rhg: desambiguate status without decompressing filelog if possible
When status is unsure based on `stat()` and the dirstate if a file is clean
or modified, we need to compare it against the filelog.
This comparison can skip looking at contents if the lengths differ.
This changeset optimize this further to deduce what we can about the length
if the filelog without decompressing it or resolving deltas.
Differential Revision: https://phab.mercurial-scm.org/D11965
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 __future__ import absolute_import
> 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