Fix redundant-expr error code

Author: JukkaL

mypy/checker.py

@@ -618,6 +618,9 @@ def accept_loop(
                 self.options.enabled_error_codes.add(codes.REDUNDANT_EXPR)
             if warn_unreachable or warn_redundant:
                 with self.binder.frame_context(can_skip=True, break_frame=2, continue_frame=1):
+                    if on_enter_body is not None:
+                        on_enter_body()
+
                     self.accept(body)
 
             # If exit_condition is set, assume it must be False on exit from the loop:

test-data/unit/check-inference.test

@@ -3895,7 +3895,17 @@ foo = [
 reveal_type(foo)  # N: Revealed type is "builtins.list[Tuple[builtins.int, typing.Sequence[builtins.str]]]"
 [builtins fixtures/tuple.pyi]
 
-[case testForLoopIndexVaribaleNarrowing]
+[case testForLoopIndexVaribaleNarrowing1]
+# flags: --local-partial-types
+from typing import Union
+x: Union[int, str]
+x = "abc"
+for x in list[int]():
+    reveal_type(x)  # N: Revealed type is "builtins.int"
+reveal_type(x) # N: Revealed type is "Union[builtins.int, builtins.str]"
+
+[case testForLoopIndexVaribaleNarrowing2]
+# flags: --enable-error-code=redundant-expr
 from typing import Union
 x: Union[int, str]
 x = "abc"