Guard OpenAPI path items (#3397)

* Guard OpenAPI path items

* Use fixtures for OpenAPI path item guard test

* Avoid infer type fixture scan

Author: koxudaxi

src/datamodel_code_generator/parser/openapi.py

@@ -633,15 +633,19 @@ def _process_path_items(  # noqa: PLR0913
                 for operation_name, raw_operation in methods.items():
                     if operation_name not in OPERATION_NAMES:
                         continue
+                    operation = raw_operation
                     if item_parameters:
+                        operation = operation.copy()
                         if "parameters" in raw_operation:
-                            raw_operation["parameters"].extend(item_parameters)
+                            operation["parameters"] = [*raw_operation["parameters"], *item_parameters]
                         else:
-                            raw_operation["parameters"] = item_parameters.copy()
-                    if security is not None and "security" not in raw_operation:
+                            operation["parameters"] = item_parameters.copy()
+                    if security is not None and "security" not in operation:
                         # fastapi-code-generator depends on inherited global security being materialized here.
-                        raw_operation["security"] = security
-                    self.parse_operation(raw_operation, [*path, operation_name])
+                        if operation is raw_operation:
+                            operation = operation.copy()
+                        operation["security"] = security
+                    self.parse_operation(operation, [*path, operation_name])
 
     def parse_schema(
         self,

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

@@ -0,0 +1,10 @@
+# generated by datamodel-codegen:
+#   filename:  openapi.yaml
+
+from __future__ import annotations
+
+from pydantic import BaseModel
+
+
+class Item(BaseModel):
+    name: str | None = None

tests/data/openapi/referenced_path_item_mutation_guard/openapi.yaml

@@ -0,0 +1,21 @@
+openapi: 3.1.0
+info:
+  title: Path Item Mutation Guard
+  version: 1.0.0
+security:
+  - api_key: []
+paths:
+  /cached:
+    $ref: ./path-item.yml#/paths/~1items
+components:
+  schemas:
+    Item:
+      type: object
+      properties:
+        name:
+          type: string
+  securitySchemes:
+    api_key:
+      type: apiKey
+      in: header
+      name: X-API-Key

tests/data/openapi/referenced_path_item_mutation_guard/path-item.yml

@@ -0,0 +1,20 @@
+paths:
+  /items:
+    parameters:
+      - name: pathLevel
+        in: query
+        schema:
+          type: string
+    get:
+      parameters:
+        - name: operationLevel
+          in: query
+          schema:
+            type: integer
+      responses:
+        '200':
+          description: Success
+          content:
+            application/json:
+              schema:
+                $ref: ./openapi.yaml#/components/schemas/Item

tests/main/openapi/test_main_openapi.py

@@ -26,6 +26,7 @@
     generate,
     get_version,
     inferred_message,
+    load_data_from_path,
 )
 from datamodel_code_generator.__main__ import Exit
 from datamodel_code_generator.config import GenerateConfig
@@ -49,6 +50,7 @@
     MSGSPEC_LEGACY_BLACK_SKIP,
     OPEN_API_DATA_PATH,
     TIMESTAMP,
+    run_generate_file_and_assert,
     run_main_and_assert,
     run_main_url_and_assert,
     run_main_with_args,
@@ -4218,6 +4220,24 @@ def test_main_openapi_non_operations_and_security(output_file: Path) -> None:
     )
 
 
+def test_generate_openapi_keeps_referenced_path_item_original_unchanged(output_file: Path) -> None:
+    """Keep cached referenced OpenAPI path items unchanged while inheriting operation metadata."""
+    input_path = OPEN_API_DATA_PATH / "referenced_path_item_mutation_guard" / "openapi.yaml"
+    path_item_path = OPEN_API_DATA_PATH / "referenced_path_item_mutation_guard" / "path-item.yml"
+    cached_path_item = load_data_from_path(path_item_path.resolve(), "utf-8")
+
+    run_generate_file_and_assert(
+        input_path=input_path,
+        output_path=output_file,
+        input_file_type=InputFileType.OpenAPI,
+        assert_func=assert_file_content,
+        expected_file="referenced_path_item_mutation_guard.py",
+        disable_timestamp=True,
+        openapi_scopes=[OpenAPIScope.Schemas, OpenAPIScope.Paths],
+        unchanged_inputs={"cached path-item.yml": cached_path_item},
+    )
+
+
 def test_main_openapi_webhooks_with_parameters(output_file: Path) -> None:
     """Test OpenAPI generation with webhook-level and operation-level parameters."""
     run_main_and_assert(