A new SCons release, 4.9.0, is now available on the SCons download page:

    https://scons.org/pages/download.html

Here is a summary of the changes since 4.8.1:

NOTE: Since SCons 4.9.0, Python 3.7.0 or above is required.


CHANGED/ENHANCED EXISTING FUNCTIONALITY
---------------------------------------
- Expose the `extra_libs` keyword argument in `CheckLibWithHeader` and 'CheckLib'

- Removed Python 3.6 support.

- Override environments, created when giving construction environment
  keyword arguments to Builder calls (or manually, through the
  undocumented Override method), were modified not to "leak" on item deletion.
  The item will now not be deleted from the base environment.

- Added support for tracking beamer themes in the LaTeX scanner.

- MSVS: msvs project files are always generated before the corresponding
  msvs solution files. This changes the behavior of clean for a project
  generated with auto_build_solution disabled and explicit solution
  generation: when the solution files are cleaned, the project files are
  also cleaned.  The tests for vs 6.0-7.1 were updated accordingly.

- MSVS: Add an optional keyword argument, auto_filter_projects, to
  MSVSSolution. Accepted values for auto_filter_projects are:

  - None [default]: raise an exception when solution file names or nodes
    are detected in the projects argument list.
  - True or evaluates True: automatically remove solution file names and
    nodes from the project argument list.
  - False or evaluates False: leave solution file names and nodes in the
    project argument list.  An exception is not raised.

  Solution file names and/or nodes in the project argument list cause
  erroneous Project records to be produced in the generated solution file.
  As a convenience, a user may elect to ignore solution file names and nodes
  in the projects argument list rather than manually removing solution file
  names and nodes from the MSVSProject return values.

- SCons C preprocessor:

  - Update the optional integer suffixes to include the z|Z and wb|WB
    suffixes.
  - Add support for binary integer constants.
  - Add support for octal integer constants.  Previously, octal integers
    were evaluated as decimal integers.  A literal zero (0) is treated as an
    octal number.
  - Change the method for attempted conversion of a define expansion value
    to an integer from a literal to a constant expression evaluation.

- Add a tag to each CacheDir to let systems ignore backing it up
  (per https://bford.info/cachedir/). Update the way a CacheDir
  is created, since it now has to create two files.

- The Dictionary method now has an as_dict flag. If true, Dictionary
  always returns  a dict. The default remains to return different
  types depending on whether zero, one, or multiple construction

- A Variables object now makes available a "defaulted" attribute,
  a list of variable names that were set in the environment with
  their values taken from the default in the variable description
  (if a variable was set to the same value as the default in one
  of the input sources, it is not included in this list).

- If a build Variable is created with no aliases, the name of the
  Variable is no longer listed in its aliases. Internally, the name
  and aliases are considered together anyway so this should not have
  any effect except for being visible to custom help text formatters.

FIXES
-----

- PackageVariable now does what the documentation always said it does
  if the variable is used on the command line with one of the enabling
  string as the value: the variable's default value is produced (previously
  it always produced True in this case).

- Temporary files created by TempFileMunge() are now cleaned up on
  scons exit, instead of at the time they're used.  Fixes #4595.

- AddOption now correctly adds short (single-character) options.
  Previously an added short option would always report as unknown,
  while long option names for the same option worked. Short options
  that take a value require the user to specify the value immediately
  following the option, with no spaces (e.g. -j5 and not -j 5).

- Fix a problem with compilation_db component initialization - the
  entries for assembler files were not being set up correctly.

- On Darwin, PermissionErrors are now handled while trying to access
  /etc/paths.d. This may occur if SCons is invoked in a sandboxed environment
  (such as Nix).

- Added error handling when creating MSVC detection debug log file specified
  by SCONS_MSCOMMON_DEBUG.

- MSVS: Modify select msvs test scripts to run on platforms not supported by
  the msvs/msvc tool implementation via a default host architecture for
  unsupported platforms.

- MSVS: Fixed early loop exit in select msvs test scripts.  Select msvs test
  scripts were being invoked for msvc version 8.0 only.  Additional msvs
  tool and test changes due to the msvs test scripts being run for all msvc
  versions (i.e., minor test and tool issues went undetected).

- MSVS: for variant build configurations, msvs solution files are
  generated in the source directory and a placeholder file is generated in
  the variant build directory.  This mirrors the behavior of generated
  msvs project files.

- MSVS: msvs project files are generated before the corresponding msvs
  solution file.  User-specified project GUIDs should now be correctly
  written to the solution file.

- SCons C preprocessor: Preserve literals that contain valid integer
  substring specifications.  Previously, the integer suffix could be
  stripped from a symbol that contained an integer and suffix substring.

- SCons C preprocessor: Update the optional integer suffixes to include
  support for the alternate orderings of unsigned with long or long long as
  defined in the c/cpp grammar.

- SCons C preprocessor: Update the optional integer suffixes for case
  insensitive specifications as defined in the c/cpp grammar.

- Fix nasm test for missing include file, cleanup.

- Skip running a few validation tests if the user is root and the test is
  not designed to work for the root user.

- Make sure unknown variables from a Variables file are recognized
  as such. Previously only unknowns from the command line were
  recognized (issue #4645).

- Update ninja tool to use ninja.BIN_DIR to find pypi packaged ninja binary.
  python ninja package version 1.11.1.2 changed the location and previous
  logic no longer worked.

- The (optional) C Conditional Scanner now does limited macro
  replacement on the contents of CPPDEFINES, to improve finding deps
  that are conditionally included.  Previously replacement was only
  done on macro definitions found in the file being scanned.
  Only object-like macros are replaced (not function-like), and
  only on a whole-word basis; recursion is limited to five levels
  and does not error out if that limit is reached (issue #4523).

- Minor modernization: make use of stat object's st_mode, st_mtime
  and other attributes rather than indexing into stat return.

- Ninja's TEMPLATE rule pool changed from `local_pool` to `install_pool`
  hoping it will fix a race condition that can occurs when Ninja defers
  to SCons to build.

- Renamed env.Help() & Help()'s argument `keep_local` to `local_only`, previously the documentation
  specified `local_only`, but the code and tests were using `keep_local`. The functionality
  more closely matches local only.  NOTE: It doesn't seem like any code in the wild was using
  local_only as we'd not received any reports of such until PR #4606 from hedger.

- Fix Issue #2281, AddPreAction() & AddPostAction() were being ignored if no action
  was specified when the Alias was initially created.

- Handle case of "memoizer" as one member of a comma-separated
  --debug string - this was previously missed.

IMPROVEMENTS
------------

- For consistency with the optparse "add_option" method, AddOption accepts
  an SConsOption object as a single argument (this failed previously).
  Calling AddOption with the full set of arguments (option names and
  attributes) to set up the option is still the recommended approach.

- Add clang and clang++ to the default tool search orders for POSIX
  and Windows platforms. These will be searched for after gcc and g++,
  respectively. Does not affect explicitly requested tool lists.  Note:
  on Windows, SCons currently only has builtin support for clang, not
  for clang-cl, the version of the frontend that uses cl.exe-compatible
  command line switches.


DOCUMENTATION
-------------

- Some manpage cleanup for the gettext and pdf/ps builders.

- Some clarifications in the User Guide "Environments" chapter.

- Clarify documentation of Repository() in manpage and user guide.

- Many grammatical and spelling fixes in the documentation.

- Update Clean and NoClean documentation.

- Improved Variables documentation.

- Update the User Guide Command() example which now shows a target name
  being created from '${SOURCE.base}.out' to use a valid special
  attribute and to explain what's being done in the example.

DEVELOPMENT
-----------

- Ruff/Mypy: Excluded items now synced.

- Ruff: Linter includes new rules - `FA`, `UP006`, `UP007`, and `UP037` - to
  detect and upgrade legacy type-hint syntax.

- Removed "SCons.Util.sctyping.py", as the functionality can now be substituted
  via top-level `from __future__ import annotations`.

- Implemented type hints for Nodes.

- Added TestSCons.NINJA_BINARY to TestSCons to centralize logic to find ninja binary

- Refactored SCons.Tool.ninja -> SCons.Tool.ninja_tool, and added alias so env.Tool('ninja')
  will still work. This avoids conflicting with the pypi module ninja.

Thanks to the following contributors listed below for their contributions to this release.
==========================================================================================
.. code-block:: text

    git shortlog --no-merges -ns 4.8.1..HEAD
    50  Mats Wichmann
    46  William Deegan
    19  Joseph Brill
    10  Alex Thiessen
     4  Thaddeus Crews
     3  Ruben Di Battista
     2  Adam Scott
     2  Keith F. Prussing
     2  Prabhu Singh Khalsa
     1  Adam Simpkins
     1  Alex James
     1  Yevhen Babiichuk (DustDFG)

