Handle class decorators during typing checks.

5 files changed, 77 insertions, 2 deletions

diff --git a/CONTRIBUTORS.txt b/CONTRIBUTORS.txt
index 702af289a..e4cd248f4 100644
--- a/CONTRIBUTORS.txt
+++ b/CONTRIBUTORS.txt
@@ -427,3 +427,5 @@ contributors:
 * Takashi Hirashima: contributor
 
 * Joffrey Mander: contributor
+
+* Julien Palard: contributor
diff --git a/ChangeLog b/ChangeLog
index fff8ec92f..d2625bc2e 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -2,6 +2,10 @@
 Pylint's ChangeLog
 ------------------
 
+* Handle class decorators applied to function.
+
+  Closes #3882
+
 * Add check for empty comments
 
 * Fix minor documentation issue in contribute.rst
diff --git a/doc/development_guide/contribute.rst b/doc/development_guide/contribute.rst
index 0476c197c..f82bc442c 100644
--- a/doc/development_guide/contribute.rst
+++ b/doc/development_guide/contribute.rst
@@ -110,7 +110,10 @@ your patch gets accepted.
   (`What's New` section). For the release document we usually write some more details,
   and it is also a good place to offer examples on how the new change is supposed to work.
 
-- Add yourself to the `CONTRIBUTORS` file, if you are not already there.
+- Add a short entry in :file:`doc/whatsnew/VERSION.rst`.
+
+- Add yourself to the `CONTRIBUTORS` file, flag youself appropriately
+  (if in doubt, you're a ``contributor``).
 
 - Write a comprehensive commit message
 
diff --git a/pylint/checkers/typecheck.py b/pylint/checkers/typecheck.py
index 0e669ec33..17dcd50c2 100644
--- a/pylint/checkers/typecheck.py
+++ b/pylint/checkers/typecheck.py
@@ -65,7 +65,7 @@ import astroid
 import astroid.arguments
 import astroid.context
 import astroid.nodes
-from astroid import bases, decorators, exceptions, modutils, objects
+from astroid import bases, decorators, exceptions, helpers, modutils, objects
 from astroid.interpreter import dunder_lookup
 
 from pylint.checkers import BaseChecker, utils
@@ -1720,9 +1720,18 @@ accessed. Python regular expressions are accepted.",
             return
 
         inferred = safe_infer(node.value)
+
         if inferred is None or inferred is astroid.Uninferable:
             return
 
+        if inferred.decorators:
+            first_decorator = helpers.safe_infer(inferred.decorators.nodes[0])
+            if isinstance(first_decorator, astroid.ClassDef):
+                inferred = first_decorator.instantiate_class()
+            else:
+                return  # It would be better to handle function
+                # decorators, but let's start slow.
+
         if not supported_protocol(inferred):
             self.add_message(msg, args=node.value.as_string(), node=node.value)
 
diff --git a/tests/checkers/unittest_typecheck.py b/tests/checkers/unittest_typecheck.py
index 346f5f38d..500ae60d9 100644
--- a/tests/checkers/unittest_typecheck.py
+++ b/tests/checkers/unittest_typecheck.py
@@ -24,6 +24,7 @@ import astroid
 import pytest
 
 from pylint.checkers import typecheck
+from pylint.interfaces import UNDEFINED
 from pylint.testutils import CheckerTestCase, Message, set_config
 
 try:
@@ -286,6 +287,62 @@ class TestTypeChecker(CheckerTestCase):
         with self.assertNoMessages():
             self.checker.visit_subscript(subscript)
 
+    def test_typing_option_object_is_subscriptable_issue3882(self):
+        module = astroid.parse(
+            """
+        import typing
+        test = typing.Optional[int]
+        """
+        )
+        subscript = module.body[-1].value
+        with self.assertNoMessages():
+            self.checker.visit_subscript(subscript)
+
+    def test_decorated_by_a_subscriptable_class_issue3882(self):
+        module = astroid.parse(
+            """
+        class Deco:
+            def __init__(self, f):
+                self.f = f
+
+            def __getitem__(self, item):
+                return item
+        @Deco
+        def decorated():
+            ...
+
+        test = decorated[None]
+        """
+        )
+        subscript = module.body[-1].value
+        with self.assertNoMessages():
+            self.checker.visit_subscript(subscript)
+
+    def test_decorated_by_an_unsubscriptable_class_issue3882(self):
+        module = astroid.parse(
+            """
+        class Deco:
+            def __init__(self, f):
+                self.f = f
+
+        @Deco
+        def decorated():
+            ...
+
+        test = decorated[None]
+        """
+        )
+        subscript = module.body[-1].value
+        with self.assertAddsMessages(
+            Message(
+                "unsubscriptable-object",
+                node=subscript.value,
+                args="decorated",
+                confidence=UNDEFINED,
+            )
+        ):
+            self.checker.visit_subscript(subscript)
+
     def test_staticmethod_multiprocessing_call(self):
         """Make sure not-callable isn't raised for descriptors