Support forward references for function-redefined check.

Close #2540

ChangeLog

@@ -7,6 +7,10 @@ What's New in Pylint 2.4.0?
 
 Release date: TBA
 
+* Support forward references for ``function-redefined`` check.
+
+  Close #2540
+
 * Added a new check, ``consider-using-sys-exit``
 
   This check is emitted when we detect that a quit() or exit() is invoked

pylint/checkers/base.py

@@ -171,6 +171,7 @@ def get_regex(cls, name_type):
 COMPARISON_OPERATORS = frozenset(("==", "!=", "<", ">", "<=", ">="))
 # List of methods which can be redefined
 REDEFINABLE_METHODS = frozenset(("__module__",))
+TYPING_FORWARD_REF_QNAME = "typing.ForwardRef"
 
 
 def _redefines_import(node):
@@ -820,13 +821,11 @@ def _check_in_loop(self, node, node_name):
     def _check_redefinition(self, redeftype, node):
         """check for redefinition of a function / method / class name"""
         parent_frame = node.parent.frame()
+
         # Ignore function stubs created for type information
+        redefinitions = parent_frame.locals[node.name]
         defined_self = next(
-            (
-                local
-                for local in parent_frame.locals[node.name]
-                if not utils.is_overload_stub(local)
-            ),
+            (local for local in redefinitions if not utils.is_overload_stub(local)),
             node,
         )
         if defined_self is not node and not astroid.are_exclusive(node, defined_self):
@@ -842,6 +841,16 @@ def _check_redefinition(self, redeftype, node):
             if utils.is_overload_stub(node):
                 return
 
+            # Check if we have forward references for this node.
+            for redefinition in redefinitions[: redefinitions.index(node)]:
+                inferred = utils.safe_infer(redefinition)
+                if (
+                    inferred
+                    and isinstance(inferred, astroid.Instance)
+                    and inferred.qname() == TYPING_FORWARD_REF_QNAME
+                ):
+                    return
+
             dummy_variables_rgx = lint_utils.get_global_option(
                 self, "dummy-variables-rgx", default=None
             )

tests/functional/f/function_redefined_2540.py

@@ -0,0 +1,9 @@
+# pylint: disable=missing-module-docstring,missing-class-docstring,too-few-public-methods,invalid-name
+
+from typing import ForwardRef
+
+Cls = ForwardRef("Cls")
+
+
+class Cls:
+    pass

tests/functional/f/function_redefined_2540.rc

@@ -0,0 +1,2 @@
+[testoptions]
+min_pyver=3.7