cmdstate: introduce a "saver" contextmanager and use it in place of save()
Previously, the state was only saved in some paths out of these functions. This
can be problematic, if the user ctrl-c's (or `kill -9`'s) the process, or we
exit out of `relocate` for anything besides the "expected" reason, we won't
record that we were in the middle of an evolve.
One of our users has discovered that this leaves hg in a weird state; the user
did something like this:
```
$ hg evolve
<something goes wrong with the merge tool, hits ctrl-c>
<deals with the merge conflicts>
$ hg evolve --continue
abort: no interrupted evolve to continue
$ hg evolve
abort: uncommitted changes
# Note: commands.status.verbose=True is set.
$ hg status
M foo
# The repository is in an unfinished *update* state.
# No unresolved merge conflicts
# To continue: hg update
```
The user did an `hg update`, but it didn't actually do anything besides take it
out of the unfinished update state (the files were still dirty in the working
directory).
Test for issue 5881 present at https://bz.mercurial-scm.org/show_bug.cgi?id=5881
===============================================================================
which is about that if the working copy parent is obsolete then evolve update
to its successor revision and stop; it doesn't continue to evolve remaining
revisions those were suppossed to evovle.
Setup
=====
$ cat >> $HGRCPATH <<EOF
> [phases]
> publish = False
> [alias]
> glog = log -GT "{rev}:{node|short} {desc}\n ({bookmarks}) {phase}"
> [extensions]
> EOF
$ echo "evolve=$(echo $(dirname $TESTDIR))/hgext3rd/evolve/" >> $HGRCPATH
$ hg init issue5881
$ cd issue5881
Prepare the directory by creating an orphan and update to its obsolete parent:
$ for ch in a b c; do echo $ch > $ch; hg ci -Am "added "$ch; done;
adding a
adding b
adding c
$ hg up 1 -q
$ hg ci --amend -m "updated b"
1 new orphan changesets
$ hg up 1
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
working directory parent is obsolete! (5f6d8a4bf34a)
(use 'hg evolve' to update to its successor: e6048a693c0d)
$ hg glog
o 3:e6048a693c0d updated b
| () draft
| * 2:155349b645be added c
| | () draft
| @ 1:5f6d8a4bf34a added b
|/ () draft
o 0:9092f1db7931 added a
() draft
Test `hg evolve` evolve all the revisions specified by user:
$ hg evolve -r .::
update:[3] updated b
0 files updated, 0 files merged, 0 files removed, 0 files unresolved
working directory is now at e6048a693c0d
move:[2] added c
atop:[3] updated b
working directory is now at e6048a693c0d