Fix crash when showing partially analyzed type in error message (#17961)

Fixes #17954

People say something about cache invalidation being one of the hardest
problems...

mypy/semanal.py

@@ -3958,8 +3958,10 @@ def check_and_set_up_type_alias(self, s: AssignmentStmt) -> bool:
         # so we need to replace it with non-explicit Anys.
         res = make_any_non_explicit(res)
         if self.options.disallow_any_unimported and has_any_from_unimported_type(res):
-            self.msg.unimported_type_becomes_any("Type alias target", res, s)
-            res = make_any_non_unimported(res)
+            # Only show error message once, when the type is fully analyzed.
+            if not has_placeholder(res):
+                self.msg.unimported_type_becomes_any("Type alias target", res, s)
+                res = make_any_non_unimported(res)
         # Note: with the new (lazy) type alias representation we only need to set no_args to True
         # if the expected number of arguments is non-zero, so that aliases like `A = List` work
         # but not aliases like `A = TypeAliasType("A", List)` as these need explicit type params.
@@ -4013,6 +4015,8 @@ def check_and_set_up_type_alias(self, s: AssignmentStmt) -> bool:
                     existing.node.alias_tvars = alias_tvars
                     existing.node.no_args = no_args
                     updated = True
+                    # Invalidate recursive status cache in case it was previously set.
+                    existing.node._is_recursive = None
             else:
                 # Otherwise just replace existing placeholder with type alias.
                 existing.node = alias_node

test-data/unit/check-recursive-types.test

@@ -1006,3 +1006,11 @@ ta: Tuple[A]
 p: Proto
 p = ta
 [builtins fixtures/tuple.pyi]
+
+[case testRecursiveAliasesWithAnyUnimported]
+# flags: --disallow-any-unimported
+from typing import Callable
+from bogus import Foo  # type: ignore
+
+A = Callable[[Foo, "B"], Foo]  # E: Type alias target becomes "Callable[[Any, B], Any]" due to an unfollowed import
+B = Callable[[Foo, A], Foo]  # E: Type alias target becomes "Callable[[Any, A], Any]" due to an unfollowed import