fix(docs): add workaround for sphinx TypeVar bug

sphinx-doc/sphinx#10974

doc/src/conf.py

@@ -530,3 +530,21 @@ def linkcode_resolve(domain, info):
 
     fn = os.path.relpath(fn, start=os.path.dirname(sympy.__file__))
     return blobpath + fn + linespec
+
+
+def resolve_type_aliases(app, env, node, contnode):
+    """Resolve :class: references to our type aliases as :attr: instead."""
+    # A sphinx bug means that TypeVar doesn't work:
+    # https://github.com/sphinx-doc/sphinx/issues/10785
+    if (
+        node["refdomain"] == "py"
+        and node["reftype"] == "class"
+        and node["reftarget"] in ["sympy.utilities.decorator.T"]
+    ):
+        return app.env.get_domain("py").resolve_xref(
+            env, node["refdoc"], app.builder, "attr", node["reftarget"], node, contnode
+        )
+
+
+def setup(app):
+    app.connect("missing-reference", resolve_type_aliases)

sympy/utilities/decorator.py

@@ -9,7 +9,8 @@
 from sympy.utilities.exceptions import sympy_deprecation_warning
 
 
-_T = TypeVar('_T')
+T = TypeVar('T')
+"""A generic type"""
 
 
 def threaded_factory(func, use_add):
@@ -180,7 +181,7 @@ def depends_on_deco(fn):
     return depends_on_deco
 
 
-def public(obj: _T) -> _T:
+def public(obj: T) -> T:
     """
     Append ``obj``'s name to global ``__all__`` variable (call site).