Fixed false positives for function stubs

Close #1581

ChangeLog

@@ -122,6 +122,11 @@ Release date: TBA
 
   Close #202
 
+* Fixed `unused-argument` and `function-redefined` getting raised for
+  functions decorated with `typing.overload`.
+
+  Close #1581
+
 What's New in Pylint 2.3.0?
 ===========================
 

pylint/checkers/base.py

@@ -836,7 +836,12 @@ 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()
-        defined_self = parent_frame[node.name]
+        # Ignore function stubs created for type information
+        defined_self = next(
+            local
+            for local in parent_frame.locals[node.name]
+            if not utils.is_overload_stub(local)
+        )
         if defined_self is not node and not astroid.are_exclusive(node, defined_self):
 
             # Additional checks for methods which are not considered
@@ -847,6 +852,9 @@ def _check_redefinition(self, redeftype, node):
             ):
                 return
 
+            if utils.is_overload_stub(node):
+                return
+
             dummy_variables_rgx = lint_utils.get_global_option(
                 self, "dummy-variables-rgx", default=None
             )

pylint/checkers/utils.py

@@ -1210,3 +1210,15 @@ def is_subclass_of(child: astroid.ClassDef, parent: astroid.ClassDef) -> bool:
         except _NonDeducibleTypeHierarchy:
             continue
     return False
+
+
+@lru_cache(maxsize=1024)
+def is_overload_stub(node: astroid.node_classes.NodeNG) -> bool:
+    """Check if a node if is a function stub decorated with typing.overload.
+
+    :param node: Node to check.
+    :returns: True if node is an overload function stub. False otherwise.
+    """
+    return isinstance(node, astroid.FunctionDef) and decorated_with(
+        node, ["typing.overload"]
+    )

pylint/checkers/variables.py

@@ -1026,6 +1026,11 @@ def _check_is_unused(self, name, node, stmt, global_names, nonlocal_names):
             # Don't check arguments of singledispatch.register function.
             if utils.is_registered_in_singledispatch_function(node):
                 return
+
+            # Don't check function stubs created only for type information
+            if utils.decorated_with(node, "typing.overload"):
+                return
+
             self.add_message(
                 "unused-argument", args=name, node=stmt, confidence=confidence
             )
@@ -1063,6 +1068,11 @@ def _check_is_unused(self, name, node, stmt, global_names, nonlocal_names):
                     self.add_message("unused-import", args=msg, node=stmt)
                     return
                 message_name = "unused-variable"
+
+            # Don't check function stubs created only for type information
+            if utils.is_overload_stub(node):
+                return
+
             self.add_message(message_name, args=name, node=stmt)
 
     def leave_functiondef(self, node):

pylint/test/functional/typing_use.py

@@ -0,0 +1,51 @@
+# pylint: disable=missing-docstring
+
+import typing
+
+
+@typing.overload
+def double_with_docstring(arg: str) -> str:
+    """Return arg, concatenated with itself."""
+
+
+@typing.overload
+def double_with_docstring(arg: int) -> int:
+    """Return twice arg."""
+
+
+def double_with_docstring(arg):
+    """Return 2 * arg."""
+    return 2 * arg
+
+
+def double_with_docstring(arg):  # [function-redefined]
+    """Redefined function implementation"""
+    return 2 * arg
+
+
+@typing.overload
+def double_with_ellipsis(arg: str) -> str:
+    ...
+
+
+@typing.overload
+def double_with_ellipsis(arg: int) -> int:
+    ...
+
+
+def double_with_ellipsis(arg):
+    return 2 * arg
+
+
+@typing.overload
+def double_with_pass(arg: str) -> str:
+    pass
+
+
+@typing.overload
+def double_with_pass(arg: int) -> int:
+    pass
+
+
+def double_with_pass(arg):
+    return 2 * arg

pylint/test/functional/typing_use.rc

@@ -0,0 +1,2 @@
+[testoptions]
+min_pyver=3.6

pylint/test/functional/typing_use.txt

@@ -0,0 +1 @@
+function-redefined:21:double_with_docstring:"function already defined line 16"