From a5e9b0b7fe5f2b5e3b3efac844216159a24ebd9c Mon Sep 17 00:00:00 2001
From: Ivan Levkivskyi <levkivskyi@gmail.com>
Date: Wed, 16 Oct 2024 15:36:09 +0100
Subject: [PATCH] Fix crash when showing partially analyzed type in error
 message (#17961)

Fixes https://github.com/python/mypy/issues/17954

People say something about cache invalidation being one of the hardest
problems...
---
 mypy/semanal.py                           | 8 ++++++--
 test-data/unit/check-recursive-types.test | 8 ++++++++
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/mypy/semanal.py b/mypy/semanal.py
index 27abf2c1dc4c..00383c010dc9 100644
--- a/mypy/semanal.py
+++ b/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
diff --git a/test-data/unit/check-recursive-types.test b/test-data/unit/check-recursive-types.test
index ac1ea0c0035a..4d7af98204fb 100644
--- a/test-data/unit/check-recursive-types.test
+++ b/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