Fixed false positives for function stubs (#2927)

Close #1581

7 files changed, 127 insertions, 35 deletions

diff --git a/ChangeLog b/ChangeLog
index 9ad2a79b6..5afba3ebc 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -147,6 +147,10 @@ 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?
 ===========================
diff --git a/pylint/checkers/base.py b/pylint/checkers/base.py
index e9aecb287..76ef09608 100644
--- a/pylint/checkers/base.py
+++ b/pylint/checkers/base.py
@@ -836,7 +836,15 @@ class BasicErrorChecker(_BasicChecker):
     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)
+            ),
+            node,
+        )
         if defined_self is not node and not astroid.are_exclusive(node, defined_self):
 
             # Additional checks for methods which are not considered
@@ -847,6 +855,9 @@ class BasicErrorChecker(_BasicChecker):
             ):
                 return
 
+            if utils.is_overload_stub(node):
+                return
+
             dummy_variables_rgx = lint_utils.get_global_option(
                 self, "dummy-variables-rgx", default=None
             )
diff --git a/pylint/checkers/utils.py b/pylint/checkers/utils.py
index 2f7402892..826181845 100644
--- a/pylint/checkers/utils.py
+++ b/pylint/checkers/utils.py
@@ -1225,3 +1225,15 @@ 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"]
+    )
diff --git a/pylint/checkers/variables.py b/pylint/checkers/variables.py
index 4ae13cadf..26cb94555 100644
--- a/pylint/checkers/variables.py
+++ b/pylint/checkers/variables.py
@@ -968,6 +968,45 @@ class VariablesChecker(BaseChecker):
             regex = authorized_rgx
         return regex and regex.match(name)
 
+    def _check_unused_arguments(self, name, node, stmt, argnames):
+        is_method = node.is_method()
+        klass = node.parent.frame()
+        if is_method and isinstance(klass, astroid.ClassDef):
+            confidence = (
+                INFERENCE if utils.has_known_bases(klass) else INFERENCE_FAILURE
+            )
+        else:
+            confidence = HIGH
+
+        if is_method:
+            # Don't warn for the first argument of a (non static) method
+            if node.type != "staticmethod" and name == argnames[0]:
+                return
+            # Don't warn for argument of an overridden method
+            overridden = overridden_method(klass, node.name)
+            if overridden is not None and name in overridden.argnames():
+                return
+            if node.name in utils.PYMETHODS and node.name not in (
+                "__init__",
+                "__new__",
+            ):
+                return
+        # Don't check callback arguments
+        if any(
+            node.name.startswith(cb) or node.name.endswith(cb)
+            for cb in self.config.callbacks
+        ):
+            return
+        # 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.is_overload_stub(node):
+            return
+
+        self.add_message("unused-argument", args=name, node=stmt, confidence=confidence)
+
     def _check_is_unused(self, name, node, stmt, global_names, nonlocal_names):
         # pylint: disable=too-many-branches
         # Ignore some special names specified by user configuration.
@@ -991,42 +1030,9 @@ class VariablesChecker(BaseChecker):
         argnames = list(
             itertools.chain(node.argnames(), [arg.name for arg in node.args.kwonlyargs])
         )
-        is_method = node.is_method()
-        klass = node.parent.frame()
-        if is_method and isinstance(klass, astroid.ClassDef):
-            confidence = (
-                INFERENCE if utils.has_known_bases(klass) else INFERENCE_FAILURE
-            )
-        else:
-            confidence = HIGH
-
         # Care about functions with unknown argument (builtins)
         if name in argnames:
-            if is_method:
-                # Don't warn for the first argument of a (non static) method
-                if node.type != "staticmethod" and name == argnames[0]:
-                    return
-                # Don't warn for argument of an overridden method
-                overridden = overridden_method(klass, node.name)
-                if overridden is not None and name in overridden.argnames():
-                    return
-                if node.name in utils.PYMETHODS and node.name not in (
-                    "__init__",
-                    "__new__",
-                ):
-                    return
-            # Don't check callback arguments
-            if any(
-                node.name.startswith(cb) or node.name.endswith(cb)
-                for cb in self.config.callbacks
-            ):
-                return
-            # Don't check arguments of singledispatch.register function.
-            if utils.is_registered_in_singledispatch_function(node):
-                return
-            self.add_message(
-                "unused-argument", args=name, node=stmt, confidence=confidence
-            )
+            self._check_unused_arguments(name, node, stmt, argnames)
         else:
             if stmt.parent and isinstance(
                 stmt.parent, (astroid.Assign, astroid.AnnAssign)
@@ -1069,6 +1075,11 @@ class VariablesChecker(BaseChecker):
                     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):
diff --git a/pylint/test/functional/typing_use.py b/pylint/test/functional/typing_use.py
new file mode 100644
index 000000000..3e2c48ba0
--- /dev/null
+++ b/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
diff --git a/pylint/test/functional/typing_use.rc b/pylint/test/functional/typing_use.rc
new file mode 100644
index 000000000..0ba2b6333
--- /dev/null
+++ b/pylint/test/functional/typing_use.rc
@@ -0,0 +1,2 @@
+[testoptions]
+min_pyver=3.6
diff --git a/pylint/test/functional/typing_use.txt b/pylint/test/functional/typing_use.txt
new file mode 100644
index 000000000..1d0233c98
--- /dev/null
+++ b/pylint/test/functional/typing_use.txt
@@ -0,0 +1 @@
+function-redefined:21:double_with_docstring:"function already defined line 16"