Fallback to checking kwargs of function call when looking for arguments of a call

mypy_django_plugin/lib/helpers.py

@@ -173,16 +173,22 @@ def get_class_fullname(klass: type) -> str:
 def get_call_argument_by_name(ctx: Union[FunctionContext, MethodContext], name: str) -> Optional[Expression]:
     """
     Return the expression for the specific argument.
-    This helper should only be used with non-star arguments.
     """
-    if name not in ctx.callee_arg_names:
-        return None
-    idx = ctx.callee_arg_names.index(name)
-    args = ctx.args[idx]
-    if len(args) != 1:
-        # Either an error or no value passed.
-        return None
-    return args[0]
+    # first check for named arg on function definition
+    if name in ctx.callee_arg_names:
+        idx = ctx.callee_arg_names.index(name)
+        args = ctx.args[idx]
+        if len(args) != 1:
+            # Either an error or no value passed.
+            return None
+        return args[0]
+
+    # check for named arg in function call keyword args
+    if name in ctx.arg_names[1]:
+        idx = ctx.arg_names[1].index(name)
+        return ctx.args[1][idx]
+
+    return None
 
 
 def get_call_argument_type_by_name(ctx: Union[FunctionContext, MethodContext], name: str) -> Optional[MypyType]:

tests/typecheck/fields/test_custom_fields.yml

@@ -0,0 +1,28 @@
+-   case: test_custom_model_fields_with_passthrough_constructor
+    main: |
+        from myapp.models import User
+        user = User()
+        reveal_type(user.id)  # N: Revealed type is "builtins.int"
+        reveal_type(user.my_custom_field)  # N: Revealed type is "Union[builtins.int, None]"
+    monkeypatch: true
+    installed_apps:
+        - myapp
+    files:
+        -   path: myapp/__init__.py
+        -   path: myapp/models.py
+            content: |
+                from django.db import models
+                from django.db.models import fields
+
+                from typing import Any, TypeVar
+
+                _ST = TypeVar("_ST", contravariant=True)
+                _GT = TypeVar("_GT", covariant=True)
+
+                class MyIntegerField(fields.IntegerField[_ST, _GT]):
+                    def __init__(self, *args: Any, **kwargs: Any) -> None:
+                        super().__init__(*args, **kwargs)
+
+                class User(models.Model):
+                    id = models.AutoField(primary_key=True)
+                    my_custom_field = MyIntegerField(null=True)