Fix TypeAlias with circular reference to class generates NameError (#2591)

* Fix type alias circular reference handling for classes

* Refactor type alias circular reference handling in __update_type_aliases method

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: koxudaxi

src/datamodel_code_generator/parser/base.py

@@ -1454,31 +1454,30 @@ def __set_one_literal_on_default(self, models: list[DataModel]) -> None:
     @classmethod
     def __update_type_aliases(cls, models: list[DataModel]) -> None:
         """Update type aliases to properly handle forward references per PEP 484."""
-        rendered_aliases: set[str] = set()
+        model_index: dict[str, int] = {m.class_name: i for i, m in enumerate(models)}
 
-        for model in models:
+        for i, model in enumerate(models):
             if not isinstance(model, TypeAliasBase):
                 continue
-
             if isinstance(model, TypeStatement):
-                rendered_aliases.add(model.class_name)
                 continue
 
             for field in model.fields:
                 for data_type in field.data_type.all_data_types:
                     if not data_type.reference:
                         continue
                     source = data_type.reference.source
-                    if not isinstance(source, TypeAliasBase):
-                        continue
-                    if isinstance(source, TypeStatement):  # pragma: no cover
+                    if not isinstance(source, DataModel):
+                        continue  # pragma: no cover
+                    if isinstance(source, TypeStatement):
+                        continue  # pragma: no cover
+                    if source.module_path != model.module_path:
                         continue
                     name = data_type.reference.short_name
-                    if name not in rendered_aliases:
+                    source_index = model_index.get(name)
+                    if source_index is not None and source_index >= i:
                         data_type.alias = f'"{name}"'
 
-            rendered_aliases.add(model.class_name)
-
     @classmethod
     def __postprocess_result_modules(cls, results: dict[tuple[str, ...], Result]) -> dict[tuple[str, ...], Result]:
         def process(input_tuple: tuple[str, ...]) -> tuple[str, ...]:

tests/data/expected/main/jsonschema/type_alias_with_circular_ref_to_class_msgspec.py

@@ -0,0 +1,25 @@
+# generated by datamodel-codegen:
+#   filename:  type_alias_with_circular_ref_to_class.json
+#   timestamp: 2019-07-26T00:00:00+00:00
+
+from __future__ import annotations
+
+from typing import List, Union
+
+from msgspec import Struct
+from typing_extensions import TypeAlias
+
+
+class Defaults(Struct):
+    a: List[Span]
+
+
+class SpanB(Struct):
+    recur: List[Span]
+
+
+Either: TypeAlias = Union[SpanB, "Span"]
+
+
+class Span(Struct):
+    recur: List[Either]

tests/data/jsonschema/type_alias_with_circular_ref_to_class.json

@@ -0,0 +1,32 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$defs": {
+    "SpanB": {
+      "type": "object",
+      "properties": {
+        "recur": { "type": "array", "items": [{ "$ref": "#/$defs/Span" }] }
+      },
+      "required": ["recur"]
+    },
+    "Either": { "oneOf": [{ "$ref": "#/$defs/SpanB" }, { "$ref": "#/$defs/Span" }] },
+    "Span": {
+      "type": "object",
+      "properties": {
+        "recur": {
+          "type": "array",
+          "items": [{ "$ref": "#/$defs/Either" }]
+        }
+      },
+      "required": ["recur"]
+    }
+  },
+  "title": "Defaults",
+  "type": "object",
+  "properties": {
+    "a": {
+      "type": "array",
+      "items": [{ "$ref": "#/$defs/Span" }]
+    }
+  },
+  "required": ["a"]
+}

tests/main/jsonschema/test_main_jsonschema.py

@@ -3000,6 +3000,24 @@ def test_main_jsonschema_empty_items_array(output_file: Path) -> None:
     )
 
 
+@MSGSPEC_LEGACY_BLACK_SKIP
+def test_main_jsonschema_type_alias_with_circular_ref_to_class_msgspec(min_version: str, output_file: Path) -> None:
+    """Test TypeAlias with circular reference to class generates quoted forward refs."""
+    run_main_and_assert(
+        input_path=JSON_SCHEMA_DATA_PATH / "type_alias_with_circular_ref_to_class.json",
+        output_path=output_file,
+        input_file_type="jsonschema",
+        assert_func=assert_file_content,
+        expected_file="type_alias_with_circular_ref_to_class_msgspec.py",
+        extra_args=[
+            "--output-model-type",
+            "msgspec.Struct",
+            "--target-python-version",
+            min_version,
+        ],
+    )
+
+
 def test_main_jsonschema_enum_object_values(output_file: Path) -> None:
     """Test that enum with object values uses title/name/const for member names (issue #1620)."""
     run_main_and_assert(