Don't warn about returning Any if it is a proper subtype of the retur…

…n type (#3473)

Fixes #3472

mypy/checker.py

@@ -1874,7 +1874,8 @@ def check_return_stmt(self, s: ReturnStmt) -> None:
                 if isinstance(typ, AnyType):
                     # (Unless you asked to be warned in that case, and the
                     # function is not declared to return Any)
-                    if not isinstance(return_type, AnyType) and self.options.warn_return_any:
+                    if (not is_proper_subtype(AnyType(), return_type) and
+                            self.options.warn_return_any):
                         self.warn(messages.RETURN_ANY.format(return_type), s)
                     return
 

test-data/unit/check-warnings.test

@@ -165,3 +165,20 @@ from typing import Any
 def g() -> Any: pass
 def f() -> Any: return g()
 [out]
+
+[case testOKReturnAnyIfProperSubtype]
+# flags: --warn-return-any --strict-optional
+from typing import Any, Optional
+
+class Test(object):
+
+    def __init__(self) -> None:
+        self.attr = "foo"  # type: Any
+
+    def foo(self, do_it: bool) -> Optional[Any]:
+        if do_it:
+            return self.attr  # Should not warn here
+        else:
+            return None
+[builtins fixtures/list.pyi]
+[out]