fix: improve error message for missing operationId

Address review feedback by making the error message more helpful when
operationId and path_name are both missing. The error now includes:
- Operation summary (if present)
- HTTP operation (get, post, etc.)
- Path name value

This helps developers quickly identify which operation in their OpenAPI
spec needs to be fixed.

Also adds test coverage to verify the improved error message includes
all expected details.

Author: Doug Borg

src/openapi_python_generator/language_converters/python/service_generator.py

@@ -248,7 +248,11 @@ def generate_operation_id(
         # Insert underscore before parameter placeholders so /lists/{listId} -> lists_{listId}
         cleaned = re.sub(r"\{([^}]+)\}", r"_\1", path_name)
         return common.normalize_symbol(f"{http_op}_{cleaned}")
-    raise RuntimeError("Missing operationId and path_name for operation")
+    raise RuntimeError(
+        f"Missing operationId and path_name for operation. "
+        f"Details: summary={getattr(operation, 'summary', None)!r}, "
+        f"http_op={http_op!r}, path_name={path_name!r}"
+    )
 
 
 def _generate_params(

tests/test_service_generator.py

@@ -497,3 +497,20 @@ def test_generate_operation_id_path_param_separator():
     op = Operation(responses=default_responses, operationId=None)  # type: ignore[arg-type]
     op_id = generate_operation_id(op, "get", path_name)
     assert op_id == "get_lists_listId"
+
+
+def test_generate_operation_id_error_message_includes_details():
+    """Error message should include operation details to help identify problematic operations."""
+    op = Operation(
+        responses=default_responses, operationId=None, summary="Get user data"  # type: ignore[arg-type]
+    )
+    try:
+        generate_operation_id(op, "get", None)
+        assert False, "Expected RuntimeError to be raised"
+    except RuntimeError as e:
+        error_msg = str(e)
+        # Verify error message includes helpful details
+        assert "Missing operationId and path_name" in error_msg
+        assert "summary='Get user data'" in error_msg
+        assert "http_op='get'" in error_msg
+        assert "path_name=None" in error_msg