.. _ext-intersphinx:

:mod:`sphinx.ext.intersphinx` -- Link to other projects' documentation
======================================================================

.. module:: sphinx.ext.intersphinx
   :synopsis: Link to other Sphinx documentation.

.. index:: pair: automatic; linking

.. versionadded:: 0.5

This extension can generate links to the documentation of objects in external
projects, either explicitly through the :rst:role:`external` role, or as a
fallback resolution for any other cross-reference.

Usage for fallback resolution is simple: whenever Sphinx encounters a
cross-reference that has no matching target in the current documentation set,
it looks for targets in the external documentation sets configured in
:confval:`intersphinx_mapping`.  A reference like
``:py:class:`zipfile.ZipFile``` can then link to the Python documentation
for the ZipFile class, without you having to specify where it is located
exactly.

When using the :rst:role:`external` role, you can force lookup to any external
projects, and optionally to a specific external project.
A link like ``:external:ref:`comparison manual <comparisons>``` will then link
to the label "comparisons" in whichever configured external project, if it
exists,
and a link like ``:external+python:ref:`comparison manual <comparisons>``` will
link to the label "comparisons" only in the doc set "python", if it exists.

Behind the scenes, this works as follows:

* Each Sphinx HTML build creates a file named :file:`objects.inv` that contains
  a mapping from object names to URIs relative to the HTML set's root.

* Projects using the Intersphinx extension can specify the location of such
  mapping files in the :confval:`intersphinx_mapping` config value.  The mapping
  will then be used to resolve both :rst:role:`external` references, and also
  otherwise missing references to objects into links to the other documentation.

* By default, the mapping file is assumed to be at the same location as the rest
  of the documentation; however, the location of the mapping file can also be
  specified individually, e.g. if the docs should be buildable without Internet
  access.


Configuration
-------------

To use Intersphinx linking, add ``'sphinx.ext.intersphinx'`` to your
:confval:`extensions` config value, and use these config values to activate
linking:

.. confval:: intersphinx_mapping

   This config value contains the locations and names of other projects that
   should be linked to in this documentation.

   Relative local paths for target locations are taken as relative to the base
   of the built documentation, while relative local paths for inventory
   locations are taken as relative to the source directory.

   When fetching remote inventory files, proxy settings will be read from
   the ``$HTTP_PROXY`` environment variable.

   **Format**

   .. versionadded:: 1.0

   A dictionary mapping unique identifiers to a tuple ``(target, inventory)``.
   Each ``target`` is the base URI of a foreign Sphinx documentation set and can
   be a local path or an HTTP URI.  The ``inventory`` indicates where the
   inventory file can be found: it can be ``None`` (an :file:`objects.inv` file
   at the same location as the base URI) or another local file path or a full
   HTTP URI to an inventory file.

   The unique identifier can be used in the :rst:role:`external` role, so that
   it is clear which intersphinx set the target belongs to.  A link like
   ``:external+python:ref:`comparison manual <comparisons>``` will link to the
   label "comparisons" in the doc set "python", if it exists.

   **Example**

   To add links to modules and objects in the Python standard library
   documentation, use::

      intersphinx_mapping = {'python': ('https://docs.python.org/3', None)}

   This will download the corresponding :file:`objects.inv` file from the
   Internet and generate links to the pages under the given URI.  The downloaded
   inventory is cached in the Sphinx environment, so it must be re-downloaded
   whenever you do a full rebuild.

   A second example, showing the meaning of a non-``None`` value of the second
   tuple item::

      intersphinx_mapping = {'python': ('https://docs.python.org/3',
                                        'python-inv.txt')}

   This will read the inventory from :file:`python-inv.txt` in the source
   directory, but still generate links to the pages under
   ``https://docs.python.org/3``.  It is up to you to update the inventory file
   as new objects are added to the Python documentation.

   **Multiple targets for the inventory**

   .. versionadded:: 1.3

   Alternative files can be specified for each inventory. One can give a
   tuple for the second inventory tuple item as shown in the following
   example. This will read the inventory iterating through the (second)
   tuple items until the first successful fetch. The primary use case for
   this to specify mirror sites for server downtime of the primary
   inventory::

      intersphinx_mapping = {'python': ('https://docs.python.org/3',
                                        (None, 'python-inv.txt'))}

   For a set of books edited and tested locally and then published
   together, it could be helpful to try a local inventory file first,
   to check references before publication::

      intersphinx_mapping = {
          'otherbook':
              ('https://myproj.readthedocs.io/projects/otherbook/en/latest',
                  ('../../otherbook/build/html/objects.inv', None)),
      }

.. confval:: intersphinx_cache_limit

   The maximum number of days to cache remote inventories.  The default is
   ``5``, meaning five days.  Set this to a negative value to cache inventories
   for unlimited time.

.. confval:: intersphinx_timeout

   The number of seconds for timeout.  The default is ``None``, meaning do not
   timeout.

   .. note::

      timeout is not a time limit on the entire response download; rather, an
      exception is raised if the server has not issued a response for timeout
      seconds.

.. confval:: intersphinx_disabled_reftypes

   .. versionadded:: 4.3

   .. versionchanged:: 5.0

      Changed default value from an empty list to ``['std:doc']``.

   A list of strings being either:

   - the name of a specific reference type in a domain,
     e.g., ``std:doc``, ``py:func``, or ``cpp:class``,
   - the name of a domain, and a wildcard, e.g.,
     ``std:*``, ``py:*``, or ``cpp:*``, or
   - simply a wildcard ``*``.

   The default value is ``['std:doc']``.

   When a non-:rst:role:`external` cross-reference is being resolved by
   intersphinx, skip resolution if it matches one of the specifications in this
   list.

   For example, with ``intersphinx_disabled_reftypes = ['std:doc']``
   a cross-reference ``:doc:`installation``` will not be attempted to be
   resolved by intersphinx, but ``:external+otherbook:doc:`installation``` will
   be attempted to be resolved in the inventory named ``otherbook`` in
   :confval:`intersphinx_mapping`.
   At the same time, all cross-references generated in, e.g., Python,
   declarations will still be attempted to be resolved by intersphinx.

   If ``*`` is in the list of domains, then no non-:rst:role:`external`
   references will be resolved by intersphinx.

Explicitly Reference External Objects
-------------------------------------

The Intersphinx extension provides the following role.

.. rst:role:: external

   .. versionadded:: 4.4

   Use Intersphinx to perform lookup only in external projects, and not the
   current project. Intersphinx still needs to know the type of object you
   would like to find, so the general form of this role is to write the
   cross-refererence as if the object is in the current project, but then prefix
   it with ``:external``.
   The two forms are then

   - ``:external:domain:reftype:`target```,
     e.g., ``:external:py:class:`zipfile.ZipFile```, or
   - ``:external:reftype:`target```,
     e.g., ``:external:doc:`installation```.
     With this shorthand, the domain is assumed to be ``std``.

   If you would like to constrain the lookup to a specific external project,
   then the key of the project, as specified in :confval:`intersphinx_mapping`,
   is added as well to get the two forms

   - ``:external+invname:domain:reftype:`target```,
     e.g., ``:external+python:py:class:`zipfile.ZipFile```, or
   - ``:external+invname:reftype:`target```,
     e.g., ``:external+python:doc:`installation```.

Showing all links of an Intersphinx mapping file
------------------------------------------------

To show all Intersphinx links and their targets of an Intersphinx mapping file,
run ``python -msphinx.ext.intersphinx url-or-path``.  This is helpful when
searching for the root cause of a broken Intersphinx link in a documentation
project. The following example prints the Intersphinx mapping of the Python 3
documentation::

   $ python -m sphinx.ext.intersphinx https://docs.python.org/3/objects.inv

Using Intersphinx with inventory file under Basic Authorization
---------------------------------------------------------------

Intersphinx supports Basic Authorization like this::

      intersphinx_mapping = {'python': ('https://user:password@docs.python.org/3',
                                        None)}

The user and password will be stripped from the URL when generating the links.
