view tests/test-graft-interrupted.t @ 44363:f7459da77f23

nodemap: introduce an option to use mmap to read the nodemap mapping

The performance and memory benefit is much greater if we don't have to copy all
the data in memory for each information. So we introduce an option (on by
default) to read the data using mmap.

This changeset is the last one definition the API for index support nodemap
data. (they have to be able to use the mmaping).

Below are some benchmark comparing the best we currently have in 5.3 with the
final step of this series (using the persistent nodemap implementation in
Rust). The benchmark run `hg perfindex` with various revset and the following
variants:

Before:

 * do not use the persistent nodemap
 * use the CPython implementation of the index for nodemap
 * use mmapping of the changelog index

After:

 * use the MixedIndex Rust code, with the NodeTree object for nodemap access
   (still in review)
 * use the persistent nodemap data from disk
 * access the persistent nodemap data through mmap
 * use mmapping of the changelog index

The persistent nodemap greatly speed up  most operation on very large
repositories. Some of the previously very fast lookup end up a bit slower because
the persistent nodemap has to be setup. However the absolute slowdown is very
small and won't matters in the big picture.

Here are some numbers (in seconds) for the reference copy of mozilla-try:

Revset            Before   After     abs-change speedup

-10000:           0.004622 0.005532   0.000910  ×   0.83
-10:              0.000050 0.000132   0.000082  ×   0.37
tip               0.000052 0.000085   0.000033  ×   0.61
0 + (-10000:)     0.028222 0.005337  -0.022885  ×   5.29
0                 0.023521 0.000084  -0.023437  × 280.01
(-10000:) + 0     0.235539 0.005308  -0.230231  ×  44.37
(-10:) + :9       0.232883 0.000180  -0.232703  ×1293.79
(-10000:) + (:99) 0.238735 0.005358  -0.233377  ×  44.55
:99 + (-10000:)   0.317942 0.005593  -0.312349  ×  56.84
:9 + (-10:)       0.313372 0.000179  -0.313193  ×1750.68
:9                0.316450 0.000143  -0.316307  ×2212.93


On smaller repositories, the cost of nodemap related operation is not as big, so
the win is much more modest. Yet it helps shaving a handful of millisecond here
and there.

Here are some numbers (in seconds) for the reference copy of mercurial:

Revset            Before   After     abs-change speedup
-10:              0.000065 0.000097   0.000032  × 0.67
tip               0.000063 0.000078   0.000015  × 0.80
0                 0.000561 0.000079  -0.000482  × 7.10
-10000:           0.004609 0.003648  -0.000961  × 1.26
0 + (-10000:)     0.005023 0.003715  -0.001307  × 1.35
(-10:) + :9       0.002187 0.000108  -0.002079  ×20.25
(-10000:) + 0     0.006252 0.003716  -0.002536  × 1.68
(-10000:) + (:99) 0.006367 0.003707  -0.002660  × 1.71
:9 + (-10:)       0.003846 0.000110  -0.003736  ×34.96
:9                0.003854 0.000099  -0.003755  ×38.92
:99 + (-10000:)   0.007644 0.003778  -0.003866  × 2.02

Differential Revision: https://phab.mercurial-scm.org/D7894

#testcases abortcommand abortflag

#if abortflag
  $ cat >> $HGRCPATH <<EOF
  > [alias]
  > abort = graft --abort
  > EOF
#endif


Testing the reading of old format graftstate file with newer mercurial

  $ hg init oldgraft
  $ cd oldgraft
  $ for ch in a b c; do echo foo > $ch; hg add $ch; hg ci -Aqm "added "$ch; done;
  $ hg log -GT "{rev}:{node|short} {desc}\n"
  @  2:8be98ac1a569 added c
  |
  o  1:80e6d2c47cfe added b
  |
  o  0:f7ad41964313 added a
  
  $ hg up 0
  0 files updated, 0 files merged, 2 files removed, 0 files unresolved
  $ echo bar > b
  $ hg add b
  $ hg ci -m "bar to b"
  created new head
  $ hg graft -r 1 -r 2
  grafting 1:80e6d2c47cfe "added b"
  merging b
  warning: conflicts while merging b! (edit, then use 'hg resolve --mark')
  abort: unresolved conflicts, can't continue
  (use 'hg resolve' and 'hg graft --continue')
  [255]

Writing the nodes in old format to graftstate

  $ hg log -r 1 -r 2 -T '{node}\n' > .hg/graftstate
  $ echo foo > b
  $ hg resolve -m
  (no more unresolved files)
  continue: hg graft --continue
  $ hg graft --continue
  grafting 1:80e6d2c47cfe "added b"
  grafting 2:8be98ac1a569 "added c"

Testing that --user is preserved during conflicts and value is reused while
running `hg graft --continue`

  $ hg log -G
  @  changeset:   5:711e9fa999f1
  |  tag:         tip
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     added c
  |
  o  changeset:   4:e5ad7353b408
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     added b
  |
  o  changeset:   3:9e887f7a939c
  |  parent:      0:f7ad41964313
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     bar to b
  |
  | o  changeset:   2:8be98ac1a569
  | |  user:        test
  | |  date:        Thu Jan 01 00:00:00 1970 +0000
  | |  summary:     added c
  | |
  | o  changeset:   1:80e6d2c47cfe
  |/   user:        test
  |    date:        Thu Jan 01 00:00:00 1970 +0000
  |    summary:     added b
  |
  o  changeset:   0:f7ad41964313
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     added a
  

  $ hg up '.^^'
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved

  $ hg graft -r 1 -r 2 --user batman
  grafting 1:80e6d2c47cfe "added b"
  merging b
  warning: conflicts while merging b! (edit, then use 'hg resolve --mark')
  abort: unresolved conflicts, can't continue
  (use 'hg resolve' and 'hg graft --continue')
  [255]

  $ echo wat > b
  $ hg resolve -m
  (no more unresolved files)
  continue: hg graft --continue

  $ hg graft --continue
  grafting 1:80e6d2c47cfe "added b"
  grafting 2:8be98ac1a569 "added c"

  $ hg log -Gr 3::
  @  changeset:   7:11a36ffaacf2
  |  tag:         tip
  |  user:        batman
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     added c
  |
  o  changeset:   6:76803afc6511
  |  parent:      3:9e887f7a939c
  |  user:        batman
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     added b
  |
  | o  changeset:   5:711e9fa999f1
  | |  user:        test
  | |  date:        Thu Jan 01 00:00:00 1970 +0000
  | |  summary:     added c
  | |
  | o  changeset:   4:e5ad7353b408
  |/   user:        test
  |    date:        Thu Jan 01 00:00:00 1970 +0000
  |    summary:     added b
  |
  o  changeset:   3:9e887f7a939c
  |  parent:      0:f7ad41964313
  ~  user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     bar to b
  
Test that --date is preserved and reused in `hg graft --continue`

  $ hg up '.^^'
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ hg graft -r 1 -r 2 --date '1234560000 120'
  grafting 1:80e6d2c47cfe "added b"
  merging b
  warning: conflicts while merging b! (edit, then use 'hg resolve --mark')
  abort: unresolved conflicts, can't continue
  (use 'hg resolve' and 'hg graft --continue')
  [255]

  $ echo foobar > b
  $ hg resolve -m
  (no more unresolved files)
  continue: hg graft --continue
  $ hg graft --continue
  grafting 1:80e6d2c47cfe "added b"
  grafting 2:8be98ac1a569 "added c"

  $ hg log -Gr '.^^::.'
  @  changeset:   9:1896b76e007a
  |  tag:         tip
  |  user:        test
  |  date:        Fri Feb 13 21:18:00 2009 -0002
  |  summary:     added c
  |
  o  changeset:   8:ce2b4f1632af
  |  parent:      3:9e887f7a939c
  |  user:        test
  |  date:        Fri Feb 13 21:18:00 2009 -0002
  |  summary:     added b
  |
  o  changeset:   3:9e887f7a939c
  |  parent:      0:f7ad41964313
  ~  user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     bar to b
  
Test that --log is preserved and reused in `hg graft --continue`

  $ hg up '.^^'
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ hg graft -r 1 -r 2 --log
  grafting 1:80e6d2c47cfe "added b"
  merging b
  warning: conflicts while merging b! (edit, then use 'hg resolve --mark')
  abort: unresolved conflicts, can't continue
  (use 'hg resolve' and 'hg graft --continue')
  [255]

  $ echo foobar > b
  $ hg resolve -m
  (no more unresolved files)
  continue: hg graft --continue

  $ hg graft --continue
  grafting 1:80e6d2c47cfe "added b"
  grafting 2:8be98ac1a569 "added c"

  $ hg log -GT "{rev}:{node|short} {desc}" -r '.^^::.'
  @  11:30c1050a58b2 added c
  |  (grafted from 8be98ac1a56990c2d9ca6861041b8390af7bd6f3)
  o  10:ec7eda2313e2 added b
  |  (grafted from 80e6d2c47cfe5b3185519568327a17a061c7efb6)
  o  3:9e887f7a939c bar to b
  |
  ~

  $ cd ..

Testing the --stop flag of `hg graft` which stops the interrupted graft

  $ hg init stopgraft
  $ cd stopgraft
  $ for ch in a b c d; do echo $ch > $ch; hg add $ch; hg ci -Aqm "added "$ch; done;

  $ hg log -G
  @  changeset:   3:9150fe93bec6
  |  tag:         tip
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     added d
  |
  o  changeset:   2:155349b645be
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     added c
  |
  o  changeset:   1:5f6d8a4bf34a
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     added b
  |
  o  changeset:   0:9092f1db7931
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     added a
  
  $ hg up '.^^'
  0 files updated, 0 files merged, 2 files removed, 0 files unresolved

  $ echo foo > d
  $ hg ci -Aqm "added foo to d"

  $ hg graft --stop
  abort: no interrupted graft found
  [255]

  $ hg graft -r 3
  grafting 3:9150fe93bec6 "added d"
  merging d
  warning: conflicts while merging d! (edit, then use 'hg resolve --mark')
  abort: unresolved conflicts, can't continue
  (use 'hg resolve' and 'hg graft --continue')
  [255]

  $ hg graft --stop --continue
  abort: cannot use '--continue' and '--stop' together
  [255]

  $ hg graft --stop -U
  abort: cannot specify any other flag with '--stop'
  [255]
  $ hg graft --stop --rev 4
  abort: cannot specify any other flag with '--stop'
  [255]
  $ hg graft --stop --log
  abort: cannot specify any other flag with '--stop'
  [255]

  $ hg graft --stop
  stopped the interrupted graft
  working directory is now at a0deacecd59d

  $ hg diff

  $ hg log -Gr '.'
  @  changeset:   4:a0deacecd59d
  |  tag:         tip
  ~  parent:      1:5f6d8a4bf34a
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     added foo to d
  
  $ hg graft -r 2 -r 3
  grafting 2:155349b645be "added c"
  grafting 3:9150fe93bec6 "added d"
  merging d
  warning: conflicts while merging d! (edit, then use 'hg resolve --mark')
  abort: unresolved conflicts, can't continue
  (use 'hg resolve' and 'hg graft --continue')
  [255]

  $ hg graft --stop
  stopped the interrupted graft
  working directory is now at 75b447541a9e

  $ hg diff

  $ hg log -G -T "{rev}:{node|short} {desc}"
  @  5:75b447541a9e added c
  |
  o  4:a0deacecd59d added foo to d
  |
  | o  3:9150fe93bec6 added d
  | |
  | o  2:155349b645be added c
  |/
  o  1:5f6d8a4bf34a added b
  |
  o  0:9092f1db7931 added a
  
  $ cd ..

Testing the --abort flag for `hg graft` which aborts and rollback to state
before the graft

  $ hg init abortgraft
  $ cd abortgraft
  $ for ch in a b c d; do echo $ch > $ch; hg add $ch; hg ci -Aqm "added "$ch; done;

  $ hg up '.^^'
  0 files updated, 0 files merged, 2 files removed, 0 files unresolved

  $ echo x > x
  $ hg ci -Aqm "added x"
  $ hg up '.^'
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ echo foo > c
  $ hg ci -Aqm "added foo to c"

  $ hg log -GT "{rev}:{node|short} {desc}"
  @  5:36b793615f78 added foo to c
  |
  | o  4:863a25e1a9ea added x
  |/
  | o  3:9150fe93bec6 added d
  | |
  | o  2:155349b645be added c
  |/
  o  1:5f6d8a4bf34a added b
  |
  o  0:9092f1db7931 added a
  
  $ hg up 9150fe93bec6
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ hg abort
  abort: no interrupted graft to abort (abortflag !)
  abort: no operation in progress (abortcommand !)
  [255]

when stripping is required
  $ hg graft -r 4 -r 5
  grafting 4:863a25e1a9ea "added x"
  grafting 5:36b793615f78 "added foo to c" (tip)
  merging c
  warning: conflicts while merging c! (edit, then use 'hg resolve --mark')
  abort: unresolved conflicts, can't continue
  (use 'hg resolve' and 'hg graft --continue')
  [255]

  $ hg graft --continue --abort
  abort: cannot use '--continue' and '--abort' together
  [255]

  $ hg graft --abort --stop
  abort: cannot use '--abort' and '--stop' together
  [255]

  $ hg graft --abort --currentuser
  abort: cannot specify any other flag with '--abort'
  [255]

  $ hg graft --abort --edit
  abort: cannot specify any other flag with '--abort'
  [255]

#if abortcommand
when in dry-run mode
  $ hg abort --dry-run
  graft in progress, will be aborted
#endif

  $ hg abort
  graft aborted
  working directory is now at 9150fe93bec6
  $ hg log -GT "{rev}:{node|short} {desc}"
  o  5:36b793615f78 added foo to c
  |
  | o  4:863a25e1a9ea added x
  |/
  | @  3:9150fe93bec6 added d
  | |
  | o  2:155349b645be added c
  |/
  o  1:5f6d8a4bf34a added b
  |
  o  0:9092f1db7931 added a
  
when stripping is not required
  $ hg graft -r 5
  grafting 5:36b793615f78 "added foo to c" (tip)
  merging c
  warning: conflicts while merging c! (edit, then use 'hg resolve --mark')
  abort: unresolved conflicts, can't continue
  (use 'hg resolve' and 'hg graft --continue')
  [255]

  $ hg abort
  graft aborted
  working directory is now at 9150fe93bec6
  $ hg log -GT "{rev}:{node|short} {desc}"
  o  5:36b793615f78 added foo to c
  |
  | o  4:863a25e1a9ea added x
  |/
  | @  3:9150fe93bec6 added d
  | |
  | o  2:155349b645be added c
  |/
  o  1:5f6d8a4bf34a added b
  |
  o  0:9092f1db7931 added a
  
when some of the changesets became public

  $ hg graft -r 4 -r 5
  grafting 4:863a25e1a9ea "added x"
  grafting 5:36b793615f78 "added foo to c" (tip)
  merging c
  warning: conflicts while merging c! (edit, then use 'hg resolve --mark')
  abort: unresolved conflicts, can't continue
  (use 'hg resolve' and 'hg graft --continue')
  [255]

  $ hg log -GT "{rev}:{node|short} {desc}"
  @  6:6ec71c037d94 added x
  |
  | %  5:36b793615f78 added foo to c
  | |
  | | o  4:863a25e1a9ea added x
  | |/
  o |  3:9150fe93bec6 added d
  | |
  o |  2:155349b645be added c
  |/
  o  1:5f6d8a4bf34a added b
  |
  o  0:9092f1db7931 added a
  
  $ hg phase -r 6 --public

  $ hg abort
  cannot clean up public changesets 6ec71c037d94
  graft aborted
  working directory is now at 6ec71c037d94

when we created new changesets on top of existing one

  $ hg up '.^^'
  0 files updated, 0 files merged, 2 files removed, 0 files unresolved
  $ echo y > y
  $ hg ci -Aqm "added y"
  $ echo z > z
  $ hg ci -Aqm "added z"

  $ hg up 3
  1 files updated, 0 files merged, 3 files removed, 0 files unresolved
  $ hg log -GT "{rev}:{node|short} {desc}"
  o  8:637f9e9bbfd4 added z
  |
  o  7:123221671fd4 added y
  |
  | o  6:6ec71c037d94 added x
  | |
  | | o  5:36b793615f78 added foo to c
  | | |
  | | | o  4:863a25e1a9ea added x
  | | |/
  | @ |  3:9150fe93bec6 added d
  |/ /
  o /  2:155349b645be added c
  |/
  o  1:5f6d8a4bf34a added b
  |
  o  0:9092f1db7931 added a
  
  $ hg graft -r 8 -r 7 -r 5
  grafting 8:637f9e9bbfd4 "added z" (tip)
  grafting 7:123221671fd4 "added y"
  grafting 5:36b793615f78 "added foo to c"
  merging c
  warning: conflicts while merging c! (edit, then use 'hg resolve --mark')
  abort: unresolved conflicts, can't continue
  (use 'hg resolve' and 'hg graft --continue')
  [255]

  $ cd ..
  $ hg init pullrepo
  $ cd pullrepo
  $ cat >> .hg/hgrc <<EOF
  > [phases]
  > publish=False
  > EOF
  $ hg pull ../abortgraft --config phases.publish=False
  pulling from ../abortgraft
  requesting all changes
  adding changesets
  adding manifests
  adding file changes
  added 11 changesets with 9 changes to 8 files (+4 heads)
  new changesets 9092f1db7931:6b98ff0062dd (6 drafts)
  (run 'hg heads' to see heads, 'hg merge' to merge)
  $ hg up 9
  5 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo w > w
  $ hg ci -Aqm "added w" --config phases.publish=False

  $ cd ../abortgraft
  $ hg pull ../pullrepo
  pulling from ../pullrepo
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 1 changesets with 1 changes to 1 files (+1 heads)
  new changesets 311dfc6cf3bf (1 drafts)
  (run 'hg heads .' to see heads, 'hg merge' to merge)

  $ hg abort
  new changesets detected on destination branch, can't strip
  graft aborted
  working directory is now at 6b98ff0062dd

  $ cd ..

============================
Testing --no-commit option:|
============================

  $ hg init nocommit
  $ cd nocommit
  $ echo a > a
  $ hg ci -qAma
  $ echo b > b
  $ hg ci -qAmb
  $ hg up -q 0
  $ echo c > c
  $ hg ci -qAmc
  $ hg log -GT "{rev}:{node|short} {desc}\n"
  @  2:d36c0562f908 c
  |
  | o  1:d2ae7f538514 b
  |/
  o  0:cb9a9f314b8b a
  

Check reporting when --no-commit used with non-applicable options:

  $ hg graft 1 --no-commit -e
  abort: cannot specify --no-commit and --edit together
  [255]

  $ hg graft 1 --no-commit --log
  abort: cannot specify --no-commit and --log together
  [255]

  $ hg graft 1 --no-commit -D
  abort: cannot specify --no-commit and --currentdate together
  [255]

Test --no-commit is working:
  $ hg graft 1 --no-commit
  grafting 1:d2ae7f538514 "b"

  $ hg log -GT "{rev}:{node|short} {desc}\n"
  @  2:d36c0562f908 c
  |
  | o  1:d2ae7f538514 b
  |/
  o  0:cb9a9f314b8b a
  

  $ hg diff
  diff -r d36c0562f908 b
  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
  +++ b/b	Thu Jan 01 00:00:00 1970 +0000
  @@ -0,0 +1,1 @@
  +b

Prepare wrdir to check --no-commit is resepected after --continue:

  $ hg up -qC
  $ echo A>a
  $ hg ci -qm "A in file a"
  $ hg up -q 1
  $ echo B>a
  $ hg ci -qm "B in file a"
  $ hg log -GT "{rev}:{node|short} {desc}\n"
  @  4:2aa9ad1006ff B in file a
  |
  | o  3:09e253b87e17 A in file a
  | |
  | o  2:d36c0562f908 c
  | |
  o |  1:d2ae7f538514 b
  |/
  o  0:cb9a9f314b8b a
  

  $ hg graft 3 --no-commit
  grafting 3:09e253b87e17 "A in file a"
  merging a
  warning: conflicts while merging a! (edit, then use 'hg resolve --mark')
  abort: unresolved conflicts, can't continue
  (use 'hg resolve' and 'hg graft --continue')
  [255]

Resolve conflict:
  $ echo A>a
  $ hg resolve --mark
  (no more unresolved files)
  continue: hg graft --continue

  $ hg graft --continue
  grafting 3:09e253b87e17 "A in file a"
  $ hg log -GT "{rev}:{node|short} {desc}\n"
  @  4:2aa9ad1006ff B in file a
  |
  | %  3:09e253b87e17 A in file a
  | |
  | o  2:d36c0562f908 c
  | |
  o |  1:d2ae7f538514 b
  |/
  o  0:cb9a9f314b8b a
  
  $ hg diff
  diff -r 2aa9ad1006ff a
  --- a/a	Thu Jan 01 00:00:00 1970 +0000
  +++ b/a	Thu Jan 01 00:00:00 1970 +0000
  @@ -1,1 +1,1 @@
  -B
  +A

  $ hg up -qC

Check --no-commit is resepected when passed with --continue:

  $ hg graft 3
  grafting 3:09e253b87e17 "A in file a"
  merging a
  warning: conflicts while merging a! (edit, then use 'hg resolve --mark')
  abort: unresolved conflicts, can't continue
  (use 'hg resolve' and 'hg graft --continue')
  [255]

Resolve conflict:
  $ echo A>a
  $ hg resolve --mark
  (no more unresolved files)
  continue: hg graft --continue

  $ hg graft --continue --no-commit
  grafting 3:09e253b87e17 "A in file a"
  $ hg diff
  diff -r 2aa9ad1006ff a
  --- a/a	Thu Jan 01 00:00:00 1970 +0000
  +++ b/a	Thu Jan 01 00:00:00 1970 +0000
  @@ -1,1 +1,1 @@
  -B
  +A

  $ hg log -GT "{rev}:{node|short} {desc}\n"
  @  4:2aa9ad1006ff B in file a
  |
  | %  3:09e253b87e17 A in file a
  | |
  | o  2:d36c0562f908 c
  | |
  o |  1:d2ae7f538514 b
  |/
  o  0:cb9a9f314b8b a
  
  $ hg up -qC

Test --no-commit when graft multiple revisions:
When there is conflict:
  $ hg graft -r "2::3" --no-commit
  grafting 2:d36c0562f908 "c"
  grafting 3:09e253b87e17 "A in file a"
  merging a
  warning: conflicts while merging a! (edit, then use 'hg resolve --mark')
  abort: unresolved conflicts, can't continue
  (use 'hg resolve' and 'hg graft --continue')
  [255]

  $ echo A>a
  $ hg resolve --mark
  (no more unresolved files)
  continue: hg graft --continue
  $ hg graft --continue
  grafting 3:09e253b87e17 "A in file a"
  $ hg diff
  diff -r 2aa9ad1006ff a
  --- a/a	Thu Jan 01 00:00:00 1970 +0000
  +++ b/a	Thu Jan 01 00:00:00 1970 +0000
  @@ -1,1 +1,1 @@
  -B
  +A
  diff -r 2aa9ad1006ff c
  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
  +++ b/c	Thu Jan 01 00:00:00 1970 +0000
  @@ -0,0 +1,1 @@
  +c

  $ hg log -GT "{rev}:{node|short} {desc}\n"
  @  4:2aa9ad1006ff B in file a
  |
  | %  3:09e253b87e17 A in file a
  | |
  | o  2:d36c0562f908 c
  | |
  o |  1:d2ae7f538514 b
  |/
  o  0:cb9a9f314b8b a
  
  $ hg up -qC

When there is no conflict:
  $ echo d>d
  $ hg add d -q
  $ hg ci -qmd
  $ hg up 3 -q
  $ hg log -GT "{rev}:{node|short} {desc}\n"
  o  5:baefa8927fc0 d
  |
  o  4:2aa9ad1006ff B in file a
  |
  | @  3:09e253b87e17 A in file a
  | |
  | o  2:d36c0562f908 c
  | |
  o |  1:d2ae7f538514 b
  |/
  o  0:cb9a9f314b8b a
  

  $ hg graft -r 1 -r 5 --no-commit
  grafting 1:d2ae7f538514 "b"
  grafting 5:baefa8927fc0 "d" (tip)
  $ hg diff
  diff -r 09e253b87e17 b
  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
  +++ b/b	Thu Jan 01 00:00:00 1970 +0000
  @@ -0,0 +1,1 @@
  +b
  diff -r 09e253b87e17 d
  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
  +++ b/d	Thu Jan 01 00:00:00 1970 +0000
  @@ -0,0 +1,1 @@
  +d
  $ hg log -GT "{rev}:{node|short} {desc}\n"
  o  5:baefa8927fc0 d
  |
  o  4:2aa9ad1006ff B in file a
  |
  | @  3:09e253b87e17 A in file a
  | |
  | o  2:d36c0562f908 c
  | |
  o |  1:d2ae7f538514 b
  |/
  o  0:cb9a9f314b8b a
  
  $ cd ..