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 a
$ cd a
$ touch empty1
$ hg add empty1
$ hg commit -m 'add empty1'
$ touch empty2
$ hg add empty2
$ hg commit -m 'add empty2'
$ hg up -C 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ touch empty3
$ hg add empty3
$ hg commit -m 'add empty3'
created new head
$ hg heads
changeset: 2:a1cb177e0d44
tag: tip
parent: 0:1e1d9c4e5b64
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: add empty3
changeset: 1:097d2b0e17f6
user: test
date: Thu Jan 01 00:00:00 1970 +0000
summary: add empty2
$ hg merge 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
Before changeset 05257fd28591, we didn't notice the
empty file that came from rev 1:
$ hg status
M empty2
$ hg commit -m merge
$ hg manifest --debug tip
b80de5d138758541c5f05265ad144ab9fa86d1db 644 empty1
b80de5d138758541c5f05265ad144ab9fa86d1db 644 empty2
b80de5d138758541c5f05265ad144ab9fa86d1db 644 empty3
$ cd ..