use is_same_type when determining if a cast is redundant

Author: asottile

mypy/checkexpr.py

@@ -4688,7 +4688,7 @@ def visit_cast_expr(self, expr: CastExpr) -> Type:
         if (
             options.warn_redundant_casts
             and not isinstance(get_proper_type(target_type), AnyType)
-            and source_type == target_type
+            and is_same_type(source_type, target_type)
         ):
             self.msg.redundant_cast(target_type, expr)
         if options.disallow_any_unimported and has_any_from_unimported_type(target_type):

test-data/unit/check-warnings.test

@@ -42,6 +42,21 @@ a: Any
 b = cast(Any, a)
 [builtins fixtures/list.pyi]
 
+[case testCastToObjectNotRedunant]
+# flags: --warn-redundant-casts
+from typing import cast
+
+a = 1
+b = cast(object, 1)
+
+[case testCastFromLiteralRedundant]
+# flags: --warn-redundant-casts
+from typing import cast
+
+cast(int, 1)
+[out]
+main:4: error: Redundant cast to "int"
+
 -- Unused 'type: ignore' comments
 -- ------------------------------