branchcache: skip entries that are topological heads in the on disk file
In the majority of cases, topological heads are also branch heads. We have
efficient way to get the topological heads and efficient way to retrieve
their branch information. So there is little value in putting them in the branch
cache file explicitly. On the contrary, writing them explicitly tend to create
very large cache file that are inefficient to read and update.
So the branch cache v3 format is no longer including them. This changeset focus
on the format aspect and have no focus on the performance aspect. We will cover
that later.
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 | grep -E '^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