transaction: quietly rollback if no other changes than temporary files
If no actual change have been made, we don't really need to roll them back. We
only have to cleanup some temporary files and it seems reasonable to do that
quietly.
This will help us to use the transaction in wider context¹ without impacting the
user experience.
[1] as in Python context managers that lives longer.
Tests about metadataonlyctx
$ hg init
$ echo A > A
$ hg commit -A A -m 'Add A'
$ echo B > B
$ hg commit -A B -m 'Add B'
$ hg rm A
$ echo C > C
$ echo B2 > B
$ hg add C -q
$ hg commit -m 'Remove A'
$ cat > metaedit.py <<EOF
> from mercurial import context, pycompat, registrar
> cmdtable = {}
> command = registrar.command(cmdtable)
> @command(b'metaedit')
> def metaedit(ui, repo, arg):
> # Modify commit message to "FOO"
> with repo.wlock(), repo.lock(), repo.transaction(b'metaedit'):
> old = repo[b'.']
> kwargs = dict(s.split(b'=', 1) for s in arg.split(b';'))
> if b'parents' in kwargs:
> kwargs[b'parents'] = map(int, kwargs[b'parents'].split(b','))
> new = context.metadataonlyctx(repo, old,
> **pycompat.strkwargs(kwargs))
> new.commit()
> EOF
$ hg --config extensions.metaedit=$TESTTMP/metaedit.py metaedit 'text=Changed'
$ hg log -r tip
changeset: 3:ad83e9e00ec9
tag: tip
parent: 1:3afb7afe6632
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: Changed
$ hg --config extensions.metaedit=$TESTTMP/metaedit.py metaedit 'parents=0' 2>&1 | egrep '^RuntimeError'
RuntimeError: can't reuse the manifest: its p1 doesn't match the new ctx p1
$ hg --config extensions.metaedit=$TESTTMP/metaedit.py metaedit 'user=foo <foo@example.com>'
$ hg log -r tip
changeset: 4:1f86eaeca92b
tag: tip
parent: 1:3afb7afe6632
user: foo <foo@example.com>
date: Thu Jan 01 00:00:00 1970 +0000
summary: Remove A