RefExpr in determining model fullname not supported

mypy_django_plugin/plugins/migrations.py

@@ -1,16 +1,30 @@
-from typing import cast
+from typing import cast, Optional
 
 from mypy.checker import TypeChecker
-from mypy.nodes import TypeInfo
+from mypy.nodes import TypeInfo, Expression, StrExpr, NameExpr, RefExpr, Var
 from mypy.plugin import MethodContext
 from mypy.types import Type, Instance, TypeType
 
 from mypy_django_plugin import helpers
 
 
+def get_string_value_from_expr(expr: Expression) -> Optional[str]:
+    if isinstance(expr, StrExpr):
+        return expr.value
+    # TODO: somehow figure out other cases
+    return None
+
+
 def determine_model_cls_from_string_for_migrations(ctx: MethodContext) -> Type:
-    app_label = ctx.args[ctx.callee_arg_names.index('app_label')][0].value
+    app_label_expr = ctx.args[ctx.callee_arg_names.index('app_label')][0]
-    model_name = ctx.args[ctx.callee_arg_names.index('model_name')][0].value
+    app_label = get_string_value_from_expr(app_label_expr)
+    if app_label is None:
+        return ctx.default_return_type
+
+    model_name_expr = ctx.args[ctx.callee_arg_names.index('model_name')][0]
+    model_name = get_string_value_from_expr(model_name_expr)
+    if model_name is None:
+        return ctx.default_return_type
 
     api = cast(TypeChecker, ctx.api)
     model_fullname = helpers.get_model_fullname(app_label, model_name, all_modules=api.modules)

test-data/typecheck/migrations.test

@@ -8,6 +8,23 @@ model_cls = apps.get_model('myapp', 'User')
 reveal_type(model_cls)  # E: Revealed type is 'Type[myapp.models.User]'
 reveal_type(model_cls.objects)  # E: Revealed type is 'django.db.models.manager.Manager[myapp.models.User]'
 
+[file myapp/__init__.py]
+[file myapp/models.py]
+from django.db import models
+class User(models.Model):
+    pass
+
+[CASE registry_apps_get_model_passed_as_variables_not_supported]
+from django.apps.registry import Apps
+from typing import TYPE_CHECKING
+if TYPE_CHECKING:
+    from myapp.models import User
+app_name = 'myapp'
+model_name = 'User'
+apps = Apps()
+model_cls = apps.get_model(app_name, model_name)
+reveal_type(model_cls)  # E: Revealed type is 'Type[django.db.models.base.Model]'
+
 [file myapp/__init__.py]
 [file myapp/models.py]
 from django.db import models