Merge proposal diffs don't highlight conflicts

[Tim Kuhlman]

I updated a mp with new code at https://code.launchpad.net/~canonical-sysadmins/canonical-is-firewalls/+git/fwgen/+merge/299365 on 7/11/2016 and the master branch had additional commits between the time of the original mp and the new code. The MP tried to merge and failed and instead of indicating a manual merge was needed just placed ====/>>>>> lines in the mp itself. A better approach would just be to refuse to show a diff and instead show a message that would clue me into the need for a rebase.

[Colin Watson (cjwatson)]

This isn't Git-specific; Launchpad has always behaved this way for Bazaar-based MPs too.

I don't think we should entirely refuse to show a diff, since it can often be useful for a reviewer to see it even before the proposer has dealt with resolving conflicts, but perhaps it should be more obvious that there are conflicts. I believe that we do show a conflict indication quite near the top of the page already though.

[Tom Haddon (mthaddon)]

I'm pretty sure there's a line that says something like "Text conflicts" in the summary section at the top under "Diff against target" (I did see this on the MP in question). I agree it could be made more prominent though.