Cancel message for "Add To Merge Train When Pipeline Succeeds" auto merge strategy is not descriptive enough
The following discussion from !13767 (merged) should be addressed:
I think that this message is not descriptive enough when
cancelhappens due to MWPS unable to enqueue to train.
We should have a better message with better reason, like:
merge is no longer mergable, failed to add to mege train.
Maybe this should be returned by
MergeTrainService#executeresult and be passed to notice send to the system.