scmutil: add function to help handling workingctx in arithmetic operation
It's unfortunate that workingctx revision is None, which doesn't work well in
arithmetic operation or comparison. This function is trivial but will be used
in several places.
$ hg init
$ echo This is file a1 > a
$ echo This is file b1 > b
$ hg add a b
$ hg commit -m "commit #0"
$ echo This is file b22 > b
$ hg commit -m "comment #1"
$ hg update 0
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ rm b
$ hg commit -A -m "comment #2"
removing b
created new head
$ hg update 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg update
abort: not a linear update
(merge or update --check to force update)
[255]
$ rm b
$ hg update -c
abort: uncommitted changes
[255]
$ hg revert b
$ hg update -c
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ mv a c
Should abort:
$ hg update 1
abort: uncommitted changes
(commit or update --clean to discard changes)
[255]
$ mv c a
Should succeed:
$ hg update 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved