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).
Check that evolve shows error while handling split commits
--------------------------------------
$ cat >> $HGRCPATH <<EOF
> [defaults]
> amend=-d "0 0"
> fold=-d "0 0"
> [web]
> push_ssl = false
> allow_push = *
> [phases]
> publish = False
> [diff]
> git = 1
> unified = 0
> [ui]
> logtemplate = {rev}:{node|short}@{branch}({phase}) {desc|firstline}\n
> [extensions]
> EOF
$ echo "evolve=$(echo $(dirname $TESTDIR))/hgext3rd/evolve/" >> $HGRCPATH
$ mkcommit() {
> echo "$1" > "$1"
> hg add "$1"
> hg ci -m "add $1"
> }
$ hg init split
$ cd split
$ mkcommit aa
Create a split commit
$ printf "oo" > oo;
$ printf "pp" > pp;
$ hg add oo pp
$ hg commit -m "oo+pp"
$ mkcommit uu
$ hg up 0
0 files updated, 0 files merged, 3 files removed, 0 files unresolved
$ printf "oo" > oo;
$ hg add oo
$ hg commit -m "_oo"
created new head
$ printf "pp" > pp;
$ hg add pp
$ hg commit -m "_pp"
$ hg prune --successor "desc(_oo) + desc(_pp)" -r "desc('oo+pp')" --split
1 changesets pruned
1 new orphan changesets
$ hg log -G
@ 4:d0dcf24cddd3@default(draft) _pp
|
o 3:a7fdfda64c08@default(draft) _oo
|
| * 2:f52200b086ca@default(draft) add uu
| |
| x 1:d55647aaa0c6@default(draft) oo+pp
|/
o 0:58663bb03074@default(draft) add aa
$ hg evolve --rev "0::"
move:[2] add uu
atop:[4] _pp