tests/test-remotefilelog-wireproto.t

commit: improve the files field of changelog for merges

Currently, the files list of merge commits repeats all the deletions
(either actual deletions, or files that got renamed) that happened
between base and p2 of the merge. If p2 is the main branch, the list
can easily be much bigger than the change being merged.

This results in various problems worth improving:
- changelog is bigger than necessary
- `hg log directory` lists many unrelated merge commits, and `hg log
  -v -r commit` frequently fills multiple screens worth of files
- it possibly slows down adjustlinkrev, by forcing it to read more
  manifests, and that function can certainly be a bottleneck
- the server side of pulls can waste a lot of time simply opening the
  filelogs for pointless files (the constant factors for opening even
  a tiny filelog is apparently pretty bad)

So stop listing such files as described in the code.  Impacted merge
commits and their descendants get a different hash than they would
have without this. This doesn't seem problematic, except for
convert. The previous commit helped with that in the hg->hg case (but
if you do svn->hg twice from scratch, hashes can still change).

The rest of the description is numbers. I don't have much to report,
because recreating the files list of existing repositories is not
easy:
- debugupgradeformat and bundle/unbundle don't recreate the list
- export/import tends to choke quickly applying patches or on
  description that contain diffs,
- merge commits from the convert extension don't have the right files
  list for reasons orthogonal to the current commit
- replaying the merge with hg update/hg merge/hg revert --all/hg
  commit can end up failing in hg revert
- I wasn't sure that using debugsetparents + debugrebuilddirstate
  would really build the right thing

I measured commit time before and after this change, in a case with no
files filtered out, several files filtered out (no difference) and 5k
files filtered out (+1% time).

Recreating the 100 more recent merges in a private repo, the
concatenated uncompressed files lists goes from 1.12MB to
0.52MB. Excluding 3 merges that are not representative, then the size
goes from 570k to 15k.
I converted part of mozilla-central, and observed file list shrinking
quite a bit too, starting at the very first merge, 733641d9feaf, going
from 550 files to 10 files (although they have relatively few merges,
so they probably wouldn't care).

Differential Revision: https://phab.mercurial-scm.org/D6613

#require no-windows

  $ . "$TESTDIR/remotefilelog-library.sh"

  $ hg init master
  $ cd master
  $ cat >> .hg/hgrc <<EOF
  > [remotefilelog]
  > server=True
  > EOF
  $ echo x > x
  $ hg commit -qAm x
  $ echo y >> x
  $ hg commit -qAm y
  $ echo z >> x
  $ hg commit -qAm z
  $ hg update 1
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo w >> x
  $ hg commit -qAm w

  $ cd ..

Shallow clone and activate getflogheads testing extension

  $ hgcloneshallow ssh://user@dummy/master shallow --noupdate
  streaming all changes
  2 files to transfer, 908 bytes of data
  transferred 908 bytes in * seconds (*/sec) (glob)
  searching for changes
  no changes found
  $ cd shallow

  $ cat >> .hg/hgrc <<EOF
  > [extensions]
  > getflogheads=$TESTDIR/remotefilelog-getflogheads.py
  > EOF

Get heads of a remotefilelog

  $ hg getflogheads x
  2797809ca5e9c2f307d82b1345e832f655fb99a2
  ca758b402ddc91e37e3113e1a97791b537e1b7bb

Get heads of a non-existing remotefilelog

  $ hg getflogheads y
  EMPTY