tests/test-bookmarks-rebase.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

  $ echo "[extensions]" >> $HGRCPATH
  $ echo "rebase=" >> $HGRCPATH

initialize repository

  $ hg init

  $ echo 'a' > a
  $ hg ci -A -m "0"
  adding a

  $ echo 'b' > b
  $ hg ci -A -m "1"
  adding b

  $ hg up 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ echo 'c' > c
  $ hg ci -A -m "2"
  adding c
  created new head

  $ echo 'd' > d
  $ hg ci -A -m "3"
  adding d

  $ hg bookmark -r 1 one
  $ hg bookmark -r 3 two
  $ hg up -q two

bookmark list

  $ hg bookmark
     one                       1:925d80f479bb
   * two                       3:2ae46b1d99a7

rebase

  $ hg rebase -s two -d one
  rebasing 3:2ae46b1d99a7 "3" (two tip)
  saved backup bundle to $TESTTMP/.hg/strip-backup/2ae46b1d99a7-e6b057bc-rebase.hg

  $ hg log
  changeset:   3:42e5ed2cdcf4
  bookmark:    two
  tag:         tip
  parent:      1:925d80f479bb
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     3
  
  changeset:   2:db815d6d32e6
  parent:      0:f7b1eb17ad24
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     2
  
  changeset:   1:925d80f479bb
  bookmark:    one
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     1
  
  changeset:   0:f7b1eb17ad24
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     0
  
aborted rebase should restore active bookmark.

  $ hg up 1
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (leaving bookmark two)
  $ echo 'e' > d
  $ hg ci -A -m "4"
  adding d
  created new head
  $ hg bookmark three
  $ hg rebase -s three -d two
  rebasing 4:dd7c838e8362 "4" (three tip)
  merging d
  warning: conflicts while merging d! (edit, then use 'hg resolve --mark')
  unresolved conflicts (see hg resolve, then hg rebase --continue)
  [1]
  $ hg rebase --abort
  rebase aborted
  $ hg bookmark
     one                       1:925d80f479bb
   * three                     4:dd7c838e8362
     two                       3:42e5ed2cdcf4

after aborted rebase, restoring a bookmark that has been removed should not fail

  $ hg rebase -s three -d two
  rebasing 4:dd7c838e8362 "4" (three tip)
  merging d
  warning: conflicts while merging d! (edit, then use 'hg resolve --mark')
  unresolved conflicts (see hg resolve, then hg rebase --continue)
  [1]
  $ hg bookmark -d three
  $ hg rebase --abort
  rebase aborted
  $ hg bookmark
     one                       1:925d80f479bb
     two                       3:42e5ed2cdcf4