push: rework the computation of fallbackheads to be correct
The previous computation tried to be smart but ended up being wrong. This was
caught by phase movement test while reworking the phase discovery logic to be
faster.
The previous logic was failing to catch case where the pushed set was not based
on a common heads (i.e. when the discovery seemed to have "over discovered"
content, outside the pushed set)
In the following graph, `e` is a common head and we `hg push -r f`. We need to
detect `c` as a fallback heads and we previous failed to do so::
e
|
d f
|/
c
|
b
|
a
The performance impact of the change seems minimal. On the most impacted
repository at hand (mozilla-try), the slowdown seems mostly mixed in the
overall noise `hg push` but seems to be in the hundred of milliseconds order of
magnitude. When using rust, we seems to be a bit faster, probably because we
leverage more accelaratd internals.
I added a couple of performance related common for further investigation later
on.
Checking how hg behaves when one side of a pull/push doesn't support
some capability (because it's running an older hg version, usually).
$ hg init repo1
$ cd repo1
$ echo a > a; hg add -q a; hg commit -q -m a
$ hg bookmark a
$ hg clone -q . ../repo2
$ cd ../repo2
$ touch $TESTTMP/disable-lookup.py
$ disable_cap() {
> rm -f $TESTTMP/disable-lookup.pyc # pyc caching is buggy
> cat <<EOF > $TESTTMP/disable-lookup.py
> from mercurial import extensions, wireprotov1server
> def wcapabilities(orig, *args, **kwargs):
> cap = orig(*args, **kwargs)
> cap.remove(b'$1')
> return cap
> extensions.wrapfunction(wireprotov1server, '_capabilities', wcapabilities)
> EOF
> }
$ cat >> ../repo1/.hg/hgrc <<EOF
> [extensions]
> disable-lookup = $TESTTMP/disable-lookup.py
> EOF
$ hg pull ssh://user@dummy/repo1 -r tip -B a
pulling from ssh://user@dummy/repo1
no changes found
$ disable_cap lookup
$ hg pull ssh://user@dummy/repo1 -r tip -B a
pulling from ssh://user@dummy/repo1
abort: other repository doesn't support revision lookup, so a rev cannot be specified.
[255]
$ disable_cap pushkey
$ hg pull ssh://user@dummy/repo1 -r tip -B a
pulling from ssh://user@dummy/repo1
abort: remote bookmark a not found!
[10]