don't report warn-redundant-cast to cast of Union of Any

Author: asottile

mypy/checkexpr.py

@@ -4687,7 +4687,7 @@ def visit_cast_expr(self, expr: CastExpr) -> Type:
         options = self.chk.options
         if (
             options.warn_redundant_casts
-            and not isinstance(get_proper_type(target_type), AnyType)
+            and not is_same_type(target_type, AnyType(TypeOfAny.special_form))
             and is_same_type(source_type, target_type)
         ):
             self.msg.redundant_cast(target_type, expr)

test-data/unit/check-warnings.test

@@ -57,6 +57,17 @@ cast(int, 1)
 [out]
 main:4: error: Redundant cast to "int"
 
+[case testCastFromUnionOfAnyOk]
+# flags: --warn-redundant-casts
+from typing import Any, cast, Union
+
+x = Any
+y = Any
+z = Any
+
+def f(q: Union[x, y, z]) -> None:
+    cast(Union[x, y], q)
+
 -- Unused 'type: ignore' comments
 -- ------------------------------