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.
$ cat <<EOF > merge
> import sys, os
> print("merging for", os.path.basename(sys.argv[1]))
> EOF
$ HGMERGE="$PYTHON ../merge"; export HGMERGE
$ hg init A1
$ cd A1
$ echo This is file foo1 > foo
$ echo This is file bar1 > bar
$ hg add foo bar
$ hg commit -m "commit text"
$ cd ..
$ hg clone A1 B1
updating to branch default
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd A1
$ rm bar
$ hg remove bar
$ hg commit -m "commit test"
$ cd ../B1
$ echo This is file foo22 > foo
$ hg commit -m "commit test"
$ cd ..
$ hg clone A1 A2
updating to branch default
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg clone B1 B2
updating to branch default
2 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ cd A1
$ hg pull ../B1
pulling from ../B1
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files (+1 heads)
new changesets b90e70beeb58
1 local changesets published
(run 'hg heads' to see heads, 'hg merge' to merge)
$ hg merge
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg commit -m "commit test"
bar should remain deleted.
$ hg manifest --debug
f9b0e817f6a48de3564c6b2957687c5e7297c5a0 644 foo
$ cd ../B2
$ hg pull ../A2
pulling from ../A2
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 0 changes to 0 files (+1 heads)
new changesets e1adc944e717
(run 'hg heads' to see heads, 'hg merge' to merge)
$ hg merge
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
(branch merge, don't forget to commit)
$ hg commit -m "commit test"
bar should remain deleted.
$ hg manifest --debug
f9b0e817f6a48de3564c6b2957687c5e7297c5a0 644 foo
$ cd ..