Allow extensions to define the keys returned by linkcode (#11824)

Co-authored-by: Adam Turner <9087854+aa-turner@users.noreply.github.com>

CHANGES.rst

@@ -21,6 +21,9 @@ Features added
 * Add a new ``duplicate_declaration`` warning type,
   with ``duplicate_declaration.c`` and ``duplicate_declaration.cpp`` subtypes.
   Patch by Julien Lecomte and Adam Turner.
+* #11824: linkcode: Allow extensions to add support for a domain by defining
+  the keys that should be present.
+  Patch by Nicolas Peugnet.
 
 Bugs fixed
 ----------

doc/usage/extensions/linkcode.rst

@@ -49,3 +49,21 @@ Configuration
               return None
           filename = info['module'].replace('.', '/')
           return "https://somesite/sourcerepo/%s.py" % filename
+
+
+Third-party domains
+-------------------
+
+Support for other domains can be added by extensions with
+:py:func:`.add_linkcode_domain()`.
+For example, a Sphinx extension that provides a ``php`` domain
+could use the following code to support :mod:`~sphinx.ext.linkcode`:
+
+.. code-block:: python
+
+   from sphinx.ext.linkcode import add_linkcode_domain
+
+   def setup(app):
+       add_linkcode_domain('php', ['namespace', 'class', 'fullname'])
+
+.. autofunction:: add_linkcode_domain

sphinx/ext/linkcode.py

@@ -18,6 +18,23 @@ if TYPE_CHECKING:
     from sphinx.util.typing import ExtensionMetadata
 
 
+_DOMAIN_KEYS = {
+    'py': ['module', 'fullname'],
+    'c': ['names'],
+    'cpp': ['names'],
+    'js': ['object', 'fullname'],
+}
+
+
+def add_linkcode_domain(domain: str, keys: list[str], override: bool = False) -> None:
+    """Register a new list of keys to use for a domain.
+
+    .. versionadded:: 8.2
+    """
+    if override or domain not in _DOMAIN_KEYS:
+        _DOMAIN_KEYS[domain] = list(keys)
+
+
 class LinkcodeError(SphinxError):
     category = 'linkcode error'
 
@@ -37,13 +54,6 @@ def doctree_read(app: Sphinx, doctree: Node) -> None:
     # ``supported_linkcode`` attribute.
     node_only_expr = getattr(app.builder, 'supported_linkcode', 'html')
 
-    domain_keys = {
-        'py': ['module', 'fullname'],
-        'c': ['names'],
-        'cpp': ['names'],
-        'js': ['object', 'fullname'],
-    }
-
     for objnode in list(doctree.findall(addnodes.desc)):
         domain = objnode.get('domain')
         uris: set[str] = set()
@@ -53,7 +63,7 @@ def doctree_read(app: Sphinx, doctree: Node) -> None:
 
             # Convert signode to a specified format
             info = {}
-            for key in domain_keys.get(domain, []):
+            for key in _DOMAIN_KEYS.get(domain, []):
                 value = signode.get(key)
                 if not value:
                     value = ''

tests/roots/test-ext-viewcode/conf.py

@@ -1,6 +1,8 @@
 import sys
 from pathlib import Path
 
+from sphinx.ext.linkcode import add_linkcode_domain
+
 sys.path.insert(0, str(Path.cwd().resolve()))
 
 extensions = ['sphinx.ext.autodoc', 'sphinx.ext.viewcode']
@@ -19,5 +21,10 @@ if 'test_linkcode' in tags:  # NoQA: F821 (tags is injected into conf.py)
             return 'https://foobar/js/' + info['fullname']
         elif domain in {'c', 'cpp'}:
             return f'https://foobar/{domain}/{"".join(info["names"])}'
+        elif domain == 'rst':
+            return 'http://foobar/rst/{fullname}'.format(**info)
         else:
             raise AssertionError
+
+    def setup(app):
+        add_linkcode_domain('rst', ['fullname'])

tests/roots/test-ext-viewcode/objects.rst

@@ -167,3 +167,10 @@ CPP domain
 
    .. cpp:function:: T& operator[]( unsigned j )
                      const T& operator[]( unsigned j ) const
+
+rST domain
+==========
+
+.. rst:role:: foo
+
+   Foo description.

tests/test_extensions/test_ext_viewcode.py

@@ -116,6 +116,7 @@ def test_linkcode(app):
     assert 'https://foobar/js/' in stuff
     assert 'https://foobar/c/' in stuff
     assert 'https://foobar/cpp/' in stuff
+    assert 'http://foobar/rst/' in stuff
 
 
 @pytest.mark.sphinx('html', testroot='ext-viewcode-find', freshenv=True)