Handling changed/deleted conflicts with non-interactive terminals

[Angel Ezquerra]

On Tue, Oct 1, 2013 at 5:57 AM, Siddharth Agarwal <sid0 at fb.com> wrote:
> One issue that's popped up here recently is handling changed/deleted
> conflicts (cdcs for short) during merges, when the terminal is
> non-interactive. cdcs occur when the file to be merged is changed on one
> side and deleted on the other.
>
> Currently (in merge.py:manifestmerge) we always choose the default option,
> which is to keep the changed file. That's reasonably sensible, but there's
> no way for the process that's using hg non-interactively to figure that out,
> short of grepping for the string in hg's output. There's also no indication
> that something's gone wrong, nor a non-zero exit code.
>
> Our use case is an automatic rebase-and-push done on a server -- it needs to
> fail and go back and ask the user to manually rebase in the c/d case. We've
> currently worked around it by grepping output, but it would be great to have
> a non-hacky solution for this.
>
> mpm and I worked out a tentative solution today, which goes something like:
> - for non-interactive terminals, treat cdcs as unresolved
> - add a new status to the persistent merge state, for cdcs
> - hg resolve <cdc path> shows the current prompt: either local changed
> remote deleted or local deleted remote changed.
> - hg resolve --mark <cdc path> keeps the changed version
> - hg rm <cdc path> && hg resolve --mark <cdc path> deletes the file
>
> For backwards compatibility, we'll need to store the extra statuses in a
> separate file so that older hg won't barf at it. Figuring out when and how
> to invalidate that file is somewhat tricky.
>
> Does the general idea make sense? Is there anything we're missing here that
> should be added?
>
> mpm mentioned that this would be useful to TortoiseHg as well, so ccing
> Steve Borho.

I think this good be nice, and as you say it would be useful to TortoiseHg.

Perhaps it would also make sense to do this for other sorts of merge
prompts, such as subrepo path change conflict prompts (and the
recently introduced subrepo merge/local/other selection prompts)?

Cheers,

Angel