Fix crash on unimported Any with Required/NotRequired

Fixes python#17604; fixes python#17608.  (To reproduce the crash without mypyc,
replace `cast(ProperType, typ)` with an assertion in
`get_proper_type`.)

Signed-off-by: Anders Kaseorg <andersk@mit.edu>

mypy/checker.py

@@ -198,6 +198,7 @@
     Overloaded,
     PartialType,
     ProperType,
+    RequiredType,
     TupleType,
     Type,
     TypeAliasType,
@@ -2945,7 +2946,11 @@ def visit_assignment_stmt(self, s: AssignmentStmt) -> None:
                     "A type on this line", AnyType(TypeOfAny.special_form), s
                 )
             else:
-                self.msg.unimported_type_becomes_any("Type of variable", s.type, s)
+                self.msg.unimported_type_becomes_any(
+                    "Type of variable",
+                    s.type.item if isinstance(s.type, RequiredType) else s.type,
+                    s,
+                )
         check_for_explicit_any(s.type, self.options, self.is_typeshed_stub, self.msg, context=s)
 
         if len(s.lvalues) > 1:

test-data/unit/check-typeddict.test

@@ -2394,6 +2394,14 @@ class ForceDeferredEval: pass
 [builtins fixtures/dict.pyi]
 [typing fixtures/typing-typeddict.pyi]
 
+[case testTypedDictRequiredUnimportedAny]
+# flags: --disallow-any-unimported
+from typing import NotRequired, TypedDict
+from nonexistent import Foo  # type: ignore[import-not-found]
+class Bar(TypedDict):
+    foo: NotRequired[Foo]  # E: Type of variable becomes "Any" due to an unfollowed import
+[typing fixtures/typing-typeddict.pyi]
+
 -- Required[]
 
 [case testDoesRecognizeRequiredInTypedDictWithClass]