branchcache: add a "pure topological head" fast path
In a narrow but actually quick common case, all topological heads are all on
the same branch and all open. In this case, computing the branch map is very
simple. We can quickly detect situation where this situation will not change.
So we update the V3 format to be able to express this situation and upgrade the
update code to detect we remains in that mode.
The branch cache is populated with the actual value when the branch map is
accessed, but the update_disk method can do the update without needing to
populate it.
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Test file dedicated to checking side-data related behavior
==========================================================
Check data can be written/read from sidedata
============================================
$ cat << EOF >> $HGRCPATH
> [extensions]
> testsidedata=$TESTDIR/testlib/ext-sidedata.py
> EOF
$ hg init test-sidedata --config experimental.revlogv2=enable-unstable-format-and-corrupt-my-data
$ cd test-sidedata
$ echo aaa > a
$ hg add a
$ hg commit -m a --traceback
$ echo aaa > b
$ hg add b
$ hg commit -m b
$ echo xxx >> a
$ hg commit -m aa
$ hg debugsidedata -c 0
2 sidedata entries
entry-0001 size 4
entry-0002 size 32
$ hg debugsidedata -c 1 -v
2 sidedata entries
entry-0001 size 4
'\x00\x00\x006'
entry-0002 size 32
'\x98\t\xf9\xc4v\xf0\xc5P\x90\xf7wRf\xe8\xe27e\xfc\xc1\x93\xa4\x96\xd0\x1d\x97\xaaG\x1d\xd7t\xfa\xde'
$ hg debugsidedata -m 2
2 sidedata entries
entry-0001 size 4
entry-0002 size 32
$ hg debugsidedata a 1
2 sidedata entries
entry-0001 size 4
entry-0002 size 32
$ hg debug-revlog-index --verbose -c
rev rank linkrev nodeid p1-rev p1-nodeid p2-rev p2-nodeid full-size delta-base flags comp-mode data-offset chunk-size sd-comp-mode sidedata-offset sd-chunk-size
0 -1 0 7049e48789d7 -1 000000000000 -1 000000000000 54 0 0 0 0 54 plain 0 90
1 -1 1 2707720c6597 0 7049e48789d7 -1 000000000000 54 1 0 0 54 54 plain 90 90
2 -1 2 40f977031323 1 2707720c6597 -1 000000000000 55 2 0 0 108 55 plain 180 90
$ hg debug-revlog-index --verbose -m
rev rank linkrev nodeid p1-rev p1-nodeid p2-rev p2-nodeid full-size delta-base flags comp-mode data-offset chunk-size sd-comp-mode sidedata-offset sd-chunk-size
0 -1 0 b85d294330e3 -1 000000000000 -1 000000000000 43 0 0 0 0 43 plain 0 90
1 -1 1 1a0aec305c63 0 b85d294330e3 -1 000000000000 86 0 0 0 43 55 plain 90 90
2 -1 2 104258a4f75f 1 1a0aec305c63 -1 000000000000 86 1 0 0 98 55 plain 180 90
Check upgrade behavior
======================
Right now, sidedata has not upgrade support
Check that we can upgrade to sidedata
-------------------------------------
$ hg init up-no-side-data --config experimental.revlogv2=no
$ hg debugformat -v -R up-no-side-data | grep -E 'changelog-v2|revlog-v2'
revlog-v2: no no no
changelog-v2: no no no
$ hg debugformat -v -R up-no-side-data --config experimental.revlogv2=enable-unstable-format-and-corrupt-my-data | grep -E 'changelog-v2|revlog-v2'
revlog-v2: no yes no
changelog-v2: no no no
$ hg debugupgraderepo -R up-no-side-data --config experimental.revlogv2=enable-unstable-format-and-corrupt-my-data > /dev/null
Check that we can downgrade from sidedata
-----------------------------------------
$ hg init up-side-data --config experimental.revlogv2=enable-unstable-format-and-corrupt-my-data
$ hg debugformat -v -R up-side-data | grep -E 'changelog-v2|revlog-v2'
revlog-v2: yes no no
changelog-v2: no no no
$ hg debugformat -v -R up-side-data --config experimental.revlogv2=no | grep -E 'changelog-v2|revlog-v2'
revlog-v2: yes no no
changelog-v2: no no no
$ hg debugupgraderepo -R up-side-data --config experimental.revlogv2=no > /dev/null