Use infer_condition_value to detect TYPE_CHECKING.

Author: tyralla

mypy/checker.py

@@ -152,6 +152,7 @@
 from mypy.patterns import AsPattern, StarredPattern
 from mypy.plugin import Plugin
 from mypy.plugins import dataclasses as dataclasses_plugin
+from mypy.reachability import infer_condition_value, MYPY_TRUE, MYPY_FALSE
 from mypy.scope import Scope
 from mypy.semanal import is_trivial_body, refers_to_fullname, set_callable_name
 from mypy.semanal_enum import ENUM_BASES, ENUM_SPECIAL_PROPS
@@ -5045,7 +5046,7 @@ def _visit_if_stmt_redundant_expr_helper(
 
         if codes.REDUNDANT_EXPR not in self.options.enabled_error_codes:
             return
-        if refers_to_fullname(expr, ("typing.TYPE_CHECKING", "typing_extensions.TYPE_CHECKING")):
+        if infer_condition_value(expr, self.options) in (MYPY_FALSE, MYPY_TRUE):
             return
 
         def _filter(body: Block | None) -> bool:

test-data/unit/check-isinstance.test

@@ -3080,6 +3080,16 @@ while False:  # E: While condition is always false
 
 [builtins fixtures/bool.pyi]
 
+[case testNoRedundantExpressionWarningsForUsagesOfTYPECHECKING]
+# flags: --enable-error-code=redundant-expr
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    ...
+
+if not TYPE_CHECKING:
+    ...
+
 [case testNoRedundantExpressionWarningsForExhaustivenessChecks]
 # flags: --enable-error-code=redundant-expr
 from typing import Literal, Never, NoReturn