Consider how to handle failed cherry-picks

[Mariatta]

From @ncoghlan on March 12, 2017 4:57

I think this utility has a lot of potential to evolve into the bot that actually does the automated cherry-pick PR creation, and one of the things we'll need to address there is what to do when the routine cherry pick fails.

At the moment, if the first cherry-pick fails, it leaves the checkout in a messy state, so all the subsequent branch creation commands fail.

I'm thinking one way of tackling this would be to:

Complain and exit early if the checkout is in a messy state, and suggesting running git stash to move the local changes aside.
If any of the cherry-picks fail do an immediate git reset --hard and move on to the next branch.
Does that approach sound reasonable?

Copied from original issue: Mariatta/chic_a_cherry_picker#15

[ncoghlan]

#51 points out that for the interactive use case, it's likely to be helpful to drop the user into the failed cherry-pick directory with a printed command on:

• how to finish the current cherry-pick
• how to resume any other not-yet-attempted cherry-picks

[serhiy-storchaka]

Would be nice if cherry_picker.py be allowing to fix errors manually and continue its work when run with --continue. Running with --abort should abort the current conflict resolution process, reset the workspace and delete just created branch.

[Mariatta]

Thanks @serhiy-storchaka . I started working on handling errors in cherry_picker.py see #57
I implemented the interactive mode where it will ask the user of how to proceed.
But if we want it as --continue or --abort options, it can be done.

[ncoghlan]

The --continue/--abort approach would align nicely with the way git's own commands work, so +1 from me for that approach.

[Mariatta]

Please check if #65 does what's expected. Thanks :)