annotate tests/test-backout.t @ 49777:e1953a34c110

bundle: emit full snapshot as is, without doing a redelta

With the new `forced` delta-reused policy, it become important to be able to
send full snapshot where full snapshot are needed. Otherwise, the fallback delta
will simply be used on the client side… creating monstrous delta chain, since
revision that are meant as a reset of delta-chain chain becoming too complex are
simply adding a new full delta-tree on the leaf of another one.

In the `non-forced` cases, client process full snapshot from the bundle
differently from deltas, so client will still try to convert the full snapshot
into a delta if possible. So this will no lead to pathological storage
explosion.

I have considered making this configurable, but the impact seems limited enough
that it does not seems to be worth it. Especially with the current
sparse-revlog format that use "delta-tree" with multiple level snapshots, full
snapshot are much less frequent and not that different from other intermediate
snapshot that we are already sending over the wire anyway.

CPU wise, this will help the bundling side a little as it will not need to
reconstruct revisions and compute deltas. The unbundling side might save a tiny
amount of CPU as it won't need to reconstruct the delta-base to reconstruct the
revision full text. This only slightly visible in some of the benchmarks. And
have no real impact on most of them.

### data-env-vars.name      = pypy-2018-08-01-zstd-sparse-revlog
  # benchmark.name          = perf-bundle
  # benchmark.variants.revs = last-40000
before:          11.467186 seconds
just-emit-full:  11.190576 seconds   (-2.41%)
with-pull-force: 11.041091 seconds   (-3.72%)
  # benchmark.name          = perf-unbundle
  # benchmark.variants.revs = last-40000
before:     16.744862
just-emit-full:: 16.561036 seconds   (-1.10%)
with-pull-force: 16.389344 seconds   (-2.12%)
  # benchmark.name          = pull
  # benchmark.variants.revs = last-40000
before:     26.870569
just-emit-full:  26.391188 seconds   (-1.78%)
with-pull-force: 25.633184 seconds   (-4.60%)


Space wise (so network-wise) the impact is fairly small. When taking compression into
account.

Below are tests the size of `hg bundle --all` for a handful of benchmark repositories
(with bzip, zstd compression and without it)

This show a small increase in the bundle size, but nothing really significant
except maybe for mozilla-try (+12%) that nobody really pulls large chunk of anyway.
Mozilla-try is also the repository that benefit the most for not having to
recompute deltas client size.

### mercurial:
bzip-before:     26 406 342 bytes
bzip-after:      26 691 543 bytes  +1.08%

zstd-before:     27 918 645 bytes
zstd-after:      28 075 896 bytes  +0.56%

none-before:     98 675 601 bytes
none-after:     100 411 237 bytes  +1.76%


### pypy
bzip-before:    201 295 752 bytes
bzip-after:     209 780 282 bytes  +4.21%

zstd-before:    202 974 795 bytes
zstd-after:     205 165 780 bytes  +1.08%

none-before:    871 070 261 bytes
none-after:     993 595 057 bytes +14.07%


### netbeans
bzip-before:    601 314 330 bytes
bzip-after:     614 246 241 bytes  +2.15%

zstd-before:    604 745 136 bytes
zstd-after:     615 497 705 bytes  +1.78%

none-before:  3 338 238 571 bytes
none-after:   3 439 422 535 bytes  +3.03%


### mozilla-central
bzip-before:  1 493 006 921 bytes
bzip-after:   1 549 650 570 bytes  +3.79%

zstd-before:  1 481 910 102 bytes
zstd-after:   1 513 052 415 bytes  +2.10%

none-before:  6 535 929 910 bytes
none-after:   7 010 191 342 bytes  +7.26%


### mozilla-try
bzip-before:  6 583 425 999 bytes
bzip-after:   7 423 536 928 bytes +12.76%

zstd-before:  6 021 009 212 bytes
zstd-after:   6 674 922 420 bytes +10.86%

none-before: 22 954 739 558 bytes
none-after:  26 013 854 771 bytes +13.32%

  $ hg init basic
  $ cd basic

should complain

  $ hg backout
  abort: please specify a revision to backout
  [10]
  $ hg backout -r 0 0
  abort: please specify just one revision
  [10]

basic operation
(this also tests that editor is invoked if the commit message is not
specified explicitly)

  $ echo a > a
  $ hg commit -d '0 0' -A -m a
  adding a
  $ echo b >> a
  $ hg commit -d '1 0' -m b

  $ hg status --rev tip --rev "tip^1"
  M a
  $ HGEDITOR=cat hg backout -d '2 0' tip --tool=true
  reverting a
  Backed out changeset a820f4f40a57
  
  
  HG: Enter commit message.  Lines beginning with 'HG:' are removed.
  HG: Leave message empty to abort commit.
  HG: --
  HG: user: test
  HG: branch 'default'
  HG: changed a
  changeset 2:2929462c3dff backs out changeset 1:a820f4f40a57
  $ cat a
  a
  $ hg summary
  parent: 2:2929462c3dff tip
   Backed out changeset a820f4f40a57
  branch: default
  commit: (clean)
  update: (current)
  phases: 3 draft

commit option

  $ cd ..
  $ hg init commit
  $ cd commit

  $ echo tomatoes > a
  $ hg add a
  $ hg commit -d '0 0' -m tomatoes

  $ echo chair > b
  $ hg add b
  $ hg commit -d '1 0' -m chair

  $ echo grapes >> a
  $ hg commit -d '2 0' -m grapes

  $ hg backout -d '4 0' 1 --tool=:fail
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  changeset 3:1c2161e97c0a backs out changeset 1:22cb4f70d813
  $ hg summary
  parent: 3:1c2161e97c0a tip
   Backed out changeset 22cb4f70d813
  branch: default
  commit: (clean)
  update: (current)
  phases: 4 draft

  $ echo ypples > a
  $ hg commit -d '5 0' -m ypples

  $ hg backout -d '6 0' 2 --tool=:fail
  0 files updated, 0 files merged, 0 files removed, 1 files unresolved
  use 'hg resolve' to retry unresolved file merges
  [1]
  $ hg summary
  parent: 4:ed99997b793d tip
   ypples
  branch: default
  commit: 1 unresolved (clean)
  update: (current)
  phases: 5 draft
  $ hg log -G
  @  changeset:   4:ed99997b793d
  |  tag:         tip
  |  user:        test
  |  date:        Thu Jan 01 00:00:05 1970 +0000
  |  summary:     ypples
  |
  o  changeset:   3:1c2161e97c0a
  |  user:        test
  |  date:        Thu Jan 01 00:00:04 1970 +0000
  |  summary:     Backed out changeset 22cb4f70d813
  |
  o  changeset:   2:a8c6e511cfee
  |  user:        test
  |  date:        Thu Jan 01 00:00:02 1970 +0000
  |  summary:     grapes
  |
  %  changeset:   1:22cb4f70d813
  |  user:        test
  |  date:        Thu Jan 01 00:00:01 1970 +0000
  |  summary:     chair
  |
  o  changeset:   0:a5cb2dde5805
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     tomatoes
  

file that was removed is recreated
(this also tests that editor is not invoked if the commit message is
specified explicitly)

  $ cd ..
  $ hg init remove
  $ cd remove

  $ echo content > a
  $ hg commit -d '0 0' -A -m a
  adding a

  $ hg rm a
  $ hg commit -d '1 0' -m b

  $ HGEDITOR=cat hg backout -d '2 0' tip --tool=true -m "Backed out changeset 76862dcce372"
  adding a
  changeset 2:de31bdc76c0d backs out changeset 1:76862dcce372
  $ cat a
  content
  $ hg summary
  parent: 2:de31bdc76c0d tip
   Backed out changeset 76862dcce372
  branch: default
  commit: (clean)
  update: (current)
  phases: 3 draft

backout of backout is as if nothing happened

  $ hg backout -d '3 0' --merge tip --tool=true
  removing a
  changeset 3:7f6d0f120113 backs out changeset 2:de31bdc76c0d
  $ test -f a
  [1]
  $ hg summary
  parent: 3:7f6d0f120113 tip
   Backed out changeset de31bdc76c0d
  branch: default
  commit: (clean)
  update: (current)
  phases: 4 draft

Test that 'hg rollback' restores dirstate just before opening
transaction: in-memory dirstate changes should be written into
'.hg/journal.dirstate' as expected.

  $ echo 'removed soon' > b
  $ hg commit -A -d '4 0' -m 'prepare for subsequent removing'
  adding b
  $ echo 'newly added' > c
  $ hg add c
  $ hg remove b
  $ hg commit -d '5 0' -m 'prepare for subsequent backout'
  $ touch -t 200001010000 c
  $ hg status -A
  C c
  $ hg debugstate --no-dates
  n 644         12 set                 c
  $ hg backout -d '6 0' -m 'to be rollback-ed soon' -r .
  removing c
  adding b
  changeset 6:4bfec048029d backs out changeset 5:fac0b729a654
  $ hg rollback -q
  $ hg status -A
  A b
  R c
  $ hg debugstate --no-dates
  a   0         -1 unset               b
  r   0          0 set                 c

across branch

  $ cd ..
  $ hg init branch
  $ cd branch
  $ echo a > a
  $ hg ci -Am0
  adding a
  $ echo b > b
  $ hg ci -Am1
  adding b
  $ hg co -C 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ hg summary
  parent: 0:f7b1eb17ad24 
   0
  branch: default
  commit: (clean)
  update: 1 new changesets (update)
  phases: 2 draft

should fail

  $ hg backout 1
  abort: cannot backout change that is not an ancestor
  [10]
  $ echo c > c
  $ hg ci -Am2
  adding c
  created new head
  $ hg summary
  parent: 2:db815d6d32e6 tip
   2
  branch: default
  commit: (clean)
  update: 1 new changesets, 2 branch heads (merge)
  phases: 3 draft

should fail

  $ hg backout 1
  abort: cannot backout change that is not an ancestor
  [10]
  $ hg summary
  parent: 2:db815d6d32e6 tip
   2
  branch: default
  commit: (clean)
  update: 1 new changesets, 2 branch heads (merge)
  phases: 3 draft

backout with merge

  $ cd ..
  $ hg init merge
  $ cd merge

  $ echo line 1 > a
  $ echo line 2 >> a
  $ hg commit -d '0 0' -A -m a
  adding a
  $ hg summary
  parent: 0:59395513a13a tip
   a
  branch: default
  commit: (clean)
  update: (current)
  phases: 1 draft

remove line 1

  $ echo line 2 > a
  $ hg commit -d '1 0' -m b

  $ echo line 3 >> a
  $ hg commit -d '2 0' -m c

  $ hg backout --merge -d '3 0' 1 --tool=true
  reverting a
  created new head
  changeset 3:26b8ccb9ad91 backs out changeset 1:5a50a024c182
  merging with changeset 3:26b8ccb9ad91
  merging a
  0 files updated, 1 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg commit -d '4 0' -m d
  $ hg summary
  parent: 4:c7df5e0b9c09 tip
   d
  branch: default
  commit: (clean)
  update: (current)
  phases: 5 draft

check line 1 is back

  $ cat a
  line 1
  line 2
  line 3

Test visibility of in-memory dirstate changes outside transaction to
external hook process

  $ cat > $TESTTMP/checkvisibility.sh <<EOF
  > echo "==== \$1:"
  > hg parents --template "{rev}:{node|short}\n"
  > echo "===="
  > EOF

"hg backout --merge REV1" at REV2 below implies steps below:

(1) update to REV1 (REV2 => REV1)
(2) revert by REV1^1
(3) commit backing out revision (REV3)
(4) update to REV2 (REV3 => REV2)
(5) merge with REV3 (REV2 => REV2, REV3)

== test visibility to external preupdate hook

  $ hg update -q -C 2
  $ hg --config extensions.strip= strip 3
  saved backup bundle to * (glob)

  $ cat >> .hg/hgrc <<EOF
  > [hooks]
  > preupdate.visibility = sh $TESTTMP/checkvisibility.sh preupdate
  > EOF

("-m" is needed to avoid writing dirstate changes out at other than
invocation of the hook to be examined)

  $ hg backout --merge -d '3 0' 1 --tool=true -m 'fixed comment'
  ==== preupdate:
  2:6ea3f2a197a2
  ====
  reverting a
  created new head
  changeset 3:d92a3f57f067 backs out changeset 1:5a50a024c182
  ==== preupdate:
  3:d92a3f57f067
  ====
  merging with changeset 3:d92a3f57f067
  ==== preupdate:
  2:6ea3f2a197a2
  ====
  merging a
  0 files updated, 1 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ cat >> .hg/hgrc <<EOF
  > [hooks]
  > preupdate.visibility =
  > EOF

== test visibility to external update hook

  $ hg update -q -C 2
  $ hg --config extensions.strip= strip 3
  saved backup bundle to * (glob)

  $ cat >> .hg/hgrc <<EOF
  > [hooks]
  > update.visibility = sh $TESTTMP/checkvisibility.sh update
  > EOF

  $ hg backout --merge -d '3 0' 1 --tool=true -m 'fixed comment'
  ==== update:
  1:5a50a024c182
  ====
  reverting a
  created new head
  changeset 3:d92a3f57f067 backs out changeset 1:5a50a024c182
  ==== update:
  2:6ea3f2a197a2
  ====
  merging with changeset 3:d92a3f57f067
  merging a
  ==== update:
  2:6ea3f2a197a2
  3:d92a3f57f067
  ====
  0 files updated, 1 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ cat >> .hg/hgrc <<EOF
  > [hooks]
  > update.visibility =
  > EOF

  $ cd ..

backout should not back out subsequent changesets

  $ hg init onecs
  $ cd onecs
  $ echo 1 > a
  $ hg commit -d '0 0' -A -m a
  adding a
  $ echo 2 >> a
  $ hg commit -d '1 0' -m b
  $ echo 1 > b
  $ hg commit -d '2 0' -A -m c
  adding b
  $ hg summary
  parent: 2:882396649954 tip
   c
  branch: default
  commit: (clean)
  update: (current)
  phases: 3 draft

without --merge
  $ hg backout --no-commit -d '3 0' 1 --tool=true
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  changeset 22bca4c721e5 backed out, don't forget to commit.
  $ hg locate b
  b
  $ hg update -C tip
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg locate b
  b
  $ hg summary
  parent: 2:882396649954 tip
   c
  branch: default
  commit: (clean)
  update: (current)
  phases: 3 draft

with --merge
  $ hg backout --merge -d '3 0' 1 --tool=true
  reverting a
  created new head
  changeset 3:3202beb76721 backs out changeset 1:22bca4c721e5
  merging with changeset 3:3202beb76721
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg locate b
  b
  $ hg update -C tip
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ hg locate b
  [1]

  $ cd ..
  $ hg init m
  $ cd m
  $ echo a > a
  $ hg commit -d '0 0' -A -m a
  adding a
  $ echo b > b
  $ hg commit -d '1 0' -A -m b
  adding b
  $ echo c > c
  $ hg commit -d '2 0' -A -m b
  adding c
  $ hg update 1
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ echo d > d
  $ hg commit -d '3 0' -A -m c
  adding d
  created new head
  $ hg merge 2
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg commit -d '4 0' -A -m d
  $ hg summary
  parent: 4:b2f3bb92043e tip
   d
  branch: default
  commit: (clean)
  update: (current)
  phases: 5 draft

backout of merge should fail

  $ hg backout 4
  abort: cannot backout a merge changeset
  [10]

backout of merge with bad parent should fail

  $ hg backout --parent 0 4
  abort: cb9a9f314b8b is not a parent of b2f3bb92043e
  [10]

backout of non-merge with parent should fail

  $ hg backout --parent 0 3
  abort: cannot use --parent on non-merge changeset
  [10]

backout with valid parent should be ok

  $ hg backout -d '5 0' --parent 2 4 --tool=true
  removing d
  changeset 5:10e5328c8435 backs out changeset 4:b2f3bb92043e
  $ hg summary
  parent: 5:10e5328c8435 tip
   Backed out changeset b2f3bb92043e
  branch: default
  commit: (clean)
  update: (current)
  phases: 6 draft

  $ hg rollback
  repository tip rolled back to revision 4 (undo commit)
  working directory now based on revision 4
  $ hg update -C
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg summary
  parent: 4:b2f3bb92043e tip
   d
  branch: default
  commit: (clean)
  update: (current)
  phases: 5 draft

  $ hg backout -d '6 0' --parent 3 4 --tool=true
  removing c
  changeset 5:033590168430 backs out changeset 4:b2f3bb92043e
  $ hg summary
  parent: 5:033590168430 tip
   Backed out changeset b2f3bb92043e
  branch: default
  commit: (clean)
  update: (current)
  phases: 6 draft

  $ cd ..

named branches

  $ hg init named_branches
  $ cd named_branches

  $ echo default > default
  $ hg ci -d '0 0' -Am default
  adding default
  $ hg branch branch1
  marked working directory as branch branch1
  (branches are permanent and global, did you want a bookmark?)
  $ echo branch1 > file1
  $ hg ci -d '1 0' -Am file1
  adding file1
  $ hg branch branch2
  marked working directory as branch branch2
  $ echo branch2 > file2
  $ hg ci -d '2 0' -Am file2
  adding file2

without --merge
  $ hg backout --no-commit -r 1 --tool=true
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  changeset bf1602f437f3 backed out, don't forget to commit.
  $ hg branch
  branch2
  $ hg status -A
  R file1
  C default
  C file2
  $ hg summary
  parent: 2:45bbcd363bf0 tip
   file2
  branch: branch2
  commit: 1 removed
  update: (current)
  phases: 3 draft

with --merge
(this also tests that editor is invoked if '--edit' is specified
explicitly regardless of '--message')

  $ hg update -qC
  $ HGEDITOR=cat hg backout --merge -d '3 0' -r 1 -m 'backout on branch1' --tool=true --edit
  removing file1
  backout on branch1
  
  
  HG: Enter commit message.  Lines beginning with 'HG:' are removed.
  HG: Leave message empty to abort commit.
  HG: --
  HG: user: test
  HG: branch 'branch2'
  HG: removed file1
  created new head
  changeset 3:d4e8f6db59fb backs out changeset 1:bf1602f437f3
  merging with changeset 3:d4e8f6db59fb
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg summary
  parent: 2:45bbcd363bf0 
   file2
  parent: 3:d4e8f6db59fb tip
   backout on branch1
  branch: branch2
  commit: 1 removed (merge)
  update: (current)
  phases: 4 draft
  $ hg update -q -C 2

on branch2 with branch1 not merged, so file1 should still exist:

  $ hg id
  45bbcd363bf0 (branch2)
  $ hg st -A
  C default
  C file1
  C file2
  $ hg summary
  parent: 2:45bbcd363bf0 
   file2
  branch: branch2
  commit: (clean)
  update: 1 new changesets, 2 branch heads (merge)
  phases: 4 draft

on branch2 with branch1 merged, so file1 should be gone:

  $ hg merge
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -d '4 0' -m 'merge backout of branch1'
  $ hg id
  d97a8500a969 (branch2) tip
  $ hg st -A
  C default
  C file2
  $ hg summary
  parent: 4:d97a8500a969 tip
   merge backout of branch1
  branch: branch2
  commit: (clean)
  update: (current)
  phases: 5 draft

on branch1, so no file1 and file2:

  $ hg co -C branch1
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ hg id
  bf1602f437f3 (branch1)
  $ hg st -A
  C default
  C file1
  $ hg summary
  parent: 1:bf1602f437f3 
   file1
  branch: branch1
  commit: (clean)
  update: (current)
  phases: 5 draft

  $ cd ..

backout of empty changeset (issue4190)

  $ hg init emptycommit
  $ cd emptycommit

  $ touch file1
  $ hg ci -Aqm file1
  $ hg branch -q branch1
  $ hg ci -qm branch1
  $ hg backout -v 1
  resolving manifests
  nothing changed
  [1]

  $ cd ..


Test usage of `hg resolve` in case of conflict
(issue4163)

  $ hg init issue4163
  $ cd issue4163
  $ touch foo
  $ hg add foo
  $ cat > foo << EOF
  > one
  > two
  > three
  > four
  > five
  > six
  > seven
  > height
  > nine
  > ten
  > EOF
  $ hg ci -m 'initial'
  $ cat > foo << EOF
  > one
  > two
  > THREE
  > four
  > five
  > six
  > seven
  > height
  > nine
  > ten
  > EOF
  $ hg ci -m 'capital three'
  $ cat > foo << EOF
  > one
  > two
  > THREE
  > four
  > five
  > six
  > seven
  > height
  > nine
  > TEN
  > EOF
  $ hg ci -m 'capital ten'
  $ hg backout -r 'desc("capital three")' --tool internal:fail
  0 files updated, 0 files merged, 0 files removed, 1 files unresolved
  use 'hg resolve' to retry unresolved file merges
  [1]
  $ hg status
  $ hg debugmergestate -v
  v1 and v2 states match: using v2
  local: b71750c4b0fdf719734971e3ef90dbeab5919a2d
  other: a30dd8addae3ce71b8667868478542bc417439e6
  file: foo (state "u")
    local path: foo (hash 0beec7b5ea3f0fdbc95d0dd47f3c5bc275da8a33, flags "")
    ancestor path: foo (node f89532f44c247a0e993d63e3a734dd781ab04708)
    other path: foo (node f50039b486d6fa1a90ae51778388cad161f425ee)
    extra: ancestorlinknode = 91360952243723bd5b1138d5f26bd8c8564cb553
    extra: merged = yes
  $ mv .hg/merge/state2 .hg/merge/state2-moved
  $ hg debugmergestate -v
  no version 2 merge state
  local: b71750c4b0fdf719734971e3ef90dbeab5919a2d
  other: b71750c4b0fdf719734971e3ef90dbeab5919a2d
  file: foo (state "u")
    local path: foo (hash 0beec7b5ea3f0fdbc95d0dd47f3c5bc275da8a33, flags "")
    ancestor path: foo (node f89532f44c247a0e993d63e3a734dd781ab04708)
    other path:  (node foo)
  $ mv .hg/merge/state2-moved .hg/merge/state2
  $ hg resolve -l  # still unresolved
  U foo
  $ hg summary
  parent: 2:b71750c4b0fd tip
   capital ten
  branch: default
  commit: 1 unresolved (clean)
  update: (current)
  phases: 3 draft
  $ hg log -G
  @  changeset:   2:b71750c4b0fd
  |  tag:         tip
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     capital ten
  |
  o  changeset:   1:913609522437
  |  user:        test
  |  date:        Thu Jan 01 00:00:00 1970 +0000
  |  summary:     capital three
  |
  %  changeset:   0:a30dd8addae3
     user:        test
     date:        Thu Jan 01 00:00:00 1970 +0000
     summary:     initial
  
  $ hg resolve --all --debug
  picked tool ':merge' for foo (binary False symlink False changedelete False)
  merging foo
  my foo@b71750c4b0fd+ other foo@a30dd8addae3 ancestor foo@913609522437
   premerge successful
  (no more unresolved files)
  continue: hg commit
  $ hg status
  M foo
  ? foo.orig
  $ hg resolve -l
  R foo
  $ hg summary
  parent: 2:b71750c4b0fd tip
   capital ten
  branch: default
  commit: 1 modified, 1 unknown
  update: (current)
  phases: 3 draft
  $ cat foo
  one
  two
  three
  four
  five
  six
  seven
  height
  nine
  TEN

--no-commit shouldn't commit

  $ hg init a
  $ cd a
  $ for i in 1 2 3; do
  >   touch $i
  >   hg ci -Am $i
  > done
  adding 1
  adding 2
  adding 3
  $ hg backout --no-commit .
  removing 3
  changeset cccc23d9d68f backed out, don't forget to commit.
  $ hg revert -aq

--no-commit can't be used with --merge

  $ hg backout --merge --no-commit 2
  abort: cannot specify both --no-commit and --merge
  [10]

Ensure that backout out the same changeset twice performs correctly:

  $ hg backout 2
  removing 3
  changeset 3:8f188de730d9 backs out changeset 2:cccc23d9d68f
  $ echo 4 > 4
  $ hg ci -A -m 4
  adding 4
  $ hg up 2
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ hg backout 2
  removing 3
  warning: commit already existed in the repository!
  changeset 3:8f188de730d9 backs out changeset 2:cccc23d9d68f