grab: gracefully handle the case when we try to grab parent of wdir
Before this patch, we go all the way down to obsmarker creation logic and gets
an error saying that changeset cannot obsolete itself. We should be more smart
here and error out early saying we cannot grab that changeset.
testing topic with shelve extension
------------------------------------
$ . "$TESTDIR/testlib/topic_setup.sh"
$ hg init repo
$ cd repo
$ cat <<EOF >>.hg/hgrc
> [extensions]
> shelve=
> EOF
$ touch a
$ echo "Hello" >> a
$ hg topic "testing-shelve"
marked working directory as topic: testing-shelve
$ hg topic
* testing-shelve (0 changesets)
$ hg ci -m "First commit" -A
adding a
active topic 'testing-shelve' grew its first changeset
$ hg topic
* testing-shelve (1 changesets)
$ echo " World" >> a
$ hg stack
### topic: testing-shelve
### target: default (branch)
t1@ First commit (current)
shelve test
-----------
$ hg shelve
shelved as default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg topic
* testing-shelve (1 changesets)
$ hg stack
### topic: testing-shelve
### target: default (branch)
t1@ First commit (current)
unshelve test
-------------
$ hg unshelve
unshelving change 'default'
$ hg topic
* testing-shelve (1 changesets)
$ hg stack
### topic: testing-shelve
### target: default (branch)
t1@ First commit (current)