Emit used-before-assignment for further imports guarded by TYPE_CHECKING (#7806)

Previously, this message was only emitted for imports guarded directly under
TYPE_CHECKING, not guarded two if-branches deep, nor when TYPE_CHECKING
was imported from typing under an alias.

Author: jacobtylerwalls

doc/whatsnew/fragments/7539.false_negative

@@ -0,0 +1,7 @@
+Emit ``used-before-assignment`` for further imports guarded by ``TYPE_CHECKING``
+
+Previously, this message was only emitted for imports guarded directly under
+``TYPE_CHECKING``, not guarded two if-branches deep, nor when ``TYPE_CHECKING``
+was imported from ``typing`` under an alias.
+
+Closes #7539

pylint/checkers/variables.py

@@ -28,12 +28,7 @@
     in_type_checking_block,
     is_postponed_evaluation_enabled,
 )
-from pylint.constants import (
-    PY39_PLUS,
-    TYPING_NEVER,
-    TYPING_NORETURN,
-    TYPING_TYPE_CHECKS_GUARDS,
-)
+from pylint.constants import PY39_PLUS, TYPING_NEVER, TYPING_NORETURN
 from pylint.interfaces import CONTROL_FLOW, HIGH, INFERENCE, INFERENCE_FAILURE
 from pylint.typing import MessageDefinitionTuple
 
@@ -2201,7 +2196,7 @@ def _is_variable_violation(
             if (
                 isinstance(defstmt, (nodes.Import, nodes.ImportFrom))
                 and isinstance(defstmt.parent, nodes.If)
-                and defstmt.parent.test.as_string() in TYPING_TYPE_CHECKS_GUARDS
+                and in_type_checking_block(defstmt)
             ):
                 defstmt_parent = defstmt.parent
 

pylint/constants.py

@@ -99,9 +99,6 @@ class WarningScope:
 )
 
 
-TYPING_TYPE_CHECKS_GUARDS = frozenset({"typing.TYPE_CHECKING", "TYPE_CHECKING"})
-
-
 def _warn_about_old_home(pylint_home: pathlib.Path) -> None:
     """Warn users about the old pylint home being deprecated.
 

tests/functional/u/used/used_before_assignment_typing.py

@@ -5,6 +5,8 @@
 from typing import List, Optional, TYPE_CHECKING
 
 if TYPE_CHECKING:
+    if True:  # pylint: disable=using-constant-test
+        import math
     import datetime
 
 class MyClass:
@@ -78,6 +80,15 @@ def other_function(self) -> None:
         _x: MyThirdClass = self
 
 
+class MyFourthClass:  # pylint: disable=too-few-public-methods
+    """Class to test conditional imports guarded by TYPE_CHECKING two levels
+    up then used in function annotation. See https://github.com/PyCQA/pylint/issues/7539"""
+
+    def is_close(self, comparator: math.isclose, first, second):  # [used-before-assignment]
+        """Conditional imports guarded are only valid for variable annotations."""
+        comparator(first, second)
+
+
 class VariableAnnotationsGuardedByTypeChecking:  # pylint: disable=too-few-public-methods
     """Class to test conditional imports guarded by TYPE_CHECKING then used in
     local (function) variable annotations, which are not evaluated at runtime.

tests/functional/u/used/used_before_assignment_typing.txt

@@ -1,4 +1,5 @@
-undefined-variable:14:21:14:28:MyClass.incorrect_typing_method:Undefined variable 'MyClass':UNDEFINED
-undefined-variable:19:26:19:33:MyClass.incorrect_nested_typing_method:Undefined variable 'MyClass':UNDEFINED
-undefined-variable:24:20:24:27:MyClass.incorrect_default_method:Undefined variable 'MyClass':UNDEFINED
-used-before-assignment:88:20:88:28:VariableAnnotationsGuardedByTypeChecking:Using variable 'datetime' before assignment:HIGH
+undefined-variable:16:21:16:28:MyClass.incorrect_typing_method:Undefined variable 'MyClass':UNDEFINED
+undefined-variable:21:26:21:33:MyClass.incorrect_nested_typing_method:Undefined variable 'MyClass':UNDEFINED
+undefined-variable:26:20:26:27:MyClass.incorrect_default_method:Undefined variable 'MyClass':UNDEFINED
+used-before-assignment:87:35:87:39:MyFourthClass.is_close:Using variable 'math' before assignment:HIGH
+used-before-assignment:99:20:99:28:VariableAnnotationsGuardedByTypeChecking:Using variable 'datetime' before assignment:HIGH