feat(variant): add reason when variant generation fails

antarest/study/storage/variantstudy/variant_study_service.py

@@ -42,7 +42,7 @@
 from antarest.core.filetransfer.model import FileDownloadTaskDTO
 from antarest.core.interfaces.cache import ICache
 from antarest.core.interfaces.eventbus import Event, EventChannelDirectory, EventType, IEventBus
-from antarest.core.jwt import DEFAULT_ADMIN_USER, JWTUser
+from antarest.core.jwt import DEFAULT_ADMIN_USER
 from antarest.core.model import JSON, PermissionInfo, PublicMode, StudyPermissionType
 from antarest.core.requests import RequestParameters, UserHasNotPermissionError
 from antarest.core.serialization import to_json_string
@@ -971,20 +971,28 @@ def _safe_generation(self, metadata: VariantStudy, timeout: int = DEFAULT_AWAIT_
             task_id = self.generate_task(metadata)
             self.task_service.await_task(task_id, timeout)
             result = self.task_service.status_task(task_id, RequestParameters(DEFAULT_ADMIN_USER))
-            if result.result and result.result.success:
+            if not result.result:
+                raise ValueError("No task result")
+            if result.result.success:
                 # OK, the study has been generated
                 return
-            raise ValueError("No task result or result failed")
+            # The variant generation failed, we have to raise a clear exception.
+            error_msg = result.result.message
+            stripped_msg = error_msg.removeprefix(
+                f"Task {task_id} failed: Unhandled exception 417: Failed to generate variant study {metadata.id}"
+            )
+            final_msg = stripped_msg.splitlines()[0]
+            raise ValueError(final_msg)
 
         except concurrent.futures.TimeoutError as e:
             # Raise a REQUEST_TIMEOUT error (408)
             logger.error(f"⚡ Timeout while generating variant study {metadata.id}", exc_info=e)
-            raise VariantGenerationTimeoutError(f"Timeout while generating {metadata.id}") from None
+            raise VariantGenerationTimeoutError(f"Timeout while generating variant {metadata.id}") from None
 
         except Exception as e:
             # raise a EXPECTATION_FAILED error (417)
             logger.error(f"⚡ Fail to generate variant study {metadata.id}", exc_info=e)
-            raise VariantGenerationError(f"Error while generating {metadata.id}") from None
+            raise VariantGenerationError(f"Error while generating variant {metadata.id} {e.args[0]}") from None
 
     @staticmethod
     def _get_snapshot_last_executed_command_index(

tests/storage/business/test_variant_study_service.py

@@ -56,9 +56,6 @@ def test_get(tmp_path: str, project_path) -> None:
     data = {"titi": 43}
     sub_route = "settings"
 
-    path = path_study / "settings"
-    key = "titi"
-
     study = Mock()
     study.get.return_value = data
     study_factory = Mock()
@@ -104,7 +101,7 @@ def task_status(*args):
             yield t
 
     study_service.task_service.status_task.side_effect = task_status()
-    with pytest.raises(VariantGenerationError, match="Error while generating study2.py"):
+    with pytest.raises(VariantGenerationError, match="Error while generating variant study2.py"):
         study_service.get(metadata=metadata, url=sub_route, depth=2)
     study_service.task_service.await_task.assert_called()