Fix used-before-assignment if conditional imports guarded again when used (#7980)

(cherry picked from commit e6f0bc5)

Author: jacobtylerwalls

doc/whatsnew/fragments/7979.false_positive

@@ -0,0 +1,4 @@
+Prevent ``used-before-assignment`` when imports guarded by ``if TYPE_CHECKING``
+are guarded again when used.
+
+Closes #7979

pylint/checkers/variables.py

@@ -27,12 +27,7 @@
     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
 
@@ -2003,7 +1998,8 @@ 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)
+                and not in_type_checking_block(node)
             ):
                 defstmt_parent = defstmt.parent
 

tests/functional/u/used/used_before_assignment_typing.py

@@ -6,6 +6,7 @@
 
 if TYPE_CHECKING:
     import datetime
+    from urllib.request import urlopen
 
 class MyClass:
     """Type annotation or default values for first level methods can't refer to their own class"""
@@ -90,3 +91,9 @@ class VariableAnnotationsGuardedByTypeChecking:  # pylint: disable=too-few-publi
     def print_date(self, date) -> None:
         date: datetime.date = date
         print(date)
+
+
+class ConditionalImportGuardedWhenUsed:  # pylint: disable=too-few-public-methods
+    """Conditional imports also guarded by TYPE_CHECKING when used."""
+    if TYPE_CHECKING:
+        print(urlopen)

tests/functional/u/used/used_before_assignment_typing.txt

@@ -1,4 +1,4 @@
-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:15:21:15:28:MyClass.incorrect_typing_method:Undefined variable 'MyClass':UNDEFINED
+undefined-variable:20:26:20:33:MyClass.incorrect_nested_typing_method:Undefined variable 'MyClass':UNDEFINED
+undefined-variable:25:20:25:27:MyClass.incorrect_default_method:Undefined variable 'MyClass':UNDEFINED
+used-before-assignment:89:20:89:28:VariableAnnotationsGuardedByTypeChecking:Using variable 'datetime' before assignment:HIGH