view tests/test-rebase-collapse.t @ 35569:964212780daf

rust: implementation of `hg`

This commit provides a mostly-working implementation of the
`hg` script in Rust along with scaffolding to support Rust in
the repository.

If you are familiar with Rust, the contents of the added rust/
directory should be pretty straightforward. We create an "hgcli"
package that implements a binary application to run Mercurial.
The output of this package is an "hg" binary.

Our Rust `hg` (henceforth "rhg") essentially is a port of the existing
`hg` Python script. The main difference is the creation of the embedded
CPython interpreter is handled by the binary itself instead of relying
on the shebang. In that sense, rhg is more similar to the "exe wrapper"
we currently use on Windows. However, unlike the exe wrapper, rhg does
not call the `hg` Python script. Instead, it uses the CPython APIs to
import mercurial modules and call appropriate functions. The amount of
code here is surprisingly small.

It is my intent to replace the existing C-based exe wrapper with rhg.
Preferably in the next Mercurial release. This should be achievable -
at least for some Mercurial distributions. The future/timeline for
rhg on other platforms is less clear. We already ship a hg.exe on
Windows. So if we get the quirks with Rust worked out, shipping a
Rust-based hg.exe should hopefully not be too contentious.

Now onto the implementation.

We're using python27-sys and the cpython crates for talking to the
CPython API. We currently don't use too much functionality of the
cpython crate and could have probably cut it out. However, it does
provide a reasonable abstraction over unsafe {} CPython function
calls. While we still have our fair share of those, at least we're
not dealing with too much refcounting, error checking, etc. So I
think the use of the cpython crate is justified. Plus, there is
not-yet-implemented functionality that could benefit from cpython. I
see our use of this crate only increasing.

The cpython and python27-sys crates are not without their issues.
The cpython crate didn't seem to account for the embedding use case
in its design. Instead, it seems to assume that you are building
a Python extension. It is making some questionable decisions around
certain CPython APIs. For example, it insists that
PyEval_ThreadsInitialized() is called and that the Python code
likely isn't the main thread in the underlying application. It
is also missing some functionality that is important for embedded
use cases (such as exporting the path to the Python interpreter
from its build script). After spending several hours trying to
wrangle python27-sys and cpython, I gave up and forked the project
on GitHub. Our Cargo.toml tracks this fork. I'm optimistic that
the upstream project will accept our contributions and we can
eventually unfork.

There is a non-trivial amount of code in our custom Cargo build
script. Our build.rs (which is called as part of building the hgcli
crate):

* Validates that the Python interpreter that was detected by the
  python27-sys crate provides a shared library (we only support
  shared library linking at this time - although this restriction
  could be loosened).
* Validates that the Python is built with UCS-4 support. This ensures
  maximum Unicode compatibility.
* Exports variables to the crate build allowing the built crate to e.g.
  find the path to the Python interpreter.

The produced rhg should be considered alpha quality. There are several
known deficiencies. Many of these are documented with inline TODOs.

Probably the biggest limitation of rhg is that it assumes it is
running from the ./rust/target/<target> directory of a source
distribution. So, rhg is currently not very practical for real-world
use. But, if you can `cargo build` it, running the binary *should*
yield a working Mercurial CLI.

In order to support using rhg with the test harness, we needed to hack
up run-tests.py so the path to Mercurial's Python files is set properly.
The change is extremely hacky and is only intended to be a stop-gap
until the test harness gains first-class support for installing rhg.
This will likely occur after we support running rhg outside the
source directory.

Despite its officially alpha quality, rhg copes extremely well with
the test harness (at least on Linux). Using
`run-tests.py --with-hg ../rust/target/debug/hg`, I only encounter
the following failures:

* test-run-tests.t -- Warnings emitted about using an unexpected
  Mercurial library. This is due to the hacky nature of setting the
  Python directory when run-tests.py detected rhg.
* test-devel-warnings.t -- Expected stack trace missing frame for `hg`
  (This is expected since we no longer have an `hg` script!)
* test-convert.t -- Test running `$PYTHON "$BINDIR"/hg`, which obviously
  assumes `hg` is a Python script.
* test-merge-tools.t -- Same assumption about `hg` being executable with
  Python.
* test-http-bad-server.t -- Seeing exit code 255 instead of 1 around
  line 358.
* test-blackbox.t -- Exit code 255 instead of 1.
* test-basic.t -- Exit code 255 instead of 1.

It certainly looks like we have a bug around exit code handling. I
don't think it is severe enough to hold up review and landing of this
initial implementation. Perfect is the enemy of good.

Differential Revision: https://phab.mercurial-scm.org/D1581

  $ cat >> $HGRCPATH <<EOF
  > [extensions]
  > rebase=
  > mq=
  > 
  > [phases]
  > publish=False
  > 
  > [alias]
  > tglog = log -G --template "{rev}: {node|short} '{desc}' {branches}\n"
  > tglogp = log -G --template "{rev}: {node|short} {phase} '{desc}' {branches}\n"
  > EOF

Create repo a:

  $ hg init a
  $ cd a
  $ hg unbundle "$TESTDIR/bundles/rebase.hg"
  adding changesets
  adding manifests
  adding file changes
  added 8 changesets with 7 changes to 7 files (+2 heads)
  new changesets cd010b8cd998:02de42196ebe
  (run 'hg heads' to see heads, 'hg merge' to merge)
  $ hg up tip
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ hg tglog
  @  7: 02de42196ebe 'H'
  |
  | o  6: eea13746799a 'G'
  |/|
  o |  5: 24b6387c8c8c 'F'
  | |
  | o  4: 9520eea781bc 'E'
  |/
  | o  3: 32af7686d403 'D'
  | |
  | o  2: 5fddd98957c8 'C'
  | |
  | o  1: 42ccdea3bb16 'B'
  |/
  o  0: cd010b8cd998 'A'
  
  $ cd ..


Rebasing B onto H and collapsing changesets with different phases:


  $ hg clone -q -u 3 a a1
  $ cd a1

  $ hg phase --force --secret 3

  $ cat > $TESTTMP/editor.sh <<EOF
  > echo "==== before editing"
  > cat \$1
  > echo "===="
  > echo "edited manually" >> \$1
  > EOF
  $ HGEDITOR="sh $TESTTMP/editor.sh" hg rebase --collapse --keepbranches -e --dest 7
  rebasing 1:42ccdea3bb16 "B"
  rebasing 2:5fddd98957c8 "C"
  rebasing 3:32af7686d403 "D"
  ==== before editing
  Collapsed revision
  * B
  * C
  * D
  
  
  HG: Enter commit message.  Lines beginning with 'HG:' are removed.
  HG: Leave message empty to abort commit.
  HG: --
  HG: user: Nicolas Dumazet <[e-mail]>
  HG: branch 'default'
  HG: added B
  HG: added C
  HG: added D
  ====
  saved backup bundle to $TESTTMP/a1/.hg/strip-backup/42ccdea3bb16-3cb021d3-rebase.hg

  $ hg tglogp
  @  5: 30882080ba93 secret 'Collapsed revision
  |  * B
  |  * C
  |  * D
  |
  |
  |  edited manually'
  o  4: 02de42196ebe draft 'H'
  |
  | o  3: eea13746799a draft 'G'
  |/|
  o |  2: 24b6387c8c8c draft 'F'
  | |
  | o  1: 9520eea781bc draft 'E'
  |/
  o  0: cd010b8cd998 draft 'A'
  
  $ hg manifest --rev tip
  A
  B
  C
  D
  F
  H

  $ cd ..


Rebasing E onto H:

  $ hg clone -q -u . a a2
  $ cd a2

  $ hg phase --force --secret 6
  $ hg rebase --source 4 --collapse --dest 7
  rebasing 4:9520eea781bc "E"
  rebasing 6:eea13746799a "G"
  saved backup bundle to $TESTTMP/a2/.hg/strip-backup/9520eea781bc-fcd8edd4-rebase.hg

  $ hg tglog
  o  6: 7dd333a2d1e4 'Collapsed revision
  |  * E
  |  * G'
  @  5: 02de42196ebe 'H'
  |
  o  4: 24b6387c8c8c 'F'
  |
  | o  3: 32af7686d403 'D'
  | |
  | o  2: 5fddd98957c8 'C'
  | |
  | o  1: 42ccdea3bb16 'B'
  |/
  o  0: cd010b8cd998 'A'
  
  $ hg manifest --rev tip
  A
  E
  F
  H

  $ cd ..

Rebasing G onto H with custom message:

  $ hg clone -q -u . a a3
  $ cd a3

  $ hg rebase --base 6 -m 'custom message'
  abort: message can only be specified with collapse
  [255]

  $ cat > $TESTTMP/checkeditform.sh <<EOF
  > env | grep HGEDITFORM
  > true
  > EOF
  $ HGEDITOR="sh $TESTTMP/checkeditform.sh" hg rebase --source 4 --collapse -m 'custom message' -e --dest 7
  rebasing 4:9520eea781bc "E"
  rebasing 6:eea13746799a "G"
  HGEDITFORM=rebase.collapse
  saved backup bundle to $TESTTMP/a3/.hg/strip-backup/9520eea781bc-fcd8edd4-rebase.hg

  $ hg tglog
  o  6: 38ed6a6b026b 'custom message'
  |
  @  5: 02de42196ebe 'H'
  |
  o  4: 24b6387c8c8c 'F'
  |
  | o  3: 32af7686d403 'D'
  | |
  | o  2: 5fddd98957c8 'C'
  | |
  | o  1: 42ccdea3bb16 'B'
  |/
  o  0: cd010b8cd998 'A'
  
  $ hg manifest --rev tip
  A
  E
  F
  H

  $ cd ..

Create repo b:

  $ hg init b
  $ cd b

  $ echo A > A
  $ hg ci -Am A
  adding A
  $ echo B > B
  $ hg ci -Am B
  adding B

  $ hg up -q 0

  $ echo C > C
  $ hg ci -Am C
  adding C
  created new head

  $ hg merge
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ echo D > D
  $ hg ci -Am D
  adding D

  $ hg up -q 1

  $ echo E > E
  $ hg ci -Am E
  adding E
  created new head

  $ echo F > F
  $ hg ci -Am F
  adding F

  $ hg merge
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -m G

  $ hg up -q 0

  $ echo H > H
  $ hg ci -Am H
  adding H
  created new head

  $ hg tglog
  @  7: c65502d41787 'H'
  |
  | o    6: c772a8b2dc17 'G'
  | |\
  | | o  5: 7f219660301f 'F'
  | | |
  | | o  4: 8a5212ebc852 'E'
  | | |
  | o |  3: 2870ad076e54 'D'
  | |\|
  | o |  2: c5cefa58fd55 'C'
  |/ /
  | o  1: 27547f69f254 'B'
  |/
  o  0: 4a2df7238c3b 'A'
  
  $ cd ..


Rebase and collapse - more than one external (fail):

  $ hg clone -q -u . b b1
  $ cd b1

  $ hg rebase -s 2 --dest 7 --collapse
  abort: unable to collapse on top of 7, there is more than one external parent: 1, 5
  [255]

Rebase and collapse - E onto H:

  $ hg rebase -s 4 --dest 7 --collapse # root (4) is not a merge
  rebasing 4:8a5212ebc852 "E"
  rebasing 5:7f219660301f "F"
  rebasing 6:c772a8b2dc17 "G"
  saved backup bundle to $TESTTMP/b1/.hg/strip-backup/8a5212ebc852-75046b61-rebase.hg

  $ hg tglog
  o    5: f97c4725bd99 'Collapsed revision
  |\   * E
  | |  * F
  | |  * G'
  | @  4: c65502d41787 'H'
  | |
  o |    3: 2870ad076e54 'D'
  |\ \
  | o |  2: c5cefa58fd55 'C'
  | |/
  o /  1: 27547f69f254 'B'
  |/
  o  0: 4a2df7238c3b 'A'
  
  $ hg manifest --rev tip
  A
  C
  D
  E
  F
  H

  $ cd ..




Test that branchheads cache is updated correctly when doing a strip in which
the parent of the ancestor node to be stripped does not become a head and also,
the parent of a node that is a child of the node stripped becomes a head (node
3). The code is now much simpler and we could just test a simpler scenario
We keep it the test this way in case new complexity is injected.

  $ hg clone -q -u . b b2
  $ cd b2

  $ hg heads --template="{rev}:{node} {branch}\n"
  7:c65502d4178782309ce0574c5ae6ee9485a9bafa default
  6:c772a8b2dc17629cec88a19d09c926c4814b12c7 default

  $ cat $TESTTMP/b2/.hg/cache/branch2-served
  c65502d4178782309ce0574c5ae6ee9485a9bafa 7
  c772a8b2dc17629cec88a19d09c926c4814b12c7 o default
  c65502d4178782309ce0574c5ae6ee9485a9bafa o default

  $ hg strip 4
  saved backup bundle to $TESTTMP/b2/.hg/strip-backup/8a5212ebc852-75046b61-backup.hg

  $ cat $TESTTMP/b2/.hg/cache/branch2-served
  c65502d4178782309ce0574c5ae6ee9485a9bafa 4
  2870ad076e541e714f3c2bc32826b5c6a6e5b040 o default
  c65502d4178782309ce0574c5ae6ee9485a9bafa o default

  $ hg heads --template="{rev}:{node} {branch}\n"
  4:c65502d4178782309ce0574c5ae6ee9485a9bafa default
  3:2870ad076e541e714f3c2bc32826b5c6a6e5b040 default

  $ cd ..






Create repo c:

  $ hg init c
  $ cd c

  $ echo A > A
  $ hg ci -Am A
  adding A
  $ echo B > B
  $ hg ci -Am B
  adding B

  $ hg up -q 0

  $ echo C > C
  $ hg ci -Am C
  adding C
  created new head

  $ hg merge
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ echo D > D
  $ hg ci -Am D
  adding D

  $ hg up -q 1

  $ echo E > E
  $ hg ci -Am E
  adding E
  created new head
  $ echo F > E
  $ hg ci -m 'F'

  $ echo G > G
  $ hg ci -Am G
  adding G

  $ hg merge
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ hg ci -m H

  $ hg up -q 0

  $ echo I > I
  $ hg ci -Am I
  adding I
  created new head

  $ hg tglog
  @  8: 46d6f0e29c20 'I'
  |
  | o    7: 417d3b648079 'H'
  | |\
  | | o  6: 55a44ad28289 'G'
  | | |
  | | o  5: dca5924bb570 'F'
  | | |
  | | o  4: 8a5212ebc852 'E'
  | | |
  | o |  3: 2870ad076e54 'D'
  | |\|
  | o |  2: c5cefa58fd55 'C'
  |/ /
  | o  1: 27547f69f254 'B'
  |/
  o  0: 4a2df7238c3b 'A'
  
  $ cd ..


Rebase and collapse - E onto I:

  $ hg clone -q -u . c c1
  $ cd c1

  $ hg rebase -s 4 --dest 8 --collapse # root (4) is not a merge
  rebasing 4:8a5212ebc852 "E"
  rebasing 5:dca5924bb570 "F"
  merging E
  rebasing 6:55a44ad28289 "G"
  rebasing 7:417d3b648079 "H"
  saved backup bundle to $TESTTMP/c1/.hg/strip-backup/8a5212ebc852-f95d0879-rebase.hg

  $ hg tglog
  o    5: 340b34a63b39 'Collapsed revision
  |\   * E
  | |  * F
  | |  * G
  | |  * H'
  | @  4: 46d6f0e29c20 'I'
  | |
  o |    3: 2870ad076e54 'D'
  |\ \
  | o |  2: c5cefa58fd55 'C'
  | |/
  o /  1: 27547f69f254 'B'
  |/
  o  0: 4a2df7238c3b 'A'
  
  $ hg manifest --rev tip
  A
  C
  D
  E
  G
  I

  $ hg up tip -q
  $ cat E
  F

  $ cd ..


Create repo d:

  $ hg init d
  $ cd d

  $ echo A > A
  $ hg ci -Am A
  adding A
  $ echo B > B
  $ hg ci -Am B
  adding B
  $ echo C > C
  $ hg ci -Am C
  adding C

  $ hg up -q 1

  $ echo D > D
  $ hg ci -Am D
  adding D
  created new head
  $ hg merge
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

  $ hg ci -m E

  $ hg up -q 0

  $ echo F > F
  $ hg ci -Am F
  adding F
  created new head

  $ hg tglog
  @  5: c137c2b8081f 'F'
  |
  | o    4: 0a42590ed746 'E'
  | |\
  | | o  3: 7bbcd6078bcc 'D'
  | | |
  | o |  2: f838bfaca5c7 'C'
  | |/
  | o  1: 27547f69f254 'B'
  |/
  o  0: 4a2df7238c3b 'A'
  
  $ cd ..


Rebase and collapse - B onto F:

  $ hg clone -q -u . d d1
  $ cd d1

  $ hg rebase -s 1 --collapse --dest 5
  rebasing 1:27547f69f254 "B"
  rebasing 2:f838bfaca5c7 "C"
  rebasing 3:7bbcd6078bcc "D"
  rebasing 4:0a42590ed746 "E"
  saved backup bundle to $TESTTMP/d1/.hg/strip-backup/27547f69f254-9a3f7d92-rebase.hg

  $ hg tglog
  o  2: b72eaccb283f 'Collapsed revision
  |  * B
  |  * C
  |  * D
  |  * E'
  @  1: c137c2b8081f 'F'
  |
  o  0: 4a2df7238c3b 'A'
  
  $ hg manifest --rev tip
  A
  B
  C
  D
  F

Interactions between collapse and keepbranches
  $ cd ..
  $ hg init e
  $ cd e
  $ echo 'a' > a
  $ hg ci -Am 'A'
  adding a

  $ hg branch 'one'
  marked working directory as branch one
  (branches are permanent and global, did you want a bookmark?)
  $ echo 'b' > b
  $ hg ci -Am 'B'
  adding b

  $ hg branch 'two'
  marked working directory as branch two
  $ echo 'c' > c
  $ hg ci -Am 'C'
  adding c

  $ hg up -q 0
  $ echo 'd' > d
  $ hg ci -Am 'D'
  adding d

  $ hg tglog
  @  3: 41acb9dca9eb 'D'
  |
  | o  2: 8ac4a08debf1 'C' two
  | |
  | o  1: 1ba175478953 'B' one
  |/
  o  0: 1994f17a630e 'A'
  
  $ hg rebase --keepbranches --collapse -s 1 -d 3
  abort: cannot collapse multiple named branches
  [255]

  $ repeatchange() {
  >   hg checkout $1
  >   hg cp d z
  >   echo blah >> z
  >   hg commit -Am "$2" --user "$3"
  > }
  $ repeatchange 3 "E" "user1"
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ repeatchange 3 "E" "user2"
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  created new head
  $ hg tglog
  @  5: fbfb97b1089a 'E'
  |
  | o  4: f338eb3c2c7c 'E'
  |/
  o  3: 41acb9dca9eb 'D'
  |
  | o  2: 8ac4a08debf1 'C' two
  | |
  | o  1: 1ba175478953 'B' one
  |/
  o  0: 1994f17a630e 'A'
  
  $ hg rebase -s 5 -d 4
  rebasing 5:fbfb97b1089a "E" (tip)
  note: rebase of 5:fbfb97b1089a created no changes to commit
  saved backup bundle to $TESTTMP/e/.hg/strip-backup/fbfb97b1089a-553e1d85-rebase.hg
  $ hg tglog
  @  4: f338eb3c2c7c 'E'
  |
  o  3: 41acb9dca9eb 'D'
  |
  | o  2: 8ac4a08debf1 'C' two
  | |
  | o  1: 1ba175478953 'B' one
  |/
  o  0: 1994f17a630e 'A'
  
  $ hg export tip
  # HG changeset patch
  # User user1
  # Date 0 0
  #      Thu Jan 01 00:00:00 1970 +0000
  # Node ID f338eb3c2c7cc5b5915676a2376ba7ac558c5213
  # Parent  41acb9dca9eb976e84cd21fcb756b4afa5a35c09
  E
  
  diff -r 41acb9dca9eb -r f338eb3c2c7c z
  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
  +++ b/z	Thu Jan 01 00:00:00 1970 +0000
  @@ -0,0 +1,2 @@
  +d
  +blah

  $ cd ..

Rebase, collapse and copies

  $ hg init copies
  $ cd copies
  $ hg unbundle "$TESTDIR/bundles/renames.hg"
  adding changesets
  adding manifests
  adding file changes
  added 4 changesets with 11 changes to 7 files (+1 heads)
  new changesets f447d5abf5ea:338e84e2e558
  (run 'hg heads' to see heads, 'hg merge' to merge)
  $ hg up -q tip
  $ hg tglog
  @  3: 338e84e2e558 'move2'
  |
  o  2: 6e7340ee38c0 'move1'
  |
  | o  1: 1352765a01d4 'change'
  |/
  o  0: f447d5abf5ea 'add'
  
  $ hg rebase --collapse -d 1
  rebasing 2:6e7340ee38c0 "move1"
  merging a and d to d
  merging b and e to e
  merging c and f to f
  rebasing 3:338e84e2e558 "move2" (tip)
  merging f and c to c
  merging e and g to g
  saved backup bundle to $TESTTMP/copies/.hg/strip-backup/6e7340ee38c0-ef8ef003-rebase.hg
  $ hg st
  $ hg st --copies --change tip
  A d
    a
  A g
    b
  R b
  $ hg up tip -q
  $ cat c
  c
  c
  $ cat d
  a
  a
  $ cat g
  b
  b
  $ hg log -r . --template "{file_copies}\n"
  d (a)g (b)

Test collapsing a middle revision in-place

  $ hg tglog
  @  2: 64b456429f67 'Collapsed revision
  |  * move1
  |  * move2'
  o  1: 1352765a01d4 'change'
  |
  o  0: f447d5abf5ea 'add'
  
  $ hg rebase --collapse -r 1 -d 0
  abort: can't remove original changesets with unrebased descendants
  (use --keep to keep original changesets)
  [255]

Test collapsing in place

  $ hg rebase --collapse -b . -d 0
  rebasing 1:1352765a01d4 "change"
  rebasing 2:64b456429f67 "Collapsed revision" (tip)
  saved backup bundle to $TESTTMP/copies/.hg/strip-backup/1352765a01d4-45a352ea-rebase.hg
  $ hg st --change tip --copies
  M a
  M c
  A d
    a
  A g
    b
  R b
  $ hg up tip -q
  $ cat a
  a
  a
  $ cat c
  c
  c
  $ cat d
  a
  a
  $ cat g
  b
  b
  $ cd ..


Test stripping a revision with another child

  $ hg init f
  $ cd f

  $ echo A > A
  $ hg ci -Am A
  adding A
  $ echo B > B
  $ hg ci -Am B
  adding B

  $ hg up -q 0

  $ echo C > C
  $ hg ci -Am C
  adding C
  created new head

  $ hg tglog
  @  2: c5cefa58fd55 'C'
  |
  | o  1: 27547f69f254 'B'
  |/
  o  0: 4a2df7238c3b 'A'
  


  $ hg heads --template="{rev}:{node} {branch}: {desc}\n"
  2:c5cefa58fd557f84b72b87f970135984337acbc5 default: C
  1:27547f69f25460a52fff66ad004e58da7ad3fb56 default: B

  $ hg strip 2
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  saved backup bundle to $TESTTMP/f/.hg/strip-backup/c5cefa58fd55-629429f4-backup.hg

  $ hg tglog
  o  1: 27547f69f254 'B'
  |
  @  0: 4a2df7238c3b 'A'
  


  $ hg heads --template="{rev}:{node} {branch}: {desc}\n"
  1:27547f69f25460a52fff66ad004e58da7ad3fb56 default: B

  $ cd ..

Test collapsing changes that add then remove a file

  $ hg init collapseaddremove
  $ cd collapseaddremove

  $ touch base
  $ hg commit -Am base
  adding base
  $ touch a
  $ hg commit -Am a
  adding a
  $ hg rm a
  $ touch b
  $ hg commit -Am b
  adding b
  $ hg book foo
  $ hg rebase -d 0 -r "1::2" --collapse -m collapsed
  rebasing 1:6d8d9f24eec3 "a"
  rebasing 2:1cc73eca5ecc "b" (foo tip)
  saved backup bundle to $TESTTMP/collapseaddremove/.hg/strip-backup/6d8d9f24eec3-77d3b6e2-rebase.hg
  $ hg log -G --template "{rev}: '{desc}' {bookmarks}"
  @  1: 'collapsed' foo
  |
  o  0: 'base'
  
  $ hg manifest --rev tip
  b
  base

  $ cd ..

Test that rebase --collapse will remember message after
running into merge conflict and invoking rebase --continue.

  $ hg init collapse_remember_message
  $ cd collapse_remember_message
  $ touch a
  $ hg add a
  $ hg commit -m "a"
  $ echo "a-default" > a
  $ hg commit -m "a-default"
  $ hg update -r 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg branch dev
  marked working directory as branch dev
  (branches are permanent and global, did you want a bookmark?)
  $ echo "a-dev" > a
  $ hg commit -m "a-dev"
  $ hg rebase --collapse -m "a-default-dev" -d 1
  rebasing 2:b8d8db2b242d "a-dev" (tip)
  merging a
  warning: conflicts while merging a! (edit, then use 'hg resolve --mark')
  unresolved conflicts (see hg resolve, then hg rebase --continue)
  [1]
  $ rm a.orig
  $ hg resolve --mark a
  (no more unresolved files)
  continue: hg rebase --continue
  $ hg rebase --continue
  rebasing 2:b8d8db2b242d "a-dev" (tip)
  saved backup bundle to $TESTTMP/collapse_remember_message/.hg/strip-backup/b8d8db2b242d-f474c19a-rebase.hg
  $ hg log
  changeset:   2:45ba1d1a8665
  tag:         tip
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     a-default-dev
  
  changeset:   1:3c8db56a44bc
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     a-default
  
  changeset:   0:3903775176ed
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     a
  
  $ cd ..