Handle variables defined only under a type checking clause

These kind of variables will cause a runtime error, since the variable
will not be defined, unless we use the `annotations` future.

Close #3081

2 files changed, 12 insertions, 0 deletions

diff --git a/tests/functional/u/undefined_variable.py b/tests/functional/u/undefined_variable.py
index 59af47e19..619794573 100644
--- a/tests/functional/u/undefined_variable.py
+++ b/tests/functional/u/undefined_variable.py
@@ -245,3 +245,14 @@ def nonlocal_in_ifexp():
     fig = plt.figure()
     fig.canvas.mpl_connect('button_press_event', onclick)
     plt.show(block=True)
+
+
+# pylint: disable=wrong-import-position
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from datetime import datetime
+
+
+def func_should_fail(_dt: datetime):  # [used-before-assignment]
+    pass
diff --git a/tests/functional/u/undefined_variable.txt b/tests/functional/u/undefined_variable.txt
index bc935c12d..5f9ca9747 100644
--- a/tests/functional/u/undefined_variable.txt
+++ b/tests/functional/u/undefined_variable.txt
@@ -24,3 +24,4 @@ undefined-variable:161::Undefined variable 'unicode_2'
 undefined-variable:171::Undefined variable 'unicode_4'
 undefined-variable:226:LambdaClass4.<lambda>:Undefined variable 'LambdaClass4'
 undefined-variable:234:LambdaClass5.<lambda>:Undefined variable 'LambdaClass5'
+used-before-assignment:257:func_should_fail:Using variable 'datetime' before assignment