tests/test-merge-halt.t

dirstate-tree: Avoid BTreeMap double-lookup when inserting a dirstate entry

The child nodes of a given node in the tree-shaped dirstate are kept in a
`BTreeMap` where keys are file names as strings. Finding or inserting a value
in the map takes `O(log(n))` string comparisons, which adds up when constructing
the tree.

The `entry` API allows finding a "spot" in the map that may or may not be
occupied and then access that value or insert a new one without doing map
lookup again. However the current API is limited in that calling `entry`
requires an owned key (and so a memory allocation), even if it ends up not
being used in the case where the map already has a value with an equal key.

This is still a win, with 4% better end-to-end time for `hg status` measured
here with hyperfine:

```
Benchmark #1: ../hg2/hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1
  Time (mean ± σ):      1.337 s ±  0.018 s    [User: 892.9 ms, System: 437.5 ms]
  Range (min … max):    1.316 s …  1.373 s    10 runs

Benchmark #2: ./hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1
  Time (mean ± σ):      1.291 s ±  0.008 s    [User: 853.4 ms, System: 431.1 ms]
  Range (min … max):    1.283 s …  1.309 s    10 runs

Summary
  './hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1' ran
    1.04 ± 0.02 times faster than '../hg2/hg status -R $REPO --config=experimental.dirstate-tree.in-memory=1'
```

* ./hg is this revision
* ../hg2/hg is its parent
* $REPO is an old snapshot of mozilla-central

Differential Revision: https://phab.mercurial-scm.org/D10550

  $ cat >> $HGRCPATH <<EOF
  > [extensions]
  > rebase=
  > [phases]
  > publish=False
  > [merge]
  > EOF

  $ hg init repo
  $ cd repo
  $ echo a > a
  $ echo b > b
  $ hg commit -qAm ab
  $ echo c >> a
  $ echo c >> b
  $ hg commit -qAm c
  $ hg up -q ".^"
  $ echo d >> a
  $ echo d >> b
  $ hg commit -qAm d

Testing on-failure=continue
  $ echo on-failure=continue >> $HGRCPATH
  $ hg rebase -s 1 -d 2 --tool false
  rebasing 1:1f28a51c3c9b "c"
  merging a
  merging b
  merging a failed!
  merging b failed!
  unresolved conflicts (see 'hg resolve', then 'hg rebase --continue')
  [240]

  $ hg resolve --list
  U a
  U b

  $ hg rebase --abort
  rebase aborted

Testing on-failure=halt
  $ echo on-failure=halt >> $HGRCPATH
  $ hg rebase -s 1 -d 2 --tool false
  rebasing 1:1f28a51c3c9b "c"
  merging a
  merging b
  merging a failed!
  merge halted after failed merge (see hg resolve)
  [240]

  $ hg resolve --list
  U a
  U b

  $ hg rebase --abort
  rebase aborted

Testing on-failure=prompt
  $ cat <<EOS >> $HGRCPATH
  > [merge]
  > on-failure=prompt
  > [ui]
  > interactive=1
  > EOS
  $ cat <<EOS | hg rebase -s 1 -d 2 --tool false
  > y
  > n
  > EOS
  rebasing 1:1f28a51c3c9b "c"
  merging a
  merging b
  merging a failed!
  continue merge operation (yn)? y
  merging b failed!
  continue merge operation (yn)? n
  merge halted after failed merge (see hg resolve)
  [240]

  $ hg resolve --list
  U a
  U b

  $ hg rebase --abort
  rebase aborted

Check that successful tool with failed post-check halts the merge
  $ cat <<EOS >> $HGRCPATH
  > [merge-tools]
  > true.check=changed
  > EOS
  $ cat <<EOS | hg rebase -s 1 -d 2 --tool true
  > y
  > n
  > n
  > EOS
  rebasing 1:1f28a51c3c9b "c"
  merging a
  merging b
   output file a appears unchanged
  was merge successful (yn)? y
   output file b appears unchanged
  was merge successful (yn)? n
  merging b failed!
  continue merge operation (yn)? n
  merge halted after failed merge (see hg resolve)
  [240]

  $ hg resolve --list
  R a
  U b

  $ hg rebase --abort
  rebase aborted

Check that conflicts with conflict check also halts the merge
  $ cat <<EOS >> $HGRCPATH
  > [merge-tools]
  > true.check=conflicts
  > true.premerge=keep
  > [merge]
  > on-failure=halt
  > EOS
  $ hg rebase -s 1 -d 2 --tool true
  rebasing 1:1f28a51c3c9b "c"
  merging a
  merging b
  merging a failed!
  merge halted after failed merge (see hg resolve)
  [240]

  $ hg resolve --list
  U a
  U b

  $ hg rebase --abort
  rebase aborted

Check that always-prompt also can halt the merge
  $ cat <<EOS | hg rebase -s 1 -d 2 --tool true --config merge-tools.true.check=prompt
  > y
  > n
  > EOS
  rebasing 1:1f28a51c3c9b "c"
  merging a
  merging b
  was merge of 'a' successful (yn)? y
  was merge of 'b' successful (yn)? n
  merging b failed!
  merge halted after failed merge (see hg resolve)
  [240]

  $ hg resolve --list
  R a
  U b

  $ hg rebase --abort
  rebase aborted

Check that successful tool otherwise allows the merge to continue
  $ hg rebase -s 1 -d 2 --tool echo --keep --config merge-tools.echo.premerge=keep
  rebasing 1:1f28a51c3c9b "c"
  merging a
  merging b
  $TESTTMP/repo/a *a~base* *a~other* (glob)
  $TESTTMP/repo/b *b~base* *b~other* (glob)