Fix infinite semantic analysis loop when using from_queryset (#2935)

When `create_manager_info_from_from_queryset_call()` returns `None`,
the code unconditionally called `add_symbol_table_node()` with a
`PlaceholderNode` on every iteration. This sets mypy's `progress = True`,
preventing the semantic analysis loop from terminating, resulting in
"maximum semantic analysis iteration count reached" error.

The fix checks if a `PlaceholderNode` already exists before adding a
new one, preventing redundant symbol table modifications that trigger
infinite iterations.

Fixes #2373

Author: lee3jjang

mypy_django_plugin/transformers/managers.py

@@ -334,9 +334,12 @@ def create_new_manager_class_from_from_queryset_method(ctx: DynamicClassDefConte
     new_manager_info = create_manager_info_from_from_queryset_call(semanal_api, ctx.call, ctx.name)
     if new_manager_info is None:
         if not ctx.api.final_iteration:
-            # XXX: hack for python/mypy#17402
-            ph = PlaceholderNode(ctx.api.qualified_name(ctx.name), ctx.call, ctx.call.line, becomes_typeinfo=True)
-            ctx.api.add_symbol_table_node(ctx.name, SymbolTableNode(GDEF, ph))
+            # Only add PlaceholderNode if it doesn't already exist to prevent
+            # infinite semantic analysis iterations (fixes #2373)
+            if not (manager_sym and isinstance(manager_sym.node, PlaceholderNode)):
+                # XXX: hack for python/mypy#17402
+                ph = PlaceholderNode(ctx.api.qualified_name(ctx.name), ctx.call, ctx.call.line, becomes_typeinfo=True)
+                ctx.api.add_symbol_table_node(ctx.name, SymbolTableNode(GDEF, ph))
             ctx.api.defer()
         return
 

tests/typecheck/managers/querysets/test_from_queryset.yml

@@ -999,3 +999,46 @@
                     field = models.CharField()
                     b = models.ForeignKey(B, on_delete=models.CASCADE)
                     objects = Manager()
+
+# Regression test for #2373: Ensure from_queryset handles repeated deferrals
+# correctly. When create_manager_info_from_from_queryset_call returns None due
+# to forward references, PlaceholderNode should only be added once, not on
+# every iteration.
+-   case: test_from_queryset_repeated_deferral_with_forward_metaclass
+    main: |
+        from typing_extensions import reveal_type
+        from myapp.models import MyModel
+        reveal_type(MyModel.objects.custom_method())
+    out: |
+        main:3: error: Access to generic instance variables via class is ambiguous  [misc]
+        main:3: note: Revealed type is "builtins.str"
+    mypy_config: |
+        [mypy.plugins.django-stubs]
+        django_settings_module = myapp
+    files:
+        -   path: myapp/__init__.py
+        -   path: myapp/models.py
+            content: |
+                from typing import TypeVar
+                from django.db import models
+                from django.db.models.manager import Manager
+
+                M = TypeVar("M", bound=models.Model, covariant=True)
+
+                # Forward reference to metaclass triggers deferral, causing
+                # create_manager_info_from_from_queryset_call to return None
+                # on initial passes. The fix ensures PlaceholderNode is not
+                # re-added on each iteration, preventing progress flag from
+                # being set repeatedly.
+                class CustomQuerySet(models.QuerySet[M], metaclass=ForwardMCS):
+                    def custom_method(self) -> str:
+                        return "test"
+
+                CustomManager = Manager.from_queryset(CustomQuerySet)
+
+                class MyModel(models.Model):
+                    objects = CustomManager()
+
+                # Forward-referenced metaclass defined after use
+                class ForwardMCS(type):
+                    pass