relnotes: add note about changed labels texts Differential Revision: https://phab.mercurial-scm.org/D12085

graft: attempt to make merge labels more helpful Differential Revision: https://phab.mercurial-scm.org/D12025

shelve: attempt to make merge labels more helpful Differential Revision: https://phab.mercurial-scm.org/D12024

histedit: attempt to make merge labels more helpful Differential Revision: https://phab.mercurial-scm.org/D12023

update: set custom conflict label for base commit Differential Revision: https://phab.mercurial-scm.org/D12022

merge: set custom conflict label for base commit Differential Revision: https://phab.mercurial-scm.org/D12021

rebase: set custom conflict label for base commit Differential Revision: https://phab.mercurial-scm.org/D12020

simplemerge: take over formatting of label from `filemerge` The padding we do of conflict labels depends on which conflict marker style is used. For two-way conflict markers (the default), the length of the base label shouldn't matter. It does before this patch, however. This patch moves the formatting from `filemerge` to `simplemerge`. The latter knows which conflict marker style to use, so it can easily decide about the padding. This change will allow us to use more descriptive "base" labels without causing illogical padding in 2-way markers. I'll do that next. One wrinkle is that we pass the same labels to external merge tools. I decided to change that in this patch to be simpler: no padding, and no ellipsis to fit within 80 columns. My reasoning is that the typical external, 3-or-4-panel merge tool doesn't show the labels on top of each others, so the padding doesn't make sense there. The ellipsis is probably not necessary because the external tools probably have their own way of dealing with long labels. Also, we limit them to "80 - 8" to fit the "<<<<<<< " before, which is almost definitely not what an external tool would put there. Differential Revision: https://phab.mercurial-scm.org/D12019

filemerge: pass `simplemerge.MergeInput` to tool functions Differential Revision: https://phab.mercurial-scm.org/D12018

filemerge: work with `simplemerge.MergeInput` in `filemerge()` We currently pass around pairs of file context objects and labels between functions in the `filemerge` module. I plan to pass around `simplemerge.MergeInput` instead. This patch prepares for that by using the type internally in `filemerge.filemerge()`. Differential Revision: https://phab.mercurial-scm.org/D12017

filemerge: always define a "base" label It simplifies the code and improves the conflict markers to always have the "base" label defined. Differential Revision: https://phab.mercurial-scm.org/D12016

filemerge: set default labels a little earlier By setting the default labels a little earlier, we can rely on them always being set, as far as I can tell. It may actually even be fine to rely on that even if we don't set them earlier, but it makes more sense to me to do it. Differential Revision: https://phab.mercurial-scm.org/D12015

helptext: add missing newline to Rust helptext This makes it so the list renders properly. Differential Revision: https://phab.mercurial-scm.org/D12007

unamend: error out when running on merge commit It's better to error out than to produce a bad commit. We do that same in `hg uncommit`. I haven't looked into how much work it is to make them work instead. Differential Revision: https://phab.mercurial-scm.org/D12087

tests: demonstrate how `hg unamend` fails on merge commits When `hg unamend` is run on a merge commit, it seems that it loses the changes from the second parent. Differential Revision: https://phab.mercurial-scm.org/D12086