add support for _meta.get_field() typechecking

mypy_django_plugin/transformers/meta.py

@@ -0,0 +1,38 @@
+from django.core.exceptions import FieldDoesNotExist
+from mypy.plugin import MethodContext
+from mypy.types import AnyType, Type as MypyType, TypeOfAny, Instance
+
+from mypy_django_plugin.django.context import DjangoContext
+from mypy_django_plugin.lib import fullnames, helpers
+
+
+def _get_field_instance(ctx: MethodContext, field_fullname: str) -> MypyType:
+    field_info = helpers.lookup_fully_qualified_typeinfo(ctx.api, field_fullname)
+    return Instance(field_info, [AnyType(TypeOfAny.explicit), AnyType(TypeOfAny.explicit)])
+
+
+def return_proper_field_type_from_get_field(ctx: MethodContext, django_context: DjangoContext) -> MypyType:
+    model_type = ctx.type.args[0]
+    if not isinstance(model_type, Instance):
+        return _get_field_instance(ctx, fullnames.FIELD_FULLNAME)
+
+    model_cls = django_context.get_model_class_by_fullname(model_type.type.fullname())
+    if model_cls is None:
+        return _get_field_instance(ctx, fullnames.FIELD_FULLNAME)
+
+    field_name_expr = helpers.get_call_argument_by_name(ctx, 'field_name')
+    if field_name_expr is None:
+        return _get_field_instance(ctx, fullnames.FIELD_FULLNAME)
+
+    field_name = helpers.resolve_string_attribute_value(field_name_expr, ctx, django_context)
+    if field_name is None:
+        return _get_field_instance(ctx, fullnames.FIELD_FULLNAME)
+
+    try:
+        field = model_cls._meta.get_field(field_name)
+    except FieldDoesNotExist as exc:
+        ctx.api.fail(exc.args[0], ctx.context)
+        return AnyType(TypeOfAny.from_error)
+
+    field_fullname = helpers.get_class_fullname(field.__class__)
+    return _get_field_instance(ctx, field_fullname)