Fix GraphQL enum renaming issue (#2642)

* add tests

* use reference instead of type on enums

* change test example

Author: siminn-arnorgj

src/datamodel_code_generator/parser/graphql.py

@@ -482,7 +482,8 @@ def parse_field(
             data_type.reference = self.references[obj.name]
 
         obj = graphql.assert_named_type(obj)
-        data_type.type = obj.name
+        if data_type.reference is None:
+            data_type.type = obj.name
 
         required = (not self.force_optional_for_required_fields) and (not final_data_type.is_optional)
 

tests/data/expected/main/graphql/enum_casing.py

@@ -0,0 +1,31 @@
+# generated by datamodel-codegen:
+#   filename:  enum-casing.graphql
+#   timestamp: 2019-07-26T00:00:00+00:00
+
+from __future__ import annotations
+
+from enum import Enum
+from typing import Literal, Optional
+
+from pydantic import BaseModel, Field
+from typing_extensions import TypeAlias
+
+Boolean: TypeAlias = bool
+"""
+The `Boolean` scalar type represents `true` or `false`.
+"""
+
+
+String: TypeAlias = str
+"""
+The `String` scalar type represents textual data, represented as UTF-8 character sequences. The String type is most often used by GraphQL to represent free-form human-readable text.
+"""
+
+
+class Lowercase(Enum):
+    foo = 'foo'
+
+
+class EnumRef(BaseModel):
+    bar: Lowercase
+    typename__: Optional[Literal['EnumRef']] = Field('EnumRef', alias='__typename')

tests/data/graphql/enum-casing.graphql

@@ -0,0 +1,7 @@
+enum lowercase {
+  foo
+}
+
+type EnumRef {
+  bar: lowercase!
+}

tests/main/graphql/test_main_graphql.py

@@ -102,6 +102,21 @@ def test_main_graphql_field_aliases(output_file: Path) -> None:
     )
 
 
+@pytest.mark.skipif(
+    black.__version__.split(".")[0] == "19",
+    reason="Installed black doesn't support the old style",
+)
+def test_main_graphql_enum_casing(output_file: Path) -> None:
+    """Test GraphQL code generation with enums."""
+    run_main_and_assert(
+        input_path=GRAPHQL_DATA_PATH / "enum-casing.graphql",
+        output_path=output_file,
+        input_file_type="graphql",
+        assert_func=assert_file_content,
+        expected_file="enum_casing.py",
+    )
+
+
 @pytest.mark.skipif(
     black.__version__.split(".")[0] == "19",
     reason="Installed black doesn't support the old style",