changing-files: rework the way we store changed files in side-data
We need to store new data so this is a good opportunity to rework this fully.
1) We directly store the list of affected file in the side data:
* This avoid having to fetch and parse the `files` list in the revision in
addition to the sidedata. Making the data more self sufficient.
* This work around situation where that `files` field contains wrong
information, and open the way to other bug fixing (eg:
issue6219)
* The format (fixed initial index, sorted files) allow for fast lookup of
filename within the structure.
* This unify the storage of affected files and copies sources and destination,
limiting the number filename stored redundantly.
* This prepare for the fact we should drop the `files` as soon as we do any
change affecting the revision schema.
* This rely on compression to avoid a significant increase of the changelog.d.
More testing on this will be done before we freeze the final format.
2) We can store additional data:
* The new "merged" field,
* A future "salvaged" set recording files that might have been deleted but have
were still present in the final result.
Differential Revision: https://phab.mercurial-scm.org/D9090
$ hg init
$ echo 123 > a
$ hg add a
$ hg commit -m "first" a
$ mkdir sub
$ echo 321 > sub/b
$ hg add sub/b
$ hg commit -m "second" sub/b
$ cat sub/b
321
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
$ cat sub/b 2>/dev/null || echo "sub/b not present"
sub/b not present
$ test -d sub || echo "sub not present"
sub not present