Support callables in Annotated types

CHANGES.rst

@@ -8,6 +8,9 @@ Bugs fixed
   Patch by Adam Turner.
 * #12620: Ensure that old-style object description options are respected.
   Patch by Adam Turner.
+* #12601, #12625: Support callable objects in :py:class:`~typing.Annotated` type
+  metadata in the Python domain.
+  Patch by Adam Turner.
 
 Release 7.4.6 (released Jul 18, 2024)
 =====================================

sphinx/domains/python/_annotations.py

@@ -161,7 +161,29 @@ def unparse(node: ast.AST) -> list[Node]:
                           addnodes.desc_sig_punctuation('', ')')]
 
             return result
-        raise SyntaxError  # unsupported syntax
+        if isinstance(node, ast.Call):
+            # Call nodes can be used in Annotated type metadata,
+            # for example Annotated[str, ArbitraryTypeValidator(str, len=10)]
+            args = []
+            for arg in node.args:
+                args += unparse(arg)
+                args.append(addnodes.desc_sig_punctuation('', ','))
+                args.append(addnodes.desc_sig_space())
+            for kwd in node.keywords:
+                args.append(addnodes.desc_sig_name(kwd.arg, kwd.arg))  # type: ignore[arg-type]
+                args.append(addnodes.desc_sig_operator('', '='))
+                args += unparse(kwd.value)
+                args.append(addnodes.desc_sig_punctuation('', ','))
+                args.append(addnodes.desc_sig_space())
+            result = [
+                *unparse(node.func),
+                addnodes.desc_sig_punctuation('', '('),
+                *args[:-2],  # skip the final comma and space
+                addnodes.desc_sig_punctuation('', ')'),
+            ]
+            return result
+        msg = f'unsupported syntax: {node}'
+        raise SyntaxError(msg)  # unsupported syntax
 
     def _unparse_pep_604_annotation(node: ast.Subscript) -> list[Node]:
         subscript = node.slice

tests/test_domains/test_domain_py.py

@@ -370,6 +370,27 @@ def test_parse_annotation(app):
                           [desc_sig_punctuation, "]"]))
     assert_node(doctree[0], pending_xref, refdomain="py", reftype="obj", reftarget="typing.Literal")
 
+    # Annotated type with callable gets parsed
+    doctree = _parse_annotation("Annotated[Optional[str], annotated_types.MaxLen(max_length=10)]", app.env)
+    assert_node(doctree, (
+        [pending_xref, 'Annotated'],
+        [desc_sig_punctuation, '['],
+        [pending_xref, 'str'],
+        [desc_sig_space, ' '],
+        [desc_sig_punctuation, '|'],
+        [desc_sig_space, ' '],
+        [pending_xref, 'None'],
+        [desc_sig_punctuation, ','],
+        [desc_sig_space, ' '],
+        [pending_xref, 'annotated_types.MaxLen'],
+        [desc_sig_punctuation, '('],
+        [desc_sig_name, 'max_length'],
+        [desc_sig_operator, '='],
+        [desc_sig_literal_number, '10'],
+        [desc_sig_punctuation, ')'],
+        [desc_sig_punctuation, ']'],
+    ))
+
 
 def test_parse_annotation_suppress(app):
     doctree = _parse_annotation("~typing.Dict[str, str]", app.env)
@@ -802,7 +823,22 @@ def test_function_pep_695(app):
                         [desc_sig_name, 'A'],
                         [desc_sig_punctuation, ':'],
                         desc_sig_space,
-                        [desc_sig_name, ([pending_xref, 'int | Annotated[int, ctype("char")]'])],
+                        [desc_sig_name, (
+                            [pending_xref, 'int'],
+                            [desc_sig_space, ' '],
+                            [desc_sig_punctuation, '|'],
+                            [desc_sig_space, ' '],
+                            [pending_xref, 'Annotated'],
+                            [desc_sig_punctuation, '['],
+                            [pending_xref, 'int'],
+                            [desc_sig_punctuation, ','],
+                            [desc_sig_space, ' '],
+                            [pending_xref, 'ctype'],
+                            [desc_sig_punctuation, '('],
+                            [desc_sig_literal_string, "'char'"],
+                            [desc_sig_punctuation, ')'],
+                            [desc_sig_punctuation, ']'],
+                        )],
                     )],
                     [desc_type_parameter, (
                         [desc_sig_operator, '*'],
@@ -987,7 +1023,7 @@ def test_class_def_pep_696(app):
     ('[T:(*Ts)|int]', '[T: (*Ts) | int]'),
     ('[T:(int|(*Ts))]', '[T: (int | (*Ts))]'),
     ('[T:((*Ts)|int)]', '[T: ((*Ts) | int)]'),
-    ('[T:Annotated[int,ctype("char")]]', '[T: Annotated[int, ctype("char")]]'),
+    ("[T:Annotated[int,ctype('char')]]", "[T: Annotated[int, ctype('char')]]"),
 ])
 def test_pep_695_and_pep_696_whitespaces_in_bound(app, tp_list, tptext):
     text = f'.. py:function:: f{tp_list}()'