update: use context manager for config override (API)
Note that update wasn't resetting the value before, so any extensions
that called commands.update() and relied on ui.forcemerge being set
after it returned would now have to set it themselves.
(There technically a small API change in all of the patches in this
series, I believe: If extensions relied on the methods to *clear*
ui.forcemerge, then they would have to do that themselves now, because
ui.configoverride() actually restores the previous config, it doesn't
just clear it like these functions did before.)
Differential Revision: https://phab.mercurial-scm.org/D3741
https://bz.mercurial-scm.org/619
$ hg init
$ echo a > a
$ hg ci -Ama
adding a
$ echo b > b
$ hg branch b
marked working directory as branch b
(branches are permanent and global, did you want a bookmark?)
$ hg ci -Amb
adding b
$ hg co -C 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
Fast-forward:
$ hg merge b
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg ci -Ammerge
Bogus fast-forward should fail:
$ hg merge b
abort: merging with a working directory ancestor has no effect
[255]
Even with strange revset (issue4465)
$ hg merge ::.
abort: merging with a working directory ancestor has no effect
[255]