Add support for x-enumNames extension (#2653)

* Add x-enumNames support for OpenAPI schemas and update related parsing logic

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

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---------

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

Author: koxudaxi

src/datamodel_code_generator/parser/jsonschema.py

@@ -333,7 +333,8 @@ def validate_null_type(cls, value: Any) -> Any:  # noqa: N805
     required: list[str] = []  # noqa: RUF012
     ref: Optional[str] = Field(default=None, alias="$ref")  # noqa: UP045
     nullable: Optional[bool] = False  # noqa: UP045
-    x_enum_varnames: list[str] = Field(default=[], alias="x-enum-varnames")
+    x_enum_varnames: list[str] = Field(default_factory=list, alias="x-enum-varnames")
+    x_enum_names: list[str] = Field(default_factory=list, alias="x-enumNames")
     description: Optional[str] = None  # noqa: UP045
     title: Optional[str] = None  # noqa: UP045
     example: Any = None
@@ -2390,14 +2391,16 @@ def parse_enum(
 
         exclude_field_names: set[str] = set()
 
+        enum_names = obj.x_enum_varnames or obj.x_enum_names
+
         for i, enum_part in enumerate(enum_times):
             if obj.type == "string" or isinstance(enum_part, str):
                 default = f"'{enum_part.translate(escape_characters)}'" if isinstance(enum_part, str) else enum_part
-                field_name = obj.x_enum_varnames[i] if obj.x_enum_varnames else str(enum_part)
+                field_name = enum_names[i] if enum_names and i < len(enum_names) and enum_names[i] else str(enum_part)
             else:
                 default = enum_part
-                if obj.x_enum_varnames:
-                    field_name = obj.x_enum_varnames[i]
+                if enum_names and i < len(enum_names) and enum_names[i]:
+                    field_name = enum_names[i]
                 elif isinstance(enum_part, dict):
                     field_name = self._get_field_name_from_dict_enum(enum_part, i)
                 else:

tests/data/expected/main/openapi/x_enum_names.py

@@ -0,0 +1,33 @@
+# generated by datamodel-codegen:
+#   filename:  x_enum_names.yaml
+#   timestamp: 2019-07-26T00:00:00+00:00
+
+from __future__ import annotations
+
+from enum import Enum, IntEnum
+
+
+class CustomerColor(IntEnum):
+    BloodOrange = 1
+    Sunflower = 2
+    LightGreen = 3
+    SkyBlue = 4
+    Purple = 5
+
+
+class StringStatus(Enum):
+    Pending = 'pending'
+    Active = 'active'
+    Closed = 'closed'
+
+
+class PriorityTest(IntEnum):
+    VarnameOne = 1
+    VarnameTwo = 2
+
+
+class ShortNames(IntEnum):
+    First = 1
+    Second = 2
+    integer_3 = 3
+    integer_4 = 4

tests/data/openapi/x_enum_names.yaml

@@ -0,0 +1,45 @@
+openapi: 3.0.0
+info:
+  title: Test x-enumNames
+  version: 1.0.0
+paths: {}
+components:
+  schemas:
+    # Integer enum with x-enumNames
+    CustomerColor:
+      type: integer
+      enum: [1, 2, 3, 4, 5]
+      x-enumNames:
+        - BloodOrange
+        - Sunflower
+        - LightGreen
+        - SkyBlue
+        - Purple
+
+    # String enum with x-enumNames
+    StringStatus:
+      type: string
+      enum: ['pending', 'active', 'closed']
+      x-enumNames:
+        - Pending
+        - Active
+        - Closed
+
+    # x-enum-varnames takes priority over x-enumNames
+    PriorityTest:
+      type: integer
+      enum: [1, 2]
+      x-enum-varnames:
+        - VarnameOne
+        - VarnameTwo
+      x-enumNames:
+        - EnumNameOne
+        - EnumNameTwo
+
+    # x-enumNames shorter than enum (graceful fallback)
+    ShortNames:
+      type: integer
+      enum: [1, 2, 3, 4]
+      x-enumNames:
+        - First
+        - Second

tests/main/openapi/test_main_openapi.py

@@ -3463,3 +3463,14 @@ def test_main_nested_package_enum_default(output_dir: Path) -> None:
                 "--set-default-enum-member",
             ],
         )
+
+
+def test_main_openapi_x_enum_names(output_file: Path) -> None:
+    """Test OpenAPI generation with x-enumNames extension (NSwag/NJsonSchema style)."""
+    run_main_and_assert(
+        input_path=OPEN_API_DATA_PATH / "x_enum_names.yaml",
+        output_path=output_file,
+        input_file_type="openapi",
+        assert_func=assert_file_content,
+        expected_file="x_enum_names.py",
+    )