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.
$ hg init repo
$ cd repo
$ echo line 1 > foo
$ hg ci -qAm 'add foo'
copy foo to bar and change both files
$ hg cp foo bar
$ echo line 2-1 >> foo
$ echo line 2-2 >> bar
$ hg ci -m 'cp foo bar; change both'
in another branch, change foo in a way that doesn't conflict with
the other changes
$ hg up -qC 0
$ echo line 0 > foo
$ hg cat foo >> foo
$ hg ci -m 'change foo'
created new head
we get conflicts that shouldn't be there
$ hg merge -P
changeset: 1:484bf6903104
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: cp foo bar; change both
$ hg merge --debug
unmatched files in other:
bar
all copies found (* = to merge, ! = divergent, % = renamed and deleted):
on remote side:
src: 'foo' -> dst: 'bar' *
checking for directory renames
resolving manifests
branchmerge: True, force: False, partial: False
ancestor: e6dc8efe11cc, local: 6a0df1dad128+, remote: 484bf6903104
starting 4 threads for background file closing (?)
preserving foo for resolve of bar
preserving foo for resolve of foo
bar: remote copied from foo -> m
picked tool ':merge' for bar (binary False symlink False changedelete False)
merging foo and bar to bar
my bar@6a0df1dad128+ other bar@484bf6903104 ancestor foo@e6dc8efe11cc
premerge successful
foo: versions differ -> m
picked tool ':merge' for foo (binary False symlink False changedelete False)
merging foo
my foo@6a0df1dad128+ other foo@484bf6903104 ancestor foo@e6dc8efe11cc
premerge successful
0 files updated, 2 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
contents of foo
$ cat foo
line 0
line 1
line 2-1
contents of bar
$ cat bar
line 0
line 1
line 2-2
$ cd ..