typed_string_>_simple_name is ( string_literal {, string_literal} );

The string literals in the list are case sensitive and must all be different. They may include any graphic characters allowed in Ada, including spaces. Here is an example of a string type declaration:

       type OS is ("NT", "nt", "Unix", "GNU/Linux", "other OS");

Variables of a string type are called typed variables; all other variables are called untyped variables. Typed variables are particularly useful in `case` constructions, to support conditional attribute declarations. (see section 11.9.9 Case Constructions).

A string type may be referenced by its name if it has been declared in the same project file, or by an expanded name whose prefix is the name of the project in which it is declared.

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### 11.9.8 Variables

Variables store values (strings or list of strings) and can appear as part of an expression. The declaration of a variable creates the variable and assigns the value of the expression to it. The name of the variable is available immediately after the assignment symbol, if you need to reuse its old value to compute the new value. Before the completion of its first declaration, the value of a variable defaults to the empty string ("").

A typed variable can be used as part of a case expression to compute the value, but it can only be declared once in the project file, so that all case constructions see the same value for the variable. This provides more consistency and makes the project easier to understand. The syntax for its declaration is identical to the Ada syntax for an object declaration. In effect, a typed variable acts as a constant.

An untyped variable can be declared and overridden multiple times within the same project. It is declared implicitly through an Ada assignment. The first declaration establishes the kind of the variable (string or list of strings) and successive declarations must respect the initial kind. Assignments are executed in the order in which they appear, so the new value replaces the old one and any subsequent reference to the variable uses the new value.

A variable may be declared at the project file level, or within a package.

    typed_variable_declaration ::=
      <typed_variable_>simple_name : <typed_string_>name := string_expression;
    variable_declaration ::= <variable_>simple_name := expression;

Here are some examples of variable declarations:

       This_OS : OS := external ("OS"); --  a typed variable declaration
       That_OS := "GNU/Linux";          --  an untyped variable declaration

       Name      := "readme.txt";
       Save_Name := Name & ".saved";

       Empty_List := ();
       List_With_One_Element := ("-gnaty");
       List_With_Two_Elements := List_With_One_Element & "-gnatg";
       Long_List := ("main.ada", "pack1_.ada", "pack1.ada", "pack2_.ada");

A variable reference may take several forms:

- The simple variable name, for a variable in the current package (if any) or in the current project
- An expanded name, whose prefix is a context name.

A context may be one of the following:

- The name of an existing package in the current project
- The name of an imported project of the current project
- The name of an ancestor project (i.e., a project extended by the current project, either directly or indirectly)
- An expanded name whose prefix is an imported/parent project name, and whose selector is a package name in that project.

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### 11.9.9 Case Constructions

A case statement is used in a project file to effect conditional behavior. Through this statement, you can set the value of attributes and variables depending on the value previously assigned to a typed variable.

All choices in a choice list must be distinct. Unlike Ada, the choice lists of all alternatives do not need to include all values of the type. An `others` choice must appear last in the list of alternatives.

The syntax of a `case` construction is based on the Ada case statement (although the `null` statement for empty alternatives is optional).

The case expression must be a typed string variable, whose value is often given by an external reference (see section 11.9.6 External Values).

Each alternative starts with the reserved word `when`, either a list of literal strings separated by the `"|"` character or the reserved word `others`, and the `"=>"` token. Each literal string must belong to the string type that is the type of the case variable. After each `=>`, there are zero or more statements. The only statements allowed in a case construction are other case constructions, attribute declarations and variable declarations. String type declarations and package declarations are not allowed. Variable declarations are restricted to variables that have already been declared before the case construction.

    case_statement ::=
      case <typed_variable_>name is {case_item} end case ;

    case_item ::=
      when discrete_choice_list =>
        {case_statement
          | attribute_declaration
          | variable_declaration
          | empty_declaration}

    discrete_choice_list ::= string_literal {| string_literal} | others

Here is a typical example:

    project MyProj is
       type OS_Type is ("GNU/Linux", "Unix", "NT", "VMS");
       OS : OS_Type := external ("OS", "GNU/Linux");

       package Compiler is
         case OS is
           when "GNU/Linux" | "Unix" =>
             for Switches ("Ada")
                 use ("-gnath");
           when "NT" =>
             for Switches ("Ada")
                 use ("-gnatP");
           when others =>
             null;
         end case;
       end Compiler;
    end MyProj;

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### 11.9.10 Attributes

> 11.9.10.1 Project Level Attributes |  |
> 11.9.10.2 Package Binder Attributes |  |
> 11.9.10.3 Package Builder Attributes |  |
> 11.9.10.4 Package Check Attributes |  |
> 11.9.10.5 Package Clean Attributes |  |
> 11.9.10.6 Package Compiler Attributes |  |
> 11.9.10.7 Package Cross_Reference Attributes |  |
> 11.9.10.8 Package Eliminate Attributes |  |
> 11.9.10.9 Package Finder Attributes |  |
> 11.9.10.10 Package gnatls Attributes |  |
> 11.9.10.11 Package gnatstub Attributes |  |
> 11.9.10.12 Package IDE Attributes |  |
> 11.9.10.13 Package Install Attributes |  |
> 11.9.10.14 Package Linker Attributes |  |
> 11.9.10.15 Package Metrics Attribute |  |
> 11.9.10.16 Package Naming Attributes |  |
> 11.9.10.17 Package Pretty_Printer Attributes |  |
> 11.9.10.18 Package Remote Attributes |  |
> 11.9.10.19 Package Stack Attributes |  |
> 11.9.10.20 Package Synchronize Attributes |  |

A project (and its packages) may have attributes that define the project's properties. Some attributes have values that are strings; others have values that are string lists.

    attribute_declaration ::=
       simple_attribute_declaration | indexed_attribute_declaration
    simple_attribute_declaration ::= for attribute_designator use expression ;
    indexed_attribute_declaration ::=
      for <indexed_attribute_>simple_name ( string_literal) use expression ;
    attribute_designator ::=
      <simple_attribute_>simple_name
      | <indexed_attribute_>simple_name ( string_literal )

There are two categories of attributes: simple attributes and indexed attributes. Each simple attribute has a default value: the empty string (for string attributes) and the empty list (for string list attributes). An attribute declaration defines a new value for an attribute, and overrides the previous value. The syntax of a simple attribute declaration is similar to that of an attribute definition clause in Ada.

Some attributes are indexed. These attributes are mappings whose domain is a set of strings. They are declared one association at a time, by specifying a point in the domain and the corresponding image of the attribute. Like untyped variables and simple attributes, indexed attributes may be declared several times. Each declaration supplies a new value for the attribute, and replaces the previous setting.

Here are some examples of attribute declarations:

       --  simple attributes
       for Object_Dir use "objects";
       for Source_Dirs use ("units", "test/drivers");

       --  indexed attributes
       for Body ("main") use "Main.ada";
       for Switches ("main.ada")
           use ("-v", "-gnatv");
       for Switches ("main.ada") use Builder'Switches ("main.ada") & "-g";

       --  indexed attributes copy (from package Builder in project Default)
       --  The package name must always be specified, even if it is the current
       --  package.
       for Default_Switches use Default.Builder'Default_Switches;

Attributes references may appear anywhere in expressions, and are used to retrieve the value previously assigned to the attribute. If an attribute has not been set in a given package or project, its value defaults to the empty string or the empty list.

    attribute_reference ::= attribute_prefix ' <simple_attribute>_simple_name [ (string_literal) ]
    attribute_prefix ::= project
      | <project_>simple_name
      | package_identifier
      | <project_>simple_name . package_identifier

Examples are:

      project'Object_Dir
      Naming'Dot_Replacement
      Imported_Project'Source_Dirs
      Imported_Project.Naming'Casing
      Builder'Default_Switches ("Ada")

The prefix of an attribute may be:

- `project` for an attribute of the current project
- The name of an existing package of the current project
- The name of an imported project
- The name of a parent project that is extended by the current project
- An expanded name whose prefix is imported/parent project name, and whose selector is a package name

In the following sections, all predefined attributes are succinctly described, first the project level attributes, that is those attributes that are not in a package, then the attributes in the different packages.

It is possible for different tools to create dynamically new packages with attributes, or new attribute in predefined packages. These attributes are not documented here.

The attributes under Configuration headings are usually found only in configuration project files.

The characteristics of each attribute are indicated as follows:

- Type of value

  The value of an attribute may be a single string, indicated by the word "single", or a string list, indicated by the word "list".

- Read-only

  When the attribute is read-only, that is when it is not allowed to declare the attribute, this is indicated by the words "read-only".

- Optional index

  If it is allowed in the value of the attribute (both single and list) to have an optional index, this is indicated by the words "optional index".

- Indexed attribute

  When an it is an indexed attribute, this is indicated by the word "indexed".

- Case-sensitivity of the index

  For an indexed attribute, if the index is case-insensitive, this is indicated by the words "case-insensitive index".

- File name index

  For an indexed attribute, when the index is a file name, this is indicated by the words "file name index". The index may or may not be case-sensitive, depending on the platform.

- others allowed in index

  For an indexed attribute, if it is allowed to use others as the index, this is indicated by the words "others allowed".

  When others is used as the index of an indexed attribute, the value of the attribute indexed by others is used when no other index would apply.

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#### 11.9.10.1 Project Level Attributes

- General

  - Name: single, read-only

    The name of the project.

  - Project_Dir: single, read-only

    The path name of the project directory.

  - Main: list, optional index

    The list of main sources for the executables.

  - Languages: list

    The list of languages of the sources of the project.

  - Roots: list, indexed, file name index

    The index is the file name of an executable source. Indicates the list of units from the main project that need to be bound and linked with their closures with the executable. The index is either a file name, a language name or "*". The roots for an executable source are those in Roots with an index that is the executable source file name, if declared. Otherwise, they are those in Roots with an index that is the language name of the executable source, if present. Otherwise, they are those in Roots ("*"), if declared. If none of these three possibilities are declared, then there are no roots for the executable source.

  - Externally_Built: single

    Indicates if the project is externally built. Only case-insensitive values allowed are "true" and "false", the default.

- Directories

  - Object_Dir: single

    Indicates the object directory for the project.

  - Exec_Dir: single

    Indicates the exec directory for the project, that is the directory where the executables are.

  - Source_Dirs: list

    The list of source directories of the project.

  - Inherit_Source_Path: list, indexed, case-insensitive index

    Index is a language name. Value is a list of language names. Indicates that in the source search path of the index language the source directories of the languages in the list should be included.

    Example:

    for Inherit_Source_Path ("C++") use ("C");

  - Exclude_Source_Dirs: list

    The list of directories that are included in Source_Dirs but are not source directories of the project.

  - Ignore_Source_Sub_Dirs: list

    Value is a list of simple names for subdirectories that are removed from the list of source directories, including theur subdirectories.

- Source Files

  - Source_Files: list

    Value is a list of source file simple names.

  - Locally_Removed_Files: list

    Obsolescent. Equivalent to Excluded_Source_Files.

  - Excluded_Source_Files: list

    Value is a list of simple file names that are not sources of the project. Allows to remove sources that are inherited or found in the source directories and that match the naming scheme.

  - Source_List_File: single

    Value is a text file name that contains a list of source file simple names, one on each line.

  - Excluded_Source_List_File: single

    Value is a text file name that contains a list of file simple names that are not sources of the project.

  - Interfaces: list

    Value is a list of file names that constitutes the interfaces of the project.

- Aggregate Projects

  - Project_Files: list

    Value is the list of aggregated projects.

  - Project_Path: list

    Value is a list of directories that are added to the project search path when looking for the aggregated projects.

  - External: single, indexed

    Index is the name of an external reference. Value is the value of the external reference to be used when parsing the aggregated projects.

- Libraries

  - Library_Dir: single

    Value is the name of the library directory. This attribute needs to be declared for each library project.

  - Library_Name: single

    Value is the name of the library. This attribute needs to be declared or inherited for each library project.

  - Library_Kind: single

    Specifies the kind of library: static library (archive) or shared library. Case-insensitive values must be one of "static" for archives (the default) or "dynamic" or "relocatable" for shared libraries.

  - Library_Version: single

    Value is the name of the library file.

  - Library_Interface: list

    Value is the list of unit names that constitutes the interfaces of a Stand-Alone Library project.

  - Library_Standalone: single

    Specifies if a Stand-Alone Library (SAL) is encapsulated or not. Only authorized case-insensitive values are "standard" for non encapsulated SALs, "encapsulated" for encapsulated SALs or "no" for non SAL library project.

  - Library_Encapsulated_Options: list

    Value is a list of options that need to be used when linking an encapsulated Stand-Alone Library.

  - Library_Encapsulated_Supported: single

    Indicates if encapsulated Stand-Alone Libraries are supported. Only authorized case-insensitive values are "true" and "false" (the default).

  - Library_Auto_Init: single

    Indicates if a Stand-Alone Library is auto-initialized. Only authorized case-insentive values are "true" and "false".

  - Leading_Library_Options: list

    Value is a list of options that are to be used at the beginning of the command line when linking a shared library.

  - Library_Options: list

    Value is a list of options that are to be used when linking a shared library.

  - Library_Rpath_Options: list, indexed, case-insensitive index

    Index is a language name. Value is a list of options for an invocation of the compiler of the language. This invocation is done for a shared library project with sources of the language. The output of the invocation is the path name of a shared library file. The directory name is to be put in the run path option switch when linking the shared library for the project.

  - Library_Src_Dir: single

    Value is the name of the directory where copies of the sources of the interfaces of a Stand-Alone Library are to be copied.

  - Library_ALI_Dir: single

    Value is the name of the directory where the ALI files of the interfaces of a Stand-Alone Library are to be copied. When this attribute is not declared, the directory is the library directory.

  - Library_gcc: single

    Obsolescent attribute. Specify the linker driver used to link a shared library. Use instead attribute Linker'Driver.

  - Library_Symbol_File: single

    Value is the name of the library symbol file.

  - Library_Symbol_Policy: single

    Indicates the symbol policy kind. Only authorized case-insensitive values are "autonomous", "default", "compliant", "controlled" or "direct".

  - Library_Reference_Symbol_File: single

    Value is the name of the reference symbol file.

- Configuration - General

  - Default_Language: single

    Value is the case-insensitive name of the language of a project when attribute Languages is not specified.

  - Run_Path_Option: list

    Value is the list of switches to be used when specifying the run path option in an executable.

  - Run_Path_Origin: single

    Value is the the string that may replace the path name of the executable directory in the run path options.

  - Separate_Run_Path_Options: single

    Indicates if there may be or not several run path options specified when linking an executable. Only authorized case-insensitive b=values are "true" or "false" (the default).

  - Toolchain_Version: single, indexed, case-insensitive index

    Index is a language name. Specify the version of a toolchain for a language.

  - Toolchain_Description: single, indexed, case-insensitive index

    Obsolescent. No longer used.

  - Object_Generated: single, indexed, case-insensitive index

    Index is a language name. Indicates if invoking the compiler for a language produces an object file. Only authorized case-insensitive values are "false" and "true" (the default).

  - Objects_Linked: single, indexed, case-insensitive index

    Index is a language name. Indicates if the object files created by the compiler for a language need to be linked in the executable. Only authorized case-insensitive values are "false" and "true" (the default).

  - Target: single

    Value is the name of the target platform.

- Configuration - Libraries

  - Library_Builder: single

    Value is the path name of the application that is to be used to build libraries. Usually the path name of "gprlib".

  - Library_Support: single

    Indicates the level of support of libraries. Only authorized case-insensitive values are "static_only", "full" or "none" (the default).

- Configuration - Archives

  - Archive_Builder: list

    Value is the name of the application to be used to create a static library (archive), followed by the options to be used.

  - Archive_Builder_Append_Option: list

    Value is the list of options to be used when invoking the archive builder to add project files into an archive.

  - Archive_Indexer: list

    Value is the name of the archive indexer, followed by the required options.

  - Archive_Suffix: single

    Value is the extension of archives. When not declared, the extension is ".a".

  - Library_Partial_Linker: list

    Value is the name of the partial linker executable, followed by the required options.

- Configuration - Shared Libraries

  - Shared_Library_Prefix: single

    Value is the prefix in the name of shared library files. When not declared, the prefix is "lib".

  - Shared_Library_Suffix: single

    Value is the the extension of the name of shared library files. When not declared, the extension is ".so".

  - Symbolic_Link_Supported: single

    Indicates if symbolic links are supported on the platform. Only authorized case-insensitive values are "true" and "false" (the default).

  - Library_Major_Minor_Id_Supported: single

    Indicates if major and minor ids for shared library names are supported on the platform. Only authorized case-insensitive values are "true" and "false" (the default).

  - Library_Auto_Init_Supported: single

    Indicates if auto-initialization of Stand-Alone Libraries is supported. Only authorized case-insensitive values are "true" and "false" (the default).

  - Shared_Library_Minimum_Switches: list

    Value is the list of required switches when linking a shared library.

  - Library_Version_Switches: list

    Value is the list of switches to specify a internal name for a shared library.

  - Library_Install_Name_Option: single

    Value is the name of the option that needs to be used, concatenated with the path name of the library file, when linking a shared library.

  - Runtime_Library_Dir: single, indexed, case-insensitive index

    Index is a language name. Value is the path name of the directory where the runtime libraries are located.

  - Runtime_Source_Dir: single, indexed, case-insensitive index

    Index is a language name. Value is the path name of the directory where the sources of runtime libraries are located.

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#### 11.9.10.2 Package Binder Attributes

- General

  - Default_Switches: list, indexed, case-insensitive index

    Index is a language name. Value is the list of switches to be used when binding code of the language, if there is no applicable attribute Switches.

  - Switches: list, optional index, indexed, case-insensitive index, others allowed

    Index is either a language name or a source file name. Value is the list of switches to be used when binding code. Index is either the source file name of the executable to be bound or the language name of the code to be bound.

- Configuration - Binding

  - Driver: single, indexed, case-insensitive index

    Index is a language name. Value is the name of the application to be used when binding code of the language.

  - Required_Switches: list, indexed, case-insensitive index

    Index is a language name. Value is the list of the required switches to be used when binding code of the language.

  - Prefix: single, indexed, case-insensitive index

    Index is a language name. Value is a prefix to be used for the binder exchange file name for the language. Used to have different binder exchange file names when binding different languages.

  - Objects_Path: single,indexed, case-insensitive index

    Index is a language name. Value is the name of the environment variable that contains the path for the object directories.

  - Object_Path_File: single,indexed, case-insensitive index

    Index is a language name. Value is the name of the environment variable. The value of the environment variable is the path name of a text file that contains the list of object directories.

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#### 11.9.10.3 Package Builder Attributes

- Default_Switches: list, indexed, case-insensitive index

  Index is a language name. Value is the list of builder switches to be used when building an executable of the language, if there is no applicable attribute Switches.

- Switches: list, optional index, indexed, case-insensitive index, others allowed

  Index is either a language name or a source file name. Value is the list of builder switches to be used when building an executable. Index is either the source file name of the executable to be built or its language name.

- Global_Compilation_Switches: list, optional index, indexed, case-insensitive index

  Index is either a language name or a source file name. Value is the list of compilation switches to be used when building an executable. Index is either the source file name of the executable to be built or its language name.

- Executable: single, indexed, case-insensitive index

  Index is an executable source file name. Value is the simple file name of the executable to be built.

- Executable_Suffix: single

  Value is the extension of the file names of executable. When not specified, the extension is the default extension of executables on the platform.

- Global_Configuration_Pragmas: single

  Value is the file name of a configuration pragmas file that is specified to the Ada compiler when compiling any Ada source in the project tree.

- Global_Config_File: single, indexed, case-insensitive index

  Index is a language name. Value is the file name of a configuration file that is specified to the compiler when compiling any source of the language in the project tree.

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#### 11.9.10.4 Package Check Attributes

- Default_Switches: list, indexed, case-insensitive index

  Index is a language name. Value is a list of switches to be used when invoking `gnatcheck` for a source of the language, if there is no applicable attribute Switches.

- Switches: list, optional index, indexed, case-insensitive index, others allowed

  Index is a source file name. Value is the list of switches to be used when invoking `gnatcheck` for the source.

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#### 11.9.10.5 Package Clean Attributes

- Switches: list

  Value is a list of switches to be used by the cleaning application.

- Source_Artifact_Extensions: list, indexed, case-insensitive index

  Index is a language names. Value is the list of extensions for file names derived from object file names that need to be cleaned in the object directory of the project.

- Object_Artifact_Extensions: list, indexed, case-insensitive index

  Index is a language names. Value is the list of extensions for file names derived from source file names that need to be cleaned in the object directory of the project.

- Artifacts_In_Object_Dir: single

  Value is a list of file names expressed as regular expressions that are to be deleted by gprclean in the object directory of the project.

- Artifacts_In_Exec_Dir: single

  Value is list of file names expressed as regular expressions that are to be deleted by gprclean in the exec directory of the main project.

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#### 11.9.10.6 Package Compiler Attributes

- General

  - Default_Switches: list, indexed, case-insensitive index

    Index is a language name. Value is a list of switches to be used when invoking the compiler for the language for a source of the project, if there is no applicable attribute Switches.

  - Switches: list, optional index, indexed, case-insensitive index, others allowed

    Index is a source file name or a language name. Value is the list of switches to be used when invoking the compiler for the source or for its language.

  - Local_Configuration_Pragmas: single

    Value is the file name of a configuration pragmas file that is specified to the Ada compiler when compiling any Ada source in the project.

  - Local_Config_File: single, indexed, case-insensitive index

    Index is a language name. Value is the file name of a configuration file that is specified to the compiler when compiling any source of the language in the project.

- Configuration - Compiling

  - Driver: single, indexed, case-insensitive index

    Index is a language name. Value is the name of the executable for the compiler of the language.

  - Language_Kind: single, indexed, case-insensitive index

    Index is a language name. Indicates the kind of the language, either file based or unit based. Only authorized case-insensitive values are "unit_based" and "file_based" (the default).

  - Dependency_Kind: single, indexed, case-insensitive index

    Index is a language name. Indicates how the dependencies are handled for the language. Only authorized case-insensitive values are "makefile", "ali_file", "ali_closure" or "none" (the default).

  - Required_Switches: list, indexed, case-insensitive index

    Equivalent to attribute Leading_Required_Switches.

  - Leading_Required_Switches: list, indexed, case-insensitive index

    Index is a language name. Value is the list of the minimum switches to be used at the beginning of the command line when invoking the compiler for the language.

  - Trailing_Required_Switches: list, indexed, case-insensitive index

    Index is a language name. Value is the list of the minimum switches to be used at the end of the command line when invoking the compiler for the language.

  - PIC_Option: list, indexed, case-insensitive index

    Index is a language name. Value is the list of switches to be used when compiling a source of the language when the project is a shared library project.

  - Path_Syntax: single, indexed, case-insensitive index

    Index is a language name. Value is the kind of path syntax to be used when invoking the compiler for the language. Only authorized case-insensitive values are "canonical" and "host" (the default).

  - Source_File_Switches: single, indexed, case-insensitive index

    Index is a language name. Value is a list of switches to be used just before the path name of the source to compile when invoking the compiler for a source of the language.

  - Object_File_Suffix: single, indexed, case-insensitive index

    Index is a language name. Value is the extension of the object files created by the compiler of the language. When not specified, the extension is the default one for the platform.

  - Object_File_Switches: list, indexed, case-insensitive index

    Index is a language name. Value is the list of switches to be used by the compiler of the language to specify the path name of the object file. When not specified, the switch used is "-o".

  - Multi_Unit_Switches: list, indexed, case-insensitive index

    Index is a language name. Value is the list of switches to be used to compile a unit in a multi unit source of the language. The index of the unit in the source is concatenated with the last switches in the list.

  - Multi_Unit_Object_Separator: single, indexed, case-insensitive index

    Index is a language name. Value is the string to be used in the object file name before the index of the unit, when compiling a unit in a multi unit source of the language.

- Configuration - Mapping Files

  - Mapping_File_Switches: list, indexed, case-insensitive index

    Index is a language name. Value is the list of switches to be used to specify a mapping file when invoking the compiler for a source of the language.

  - Mapping_Spec_Suffix: single, indexed, case-insensitive index

    Index is a language name. Value is the suffix to be used in a mapping file to indicate that the source is a spec.

  - Mapping_Body_Suffix: single, indexed, case-insensitive index

    Index is a language name. Value is the suffix to be used in a mapping file to indicate that the source is a body.

- Configuration - Config Files

  - Config_File_Switches: list: single, indexed, case-insensitive index

    Index is a language name. Value is the list of switches to specify to the compiler of the language a configuration file.

  - Config_Body_File_Name: single, indexed, case-insensitive index

    Index is a language name. Value is the template to be used to indicate a configuration specific to a body of the language in a configuration file.

  - Config_Body_File_Name_Index: single, indexed, case-insensitive index

    Index is a language name. Value is the template to be used to indicate a configuration specific to the body a unit in a multi unit source of the language in a configuration file.

  - Config_Body_File_Name_Pattern: single, indexed, case-insensitive index

    Index is a language name. Value is the template to be used to indicate a configuration for all bodies of the languages in a configuration file.

  - Config_Spec_File_Name: single, indexed, case-insensitive index

    Index is a language name. Value is the template to be used to indicate a configuration specific to a spec of the language in a configuration file.

  - Config_Spec_File_Name_Index: single, indexed, case-insensitive index

    Index is a language name. Value is the template to be used to indicate a configuration specific to the spec a unit in a multi unit source of the language in a configuration file.

  - Config_Spec_File_Name_Pattern: single, indexed, case-insensitive index

    Index is a language name. Value is the template to be used to indicate a configuration for all specs of the languages in a configuration file.

  - Config_File_Unique: single, indexed, case-insensitive index

    Index is a language name. Indicates if there should be only one configuration file specified to the compiler of the language. Only authorized case-insensitive values are "true" and "false" (the default).

- Configuration - Dependencies

  - Dependency_Switches: list, indexed, case-insensitive index

    Index is a language name. Value is the list of switches to be used to specify to the compiler the dependency file when the dependency kind of the language is file based, and when Dependency_Driver is not specified for the language.

  - Dependency_Driver: list, indexed, case-insensitive index

    Index is a language name. Value is the name of the executable to be used to create the dependency file for a source of the language, followed by the required switches.

- Configuration - Search Paths

  - Include_Switches: list, indexed, case-insensitive index

    Index is a language name. Value is the list of switches to specify to the compiler of the language to indicate a directory to look for sources.

  - Include_Path: single, indexed, case-insensitive index

    Index is a language name. Value is the name of an environment variable that contains the path of all the directories that the compiler of the language may search for sources.

  - Include_Path_File: single, indexed, case-insensitive index

    Index is a language name. Value is the name of an environment variable the value of which is the path name of a text file that contains the directories that the compiler of the language may search for sources.

  - Object_Path_Switches: list, indexed, case-insensitive index

    Index is a language name. Value is the list of switches to specify to the compiler of the language the name of a text file that contains the list of object directories. When this attribute is not declared, the text file is not created.

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#### 11.9.10.7 Package Cross_Reference Attributes

- Default_Switches: list, indexed, case-insensitive index

  Index is a language name. Value is a list of switches to be used when invoking `gnatxref` for a source of the language, if there is no applicable attribute Switches.

- Switches: list, optional index, indexed, case-insensitive index, others allowed

  Index is a source file name. Value is the list of switches to be used when invoking `gnatxref` for the source.

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#### 11.9.10.8 Package Eliminate Attributes

- Default_Switches: list, indexed, case-insensitive index

  Index is a language name. Value is a list of switches to be used when invoking `gnatelim` for a source of the language, if there is no applicable attribute Switches.

- Switches: list, optional index, indexed, case-insensitive index, others allowed

  Index is a source file name. Value is the list of switches to be used when invoking `gnatelim` for the source.

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#### 11.9.10.9 Package Finder Attributes

- Default_Switches: list, indexed, case-insensitive index

  Index is a language name. Value is a list of switches to be used when invoking `gnatfind` for a source of the language, if there is no applicable attribute Switches.

- Switches: list, optional index, indexed, case-insensitive index, others allowed

  Index is a source file name. Value is the list of switches to be used when invoking `gnatfind` for the source.

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#### 11.9.10.10 Package gnatls Attributes

- Switches: list

  Value is a list of switches to be used when invoking `gnatls`.

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#### 11.9.10.11 Package gnatstub Attributes

- Default_Switches: list, indexed, case-insensitive index

  Index is a language name. Value is a list of switches to be used when invoking `gnatstub` for a source of the language, if there is no applicable attribute Switches.

- Switches: list, optional index, indexed, case-insensitive index, others allowed

  Index is a source file name. Value is the list of switches to be used when invoking `gnatstub` for the source.

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#### 11.9.10.12 Package IDE Attributes

- Default_Switches: list, indexed

  Index is the name of an external tool that the GNAT Programming System (GPS) is supporting. Value is a list of switches to use when invoking that tool.

- Remote_Host: single

  Value is a string that designates the remote host in a cross-compilation environment, to be used for remote compilation and debugging. This attribute should not be specified when running on the local machine.

- Program_Host: single

  Value is a string that specifies the name of IP address of the embedded target in a cross-compilation environment, on which the program should execute.

- Communication_Protocol: single

  Value is the name of the protocol to use to communicate with the target in a cross-compilation environment, for example `"wtx"` or `"vxworks"`.

- Compiler_Command: single, indexed, case-insensitive index

  Index is a language Name. Value is a string that denotes the command to be used to invoke the compiler. The value of `Compiler_Command ("Ada")` is expected to be compatible with `gnatmake`, in particular in the handling of switches.

- Debugger_Command: single

  Value is a string that specifies the name of the debugger to be used, such as gdb, powerpc-wrs-vxworks-gdb or gdb-4.

- gnatlist: single

  Value is a string that specifies the name of the `gnatls` utility to be used to retrieve information about the predefined path; for example, `"gnatls"`, `"powerpc-wrs-vxworks-gnatls"`.

- VCS_Kind: single

  Value is a string used to specify the Version Control System (VCS) to be used for this project, for example "Subversion", "ClearCase". If the value is set to "Auto", the IDE will try to detect the actual VCS used on the list of supported ones.

- VCS_File_Check: single

  Value is a string that specifies the command used by the VCS to check the validity of a file, either when the user explicitly asks for a check, or as a sanity check before doing the check-in.

- VCS_Log_Check: single

  Value is a string that specifies the command used by the VCS to check the validity of a log file.

- Documentation_Dir: single

  Value is the directory used to generate the documentation of source code.

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#### 11.9.10.13 Package Install Attributes

- Prefix: single

  Value is the install destination directory.

- Sources_Subdir: single

  Value is the sources directory or subdirectory of Prefix.

- Exec_Subdir: single

  Value is the executables directory or subdirectory of Prefix.

- Lib_Subdir: single

  Value is library directory or subdirectory of Prefix.

- Project_Subdir: single

  Value is the project directory or subdirectory of Prefix.

- Active: single

  Indicates that the project is to be installed or not. Case-insensitive value "false" means that the project is not to be installed, all other values mean that the project is to be installed.

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#### 11.9.10.14 Package Linker Attributes

- General

  - Required_Switches: list

    Value is a list of switches that are required when invoking the linker to link an executable.

  - Default_Switches: list, indexed, case-insensitive index

    Index is a language name. Value is a list of switches for the linker when linking an executable for a main source of the language, when there is no applicable Switches.

  - Leading_Switches: list, optional index, indexed, case-insensitive index, others allowed

    Index is a source file name or a language name. Value is the list of switches to be used at the beginning of the command line when invoking the linker to build an executable for the source or for its language.

  - Switches: list, optional index, indexed, case-insensitive index, others allowed

    Index is a source file name or a language name. Value is the list of switches to be used when invoking the linker to build an executable for the source or for its language.

  - Trailing_Switches: list, optional index, indexed, case-insensitive index, others allowed

    Index is a source file name or a language name. Value is the list of switches to be used at the end of the command line when invoking the linker to build an executable for the source or for its language. These switches may override the Required_Switches.

  - Linker_Options: list

    Value is a list of switches/options that are to be added when linking an executable from a project importing the current project directly or indirectly. Linker_Options are not used when linking an executable from the current project.

  - Map_File_Option: single

    Value is the switch to specify the map file name that the linker needs to create.

- Configuration - Linking

  - Driver: single

    Value is the name of the linker executable.

- Configuration - Response Files

  - Max_Command_Line_Length: single

    Value is the maximum number of character in the command line when invoking the linker to link an executable.

  - Response_File_Format: single

    Indicates the kind of response file to create when the length of the linking command line is too large. Only authorized case-insensitive values are "none", "gnu", "object_list", "gcc_gnu", "gcc_option_list" and "gcc_object_list".

  - Response_File_Switches: list

    Value is the list of switches to specify a response file to the linker.

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#### 11.9.10.15 Package Metrics Attribute

- Default_Switches: list, indexed, case-insensitive index

  Index is a language name. Value is a list of switches to be used when invoking `gnatmetric` for a source of the language, if there is no applicable attribute Switches.

- Switches: list, optional index, indexed, case-insensitive index, others allowed

  Index is a source file name. Value is the list of switches to be used when invoking `gnatmetric` for the source.

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#### 11.9.10.16 Package Naming Attributes

- Specification_Suffix: single, indexed, case-insensitive index

  Equivalent to attribute Spec_Suffix.

- Spec_Suffix: single, indexed, case-insensitive index

  Index is a language name. Value is the extension of file names for specs of the language.

- Implementation_Suffix: single, indexed, case-insensitive index

  Equivalent to attribute Body_Suffix.

- Body_Suffix: single, indexed, case-insensitive index

  Index is a language name. Value is the extension of file names for bodies of the language.

- Separate_Suffix: single

  Value is the extension of file names for subunits of Ada.

- Casing: single

  Indicates the casing of sources of the Ada language. Only authorized case-insensitive values are "lowercase", "uppercase" and "mixedcase".

- Dot_Replacement: single

  Value is the string that replace the dot of unit names in the source file names of the Ada language.

- Specification: single, optional index, indexed, case-insensitive index

  Equivalent to attribute Spec.

- Spec: single, optional index, indexed, case-insensitive index

  Index is a unit name. Value is the file name of the spec of the unit.

- Implementation: single, optional index, indexed, case-insensitive index

  Equivalent to attribute Body.

- Body: single, optional index, indexed, case-insensitive index

  Index is a unit name. Value is the file name of the body of the unit.

- Specification_Exceptions: list, indexed, case-insensitive index

  Index is a language name. Value is a list of specs for the language that do not necessarily follow the naming scheme for the language and that may or may not be found in the source directories of the project.

- Implementation_Exceptions: list, indexed, case-insensitive index

  Index is a language name. Value is a list of bodies for the language that do not necessarily follow the naming scheme for the language and that may or may not be found in the source directories of the project.

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#### 11.9.10.17 Package Pretty_Printer Attributes

- Default_Switches: list, indexed, case-insensitive index

  Index is a language name. Value is a list of switches to be used when invoking `gnatpp` for a source of the language, if there is no applicable attribute Switches.

- Switches: list, optional index, indexed, case-insensitive index, others allowed

  Index is a source file name. Value is the list of switches to be used when invoking `gnatpp` for the source.

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#### 11.9.10.18 Package Remote Attributes

- Included_Patterns: list

  If this attribute is defined it sets the patterns to synchronized from the master to the slaves. It is exclusive with Excluded_Patterns, that is it is an error to define both.

- Included_Artifact_Patterns: list

  If this attribute is defined it sets the patterns of compilation artifacts to synchronized from the slaves to the build master. This attribute replace the default hard-coded patterns.

- Excluded_Patterns: list

  Set of patterns to ignore when synchronizing sources from the build master to the slaves. A set of predefined patterns are supported (e.g. *.o, *.ali, *.exe, etc.), this attributes make it possible to add some more patterns.

- Root_Dir: single

  Value is the root directory used by the slave machines.

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#### 11.9.10.19 Package Stack Attributes

- Switches: list

  Value is the list of switches to be used when invoking `gnatstack`.

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#### 11.9.10.20 Package Synchronize Attributes

- Default_Switches: list, indexed, case-insensitive index

  Index is a language name. Value is a list of switches to be used when invoking `gnatsync` for a source of the language, if there is no applicable attribute Switches.

- Switches: list, optional index, indexed, case-insensitive index, others allowed

  Index is a source file name. Value is the list of switches to be used when invoking `gnatsync` for the source.

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