rebase: improve error message for empty --source set
Before, it just said 'nothing to rebase' in this case. Now, it aborts
mentioning the reason: 'empty "source" revision set'.
Specifying revisions that cannot be rebased is a 'soft' error, but specifying
an empty set deserves an abort that explains exactly what the problem is.
$ cat >> $HGRCPATH <<EOF
> [extensions]
> rebase=
>
> [alias]
> tglog = log -G --template "{rev}: '{desc}' {branches}\n"
> EOF
$ hg init repo
$ cd repo
$ echo A > a
$ echo >> a
$ hg ci -Am A
adding a
$ echo B > a
$ echo >> a
$ hg ci -m B
$ echo C > a
$ echo >> a
$ hg ci -m C
$ hg up -q -C 0
$ echo D >> a
$ hg ci -Am AD
created new head
$ hg tglog
@ 3: 'AD'
|
| o 2: 'C'
| |
| o 1: 'B'
|/
o 0: 'A'
$ hg rebase -s 1 -d 3
merging a
merging a
saved backup bundle to $TESTTMP/repo/.hg/strip-backup/*-backup.hg (glob)
$ hg tglog
o 3: 'C'
|
o 2: 'B'
|
@ 1: 'AD'
|
o 0: 'A'
$ cd ..