branchcache: use an explicit class for the v2 version
This prepare the introduction of an experimental v3 format version.
In the process, we move the description of the format in that new class.
$ hg init test-content
$ cd test-content
$ hg debugbuilddag '+2*2*3*4+7'
$ hg bookmark -r 1 @
$ hg log -G --template '{rev}:{node|short}'
o 11:1d876b1f862c
|
o 10:ea5f71948eb8
|
o 9:f1b0356d867a
|
o 8:e8d1253fb0d7
|
o 7:d423bbba4459
|
o 6:a2f58e9c1e56
|
o 5:3a367db1fabc
|
o 4:e7bd5218ca15
|
| o 3:6100d3090acf
|/
| o 2:fa942426a6fd
|/
| o 1:66f7d451a68b
|/
o 0:1ea73414a91b
$ hg --config extensions.closehead= close-head -m 'Not a head' 0 1
abort: revision is not an open head: 0
[255]
$ hg --config extensions.closehead= close-head -m 'Not a head' -r 0 1
abort: revision is not an open head: 0
[255]
$ hg id
000000000000
$ hg --config extensions.closehead= close-head -m 'Close old heads' -r 1 2
$ hg id
000000000000
$ hg bookmark
@ 1:66f7d451a68b
$ hg heads
changeset: 11:1d876b1f862c
user: debugbuilddag
date: Thu Jan 01 00:00:11 1970 +0000
summary: r11
changeset: 3:6100d3090acf
parent: 0:1ea73414a91b
user: debugbuilddag
date: Thu Jan 01 00:00:03 1970 +0000
summary: r3
$ hg --config extensions.closehead= close-head -m 'Close more old heads' -r 11
$ hg heads
changeset: 3:6100d3090acf
parent: 0:1ea73414a91b
user: debugbuilddag
date: Thu Jan 01 00:00:03 1970 +0000
summary: r3
$ hg --config extensions.closehead= close-head -m 'Not a head' 0
abort: revision is not an open head: 0
[255]
$ hg --config extensions.closehead= close-head -m 'Already closed head' 1
abort: revision is not an open head: 1
[255]
$ hg init ../test-empty
$ cd ../test-empty
$ hg debugbuilddag '+1'
$ hg log -G --template '{rev}:{node|short}'
o 0:1ea73414a91b
$ hg --config extensions.closehead= close-head -m 'Close initial revision' 0
$ hg heads
[1]