view tests/test-copytrace-heuristics.t @ 35884:197d10e157ce

httppeer: remove support for connecting to <0.9.1 servers (BC)

Previously, HTTP wire protocol clients would attempt a
"capabilities" wire protocol command. If that failed, they would
fall back to issuing a "between" command.

The "capabilities" command was added in Mercurial 0.9.1 (released
July 2006). The "between" command has been present for as long as
the wire protocol has existed. So if the "between" command failed,
it was safe to assume that the remote could not speak any version
of the Mercurial wire protocol.

The "between" fallback was added in 395a84f78736 in 2011. Before that
changeset, Mercurial would *always* issue the "between" command and
would issue "capabilities" if capabilities were requested. At that time,
many connections would issue "capabilities" eventually, so it was
decided to issue "capabilities" by default and fall back to "between"
if that failed. This saved a round trip when connecting to modern
servers while still preserving compatibility with legacy servers.

Fast forward ~7 years. Mercurial servers supporting "capabilities"
have been around for over a decade. If modern clients are
connecting to <0.9.1 servers, they are getting a bad experience.
They may even be getting bad data (an old server is vulnerable to
numerous security issues and could have been p0wned, leading to a
Mercurial repository serving backdoors or other badness).

In addition, the fallback can harm experience for modern servers.
If a client experiences an intermittent HTTP request failure (due to
bad network, etc) and falls back to a "between" that works, it would
assume an empty capability set and would attempt to communicate with
the repository using a very ancient wire protocol. Auditing HTTP logs
for hg.mozilla.org, I did find a handful of requests for the
null range of the "between" command. However, requests can be days
apart. And when I do see requests, they come in batches. Those
batches seem to correlate to spikes of HTTP 500 or other
server/network events. So I think these requests are fallbacks from
failed "capabilities" requests and not from old clients.

If you need even more evidence to discontinue support, apparently
we have no test coverage for communicating with servers not
supporting "capabilities." I know this because all tests pass
with the "between" fallback removed.

Finally, server-side support for <0.9.1 pushing (the "addchangegroup"
wire protocol command along with locking-related commands) was dropped
from the HTTP client in fda0867cfe03 in 2017 and the SSH client in
9f6e0e7ef828 in 2015.

I think this all adds up to enough justification for removing client
support for communicating with servers not supporting "capabilities."
So this commit removes that fallback.

Differential Revision: https://phab.mercurial-scm.org/D2001

Test for the heuristic copytracing algorithm
============================================

  $ cat >> $TESTTMP/copytrace.sh << '__EOF__'
  > initclient() {
  > cat >> $1/.hg/hgrc <<EOF
  > [experimental]
  > copytrace = heuristics
  > copytrace.sourcecommitlimit = -1
  > EOF
  > }
  > __EOF__
  $ . "$TESTTMP/copytrace.sh"

  $ cat >> $HGRCPATH << EOF
  > [extensions]
  > rebase=
  > shelve=
  > EOF

NOTE: calling initclient() set copytrace.sourcecommitlimit=-1 as we want to
prevent the full copytrace algorithm to run and test the heuristic algorithm
without complexing the test cases with public and draft commits.

Check filename heuristics (same dirname and same basename)
----------------------------------------------------------

  $ hg init repo
  $ initclient repo
  $ cd repo
  $ echo a > a
  $ mkdir dir
  $ echo a > dir/file.txt
  $ hg addremove
  adding a
  adding dir/file.txt
  $ hg ci -m initial
  $ hg mv a b
  $ hg mv -q dir dir2
  $ hg ci -m 'mv a b, mv dir/ dir2/'
  $ hg up -q 0
  $ echo b > a
  $ echo b > dir/file.txt
  $ hg ci -qm 'mod a, mod dir/file.txt'

  $ hg log -G -T 'changeset: {node}\n desc: {desc}\n'
  @  changeset: 557f403c0afd2a3cf15d7e2fb1f1001a8b85e081
  |   desc: mod a, mod dir/file.txt
  | o  changeset: 928d74bc9110681920854d845c06959f6dfc9547
  |/    desc: mv a b, mv dir/ dir2/
  o  changeset: 3c482b16e54596fed340d05ffaf155f156cda7ee
      desc: initial

  $ hg rebase -s . -d 1
  rebasing 2:557f403c0afd "mod a, mod dir/file.txt" (tip)
  merging b and a to b
  merging dir2/file.txt and dir/file.txt to dir2/file.txt
  saved backup bundle to $TESTTMP/repo/.hg/strip-backup/557f403c0afd-9926eeff-rebase.hg
  $ cd ..
  $ rm -rf repo

Make sure filename heuristics do not when they are not related
--------------------------------------------------------------

  $ hg init repo
  $ initclient repo
  $ cd repo
  $ echo 'somecontent' > a
  $ hg add a
  $ hg ci -m initial
  $ hg rm a
  $ echo 'completelydifferentcontext' > b
  $ hg add b
  $ hg ci -m 'rm a, add b'
  $ hg up -q 0
  $ printf 'somecontent\nmoarcontent' > a
  $ hg ci -qm 'mode a'

  $ hg log -G -T 'changeset: {node}\n desc: {desc}\n'
  @  changeset: d526312210b9e8f795d576a77dc643796384d86e
  |   desc: mode a
  | o  changeset: 46985f76c7e5e5123433527f5c8526806145650b
  |/    desc: rm a, add b
  o  changeset: e5b71fb099c29d9172ef4a23485aaffd497e4cc0
      desc: initial

  $ hg rebase -s . -d 1
  rebasing 2:d526312210b9 "mode a" (tip)
  other [source] changed a which local [dest] deleted
  use (c)hanged version, leave (d)eleted, or leave (u)nresolved? u
  unresolved conflicts (see hg resolve, then hg rebase --continue)
  [1]

  $ cd ..
  $ rm -rf repo

Test when lca didn't modified the file that was moved
-----------------------------------------------------

  $ hg init repo
  $ initclient repo
  $ cd repo
  $ echo 'somecontent' > a
  $ hg add a
  $ hg ci -m initial
  $ echo c > c
  $ hg add c
  $ hg ci -m randomcommit
  $ hg mv a b
  $ hg ci -m 'mv a b'
  $ hg up -q 1
  $ echo b > a
  $ hg ci -qm 'mod a'

  $ hg log -G -T 'changeset: {node}\n desc: {desc}, phase: {phase}\n'
  @  changeset: 9d5cf99c3d9f8e8b05ba55421f7f56530cfcf3bc
  |   desc: mod a, phase: draft
  | o  changeset: d760186dd240fc47b91eb9f0b58b0002aaeef95d
  |/    desc: mv a b, phase: draft
  o  changeset: 48e1b6ba639d5d7fb313fa7989eebabf99c9eb83
  |   desc: randomcommit, phase: draft
  o  changeset: e5b71fb099c29d9172ef4a23485aaffd497e4cc0
      desc: initial, phase: draft

  $ hg rebase -s . -d 2
  rebasing 3:9d5cf99c3d9f "mod a" (tip)
  merging b and a to b
  saved backup bundle to $TESTTMP/repo/.hg/strip-backup/9d5cf99c3d9f-f02358cc-rebase.hg
  $ cd ..
  $ rm -rf repo

Rebase "backwards"
------------------

  $ hg init repo
  $ initclient repo
  $ cd repo
  $ echo 'somecontent' > a
  $ hg add a
  $ hg ci -m initial
  $ echo c > c
  $ hg add c
  $ hg ci -m randomcommit
  $ hg mv a b
  $ hg ci -m 'mv a b'
  $ hg up -q 2
  $ echo b > b
  $ hg ci -qm 'mod b'

  $ hg log -G -T 'changeset: {node}\n desc: {desc}\n'
  @  changeset: fbe97126b3969056795c462a67d93faf13e4d298
  |   desc: mod b
  o  changeset: d760186dd240fc47b91eb9f0b58b0002aaeef95d
  |   desc: mv a b
  o  changeset: 48e1b6ba639d5d7fb313fa7989eebabf99c9eb83
  |   desc: randomcommit
  o  changeset: e5b71fb099c29d9172ef4a23485aaffd497e4cc0
      desc: initial

  $ hg rebase -s . -d 0
  rebasing 3:fbe97126b396 "mod b" (tip)
  merging a and b to a
  saved backup bundle to $TESTTMP/repo/.hg/strip-backup/fbe97126b396-cf5452a1-rebase.hg
  $ cd ..
  $ rm -rf repo

Check a few potential move candidates
-------------------------------------

  $ hg init repo
  $ initclient repo
  $ cd repo
  $ mkdir dir
  $ echo a > dir/a
  $ hg add dir/a
  $ hg ci -qm initial
  $ hg mv dir/a dir/b
  $ hg ci -qm 'mv dir/a dir/b'
  $ mkdir dir2
  $ echo b > dir2/a
  $ hg add dir2/a
  $ hg ci -qm 'create dir2/a'
  $ hg up -q 0
  $ echo b > dir/a
  $ hg ci -qm 'mod dir/a'

  $ hg log -G -T 'changeset: {node}\n desc: {desc}\n'
  @  changeset: 6b2f4cece40fd320f41229f23821256ffc08efea
  |   desc: mod dir/a
  | o  changeset: 4494bf7efd2e0dfdd388e767fb913a8a3731e3fa
  | |   desc: create dir2/a
  | o  changeset: b1784dfab6ea6bfafeb11c0ac50a2981b0fe6ade
  |/    desc: mv dir/a dir/b
  o  changeset: 36859b8907c513a3a87ae34ba5b1e7eea8c20944
      desc: initial

  $ hg rebase -s . -d 2
  rebasing 3:6b2f4cece40f "mod dir/a" (tip)
  merging dir/b and dir/a to dir/b
  saved backup bundle to $TESTTMP/repo/.hg/strip-backup/6b2f4cece40f-503efe60-rebase.hg
  $ cd ..
  $ rm -rf repo

Test the copytrace.movecandidateslimit with many move candidates
----------------------------------------------------------------

  $ hg init repo
  $ initclient repo
  $ cd repo
  $ echo a > a
  $ hg add a
  $ hg ci -m initial
  $ hg mv a foo
  $ echo a > b
  $ echo a > c
  $ echo a > d
  $ echo a > e
  $ echo a > f
  $ echo a > g
  $ hg add b
  $ hg add c
  $ hg add d
  $ hg add e
  $ hg add f
  $ hg add g
  $ hg ci -m 'mv a foo, add many files'
  $ hg up -q ".^"
  $ echo b > a
  $ hg ci -m 'mod a'
  created new head

  $ hg log -G -T 'changeset: {node}\n desc: {desc}\n'
  @  changeset: ef716627c70bf4ca0bdb623cfb0d6fe5b9acc51e
  |   desc: mod a
  | o  changeset: 8329d5c6bf479ec5ca59b9864f3f45d07213f5a4
  |/    desc: mv a foo, add many files
  o  changeset: 1451231c87572a7d3f92fc210b4b35711c949a98
      desc: initial

With small limit

  $ hg rebase -s 2 -d 1 --config experimental.copytrace.movecandidateslimit=0
  rebasing 2:ef716627c70b "mod a" (tip)
  skipping copytracing for 'a', more candidates than the limit: 7
  other [source] changed a which local [dest] deleted
  use (c)hanged version, leave (d)eleted, or leave (u)nresolved? u
  unresolved conflicts (see hg resolve, then hg rebase --continue)
  [1]

  $ hg rebase --abort
  rebase aborted

With default limit which is 100

  $ hg rebase -s 2 -d 1
  rebasing 2:ef716627c70b "mod a" (tip)
  merging foo and a to foo
  saved backup bundle to $TESTTMP/repo/.hg/strip-backup/ef716627c70b-24681561-rebase.hg

  $ cd ..
  $ rm -rf repo

Move file in one branch and delete it in another
-----------------------------------------------

  $ hg init repo
  $ initclient repo
  $ cd repo
  $ echo a > a
  $ hg add a
  $ hg ci -m initial
  $ hg mv a b
  $ hg ci -m 'mv a b'
  $ hg up -q ".^"
  $ hg rm a
  $ hg ci -m 'del a'
  created new head

  $ hg log -G -T 'changeset: {node}\n desc: {desc}, phase: {phase}\n'
  @  changeset: 7d61ee3b1e48577891a072024968428ba465c47b
  |   desc: del a, phase: draft
  | o  changeset: 472e38d57782172f6c6abed82a94ca0d998c3a22
  |/    desc: mv a b, phase: draft
  o  changeset: 1451231c87572a7d3f92fc210b4b35711c949a98
      desc: initial, phase: draft

  $ hg rebase -s 1 -d 2
  rebasing 1:472e38d57782 "mv a b"
  saved backup bundle to $TESTTMP/repo/.hg/strip-backup/472e38d57782-17d50e29-rebase.hg
  $ hg up -q c492ed3c7e35dcd1dc938053b8adf56e2cfbd062
  $ ls
  b
  $ cd ..
  $ rm -rf repo

Move a directory in draft branch
--------------------------------

  $ hg init repo
  $ initclient repo
  $ cd repo
  $ mkdir dir
  $ echo a > dir/a
  $ hg add dir/a
  $ hg ci -qm initial
  $ echo b > dir/a
  $ hg ci -qm 'mod dir/a'
  $ hg up -q ".^"
  $ hg mv -q dir/ dir2
  $ hg ci -qm 'mv dir/ dir2/'

  $ hg log -G -T 'changeset: {node}\n desc: {desc}\n'
  @  changeset: a33d80b6e352591dfd82784e1ad6cdd86b25a239
  |   desc: mv dir/ dir2/
  | o  changeset: 6b2f4cece40fd320f41229f23821256ffc08efea
  |/    desc: mod dir/a
  o  changeset: 36859b8907c513a3a87ae34ba5b1e7eea8c20944
      desc: initial

  $ hg rebase -s . -d 1
  rebasing 2:a33d80b6e352 "mv dir/ dir2/" (tip)
  merging dir/a and dir2/a to dir2/a
  saved backup bundle to $TESTTMP/repo/.hg/strip-backup/a33d80b6e352-fecb9ada-rebase.hg
  $ cd ..
  $ rm -rf server
  $ rm -rf repo

Move file twice and rebase mod on top of moves
----------------------------------------------

  $ hg init repo
  $ initclient repo
  $ cd repo
  $ echo a > a
  $ hg add a
  $ hg ci -m initial
  $ hg mv a b
  $ hg ci -m 'mv a b'
  $ hg mv b c
  $ hg ci -m 'mv b c'
  $ hg up -q 0
  $ echo c > a
  $ hg ci -m 'mod a'
  created new head

  $ hg log -G -T 'changeset: {node}\n desc: {desc}\n'
  @  changeset: d413169422167a3fa5275fc5d71f7dea9f5775f3
  |   desc: mod a
  | o  changeset: d3efd280421d24f9f229997c19e654761c942a71
  | |   desc: mv b c
  | o  changeset: 472e38d57782172f6c6abed82a94ca0d998c3a22
  |/    desc: mv a b
  o  changeset: 1451231c87572a7d3f92fc210b4b35711c949a98
      desc: initial
  $ hg rebase -s . -d 2
  rebasing 3:d41316942216 "mod a" (tip)
  merging c and a to c
  saved backup bundle to $TESTTMP/repo/.hg/strip-backup/d41316942216-2b5949bc-rebase.hg

  $ cd ..
  $ rm -rf repo

Move file twice and rebase moves on top of mods
-----------------------------------------------

  $ hg init repo
  $ initclient repo
  $ cd repo
  $ echo a > a
  $ hg add a
  $ hg ci -m initial
  $ hg mv a b
  $ hg ci -m 'mv a b'
  $ hg mv b c
  $ hg ci -m 'mv b c'
  $ hg up -q 0
  $ echo c > a
  $ hg ci -m 'mod a'
  created new head
  $ hg log -G -T 'changeset: {node}\n desc: {desc}\n'
  @  changeset: d413169422167a3fa5275fc5d71f7dea9f5775f3
  |   desc: mod a
  | o  changeset: d3efd280421d24f9f229997c19e654761c942a71
  | |   desc: mv b c
  | o  changeset: 472e38d57782172f6c6abed82a94ca0d998c3a22
  |/    desc: mv a b
  o  changeset: 1451231c87572a7d3f92fc210b4b35711c949a98
      desc: initial
  $ hg rebase -s 1 -d .
  rebasing 1:472e38d57782 "mv a b"
  merging a and b to b
  rebasing 2:d3efd280421d "mv b c"
  merging b and c to c
  saved backup bundle to $TESTTMP/repo/.hg/strip-backup/472e38d57782-ab8d3c58-rebase.hg

  $ cd ..
  $ rm -rf repo

Move one file and add another file in the same folder in one branch, modify file in another branch
--------------------------------------------------------------------------------------------------

  $ hg init repo
  $ initclient repo
  $ cd repo
  $ echo a > a
  $ hg add a
  $ hg ci -m initial
  $ hg mv a b
  $ hg ci -m 'mv a b'
  $ echo c > c
  $ hg add c
  $ hg ci -m 'add c'
  $ hg up -q 0
  $ echo b > a
  $ hg ci -m 'mod a'
  created new head

  $ hg log -G -T 'changeset: {node}\n desc: {desc}\n'
  @  changeset: ef716627c70bf4ca0bdb623cfb0d6fe5b9acc51e
  |   desc: mod a
  | o  changeset: b1a6187e79fbce851bb584eadcb0cc4a80290fd9
  | |   desc: add c
  | o  changeset: 472e38d57782172f6c6abed82a94ca0d998c3a22
  |/    desc: mv a b
  o  changeset: 1451231c87572a7d3f92fc210b4b35711c949a98
      desc: initial

  $ hg rebase -s . -d 2
  rebasing 3:ef716627c70b "mod a" (tip)
  merging b and a to b
  saved backup bundle to $TESTTMP/repo/.hg/strip-backup/ef716627c70b-24681561-rebase.hg
  $ ls
  b
  c
  $ cat b
  b
  $ rm -rf repo

Merge test
----------

  $ hg init repo
  $ initclient repo
  $ cd repo
  $ echo a > a
  $ hg add a
  $ hg ci -m initial
  $ echo b > a
  $ hg ci -m 'modify a'
  $ hg up -q 0
  $ hg mv a b
  $ hg ci -m 'mv a b'
  created new head
  $ hg up -q 2

  $ hg log -G -T 'changeset: {node}\n desc: {desc}\n'
  @  changeset: 472e38d57782172f6c6abed82a94ca0d998c3a22
  |   desc: mv a b
  | o  changeset: b0357b07f79129a3d08a68621271ca1352ae8a09
  |/    desc: modify a
  o  changeset: 1451231c87572a7d3f92fc210b4b35711c949a98
      desc: initial

  $ hg merge 1
  merging b and a to b
  0 files updated, 1 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -m merge
  $ ls
  b
  $ cd ..
  $ rm -rf repo

Copy and move file
------------------

  $ hg init repo
  $ initclient repo
  $ cd repo
  $ echo a > a
  $ hg add a
  $ hg ci -m initial
  $ hg cp a c
  $ hg mv a b
  $ hg ci -m 'cp a c, mv a b'
  $ hg up -q 0
  $ echo b > a
  $ hg ci -m 'mod a'
  created new head

  $ hg log -G -T 'changeset: {node}\n desc: {desc}\n'
  @  changeset: ef716627c70bf4ca0bdb623cfb0d6fe5b9acc51e
  |   desc: mod a
  | o  changeset: 4fc3fd13fbdb89ada6b75bfcef3911a689a0dde8
  |/    desc: cp a c, mv a b
  o  changeset: 1451231c87572a7d3f92fc210b4b35711c949a98
      desc: initial

  $ hg rebase -s . -d 1
  rebasing 2:ef716627c70b "mod a" (tip)
  merging b and a to b
  merging c and a to c
  saved backup bundle to $TESTTMP/repo/repo/.hg/strip-backup/ef716627c70b-24681561-rebase.hg
  $ ls
  b
  c
  $ cat b
  b
  $ cat c
  b
  $ cd ..
  $ rm -rf repo

Do a merge commit with many consequent moves in one branch
----------------------------------------------------------

  $ hg init repo
  $ initclient repo
  $ cd repo
  $ echo a > a
  $ hg add a
  $ hg ci -m initial
  $ echo b > a
  $ hg ci -qm 'mod a'
  $ hg up -q ".^"
  $ hg mv a b
  $ hg ci -qm 'mv a b'
  $ hg mv b c
  $ hg ci -qm 'mv b c'
  $ hg up -q 1
  $ hg log -G -T 'changeset: {node}\n desc: {desc}\n'
  o  changeset: d3efd280421d24f9f229997c19e654761c942a71
  |   desc: mv b c
  o  changeset: 472e38d57782172f6c6abed82a94ca0d998c3a22
  |   desc: mv a b
  | @  changeset: ef716627c70bf4ca0bdb623cfb0d6fe5b9acc51e
  |/    desc: mod a
  o  changeset: 1451231c87572a7d3f92fc210b4b35711c949a98
      desc: initial

  $ hg merge 3
  merging a and c to c
  0 files updated, 1 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -qm 'merge'
  $ hg log -G -T 'changeset: {node}\n desc: {desc}, phase: {phase}\n'
  @    changeset: cd29b0d08c0f39bfed4cde1b40e30f419db0c825
  |\    desc: merge, phase: draft
  | o  changeset: d3efd280421d24f9f229997c19e654761c942a71
  | |   desc: mv b c, phase: draft
  | o  changeset: 472e38d57782172f6c6abed82a94ca0d998c3a22
  | |   desc: mv a b, phase: draft
  o |  changeset: ef716627c70bf4ca0bdb623cfb0d6fe5b9acc51e
  |/    desc: mod a, phase: draft
  o  changeset: 1451231c87572a7d3f92fc210b4b35711c949a98
      desc: initial, phase: draft
  $ ls
  c
  $ cd ..
  $ rm -rf repo

Test shelve/unshelve
-------------------

  $ hg init repo
  $ initclient repo
  $ cd repo
  $ echo a > a
  $ hg add a
  $ hg ci -m initial
  $ echo b > a
  $ hg shelve
  shelved as default
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg mv a b
  $ hg ci -m 'mv a b'

  $ hg log -G -T 'changeset: {node}\n desc: {desc}\n'
  @  changeset: 472e38d57782172f6c6abed82a94ca0d998c3a22
  |   desc: mv a b
  o  changeset: 1451231c87572a7d3f92fc210b4b35711c949a98
      desc: initial
  $ hg unshelve
  unshelving change 'default'
  rebasing shelved changes
  rebasing 2:45f63161acea "changes to: initial" (tip)
  merging b and a to b
  $ ls
  b
  $ cat b
  b
  $ cd ..
  $ rm -rf repo

Test full copytrace ability on draft branch
-------------------------------------------

File directory and base name changed in same move
  $ hg init repo
  $ initclient repo
  $ mkdir repo/dir1
  $ cd repo/dir1
  $ echo a > a
  $ hg add a
  $ hg ci -qm initial
  $ cd ..
  $ hg mv -q dir1 dir2
  $ hg mv dir2/a dir2/b
  $ hg ci -qm 'mv a b; mv dir1 dir2'
  $ hg up -q '.^'
  $ cd dir1
  $ echo b >> a
  $ cd ..
  $ hg ci -qm 'mod a'

  $ hg log -G -T 'changeset {node}\n desc {desc}, phase: {phase}\n'
  @  changeset 6207d2d318e710b882e3d5ada2a89770efc42c96
  |   desc mod a, phase: draft
  | o  changeset abffdd4e3dfc04bc375034b970299b2a309a1cce
  |/    desc mv a b; mv dir1 dir2, phase: draft
  o  changeset 81973cd24b58db2fdf18ce3d64fb2cc3284e9ab3
      desc initial, phase: draft

  $ hg rebase -s . -d 1 --config experimental.copytrace.sourcecommitlimit=100
  rebasing 2:6207d2d318e7 "mod a" (tip)
  merging dir2/b and dir1/a to dir2/b
  saved backup bundle to $TESTTMP/repo/repo/.hg/strip-backup/6207d2d318e7-1c9779ad-rebase.hg
  $ cat dir2/b
  a
  b
  $ cd ..
  $ rm -rf repo

Move directory in one merge parent, while adding file to original directory
in other merge parent. File moved on rebase.

  $ hg init repo
  $ initclient repo
  $ mkdir repo/dir1
  $ cd repo/dir1
  $ echo dummy > dummy
  $ hg add dummy
  $ cd ..
  $ hg ci -qm initial
  $ cd dir1
  $ echo a > a
  $ hg add a
  $ cd ..
  $ hg ci -qm 'hg add dir1/a'
  $ hg up -q '.^'
  $ hg mv -q dir1 dir2
  $ hg ci -qm 'mv dir1 dir2'

  $ hg log -G -T 'changeset {node}\n desc {desc}, phase: {phase}\n'
  @  changeset e8919e7df8d036e07b906045eddcd4a42ff1915f
  |   desc mv dir1 dir2, phase: draft
  | o  changeset 7c7c6f339be00f849c3cb2df738ca91db78b32c8
  |/    desc hg add dir1/a, phase: draft
  o  changeset a235dcce55dcf42034c4e374cb200662d0bb4a13
      desc initial, phase: draft

  $ hg rebase -s . -d 1 --config experimental.copytrace.sourcecommitlimit=100
  rebasing 2:e8919e7df8d0 "mv dir1 dir2" (tip)
  saved backup bundle to $TESTTMP/repo/repo/.hg/strip-backup/e8919e7df8d0-f62fab62-rebase.hg
  $ ls dir2
  a
  dummy
  $ rm -rf repo

Testing the sourcecommitlimit config
-----------------------------------

  $ hg init repo
  $ initclient repo
  $ cd repo
  $ echo a > a
  $ hg ci -Aqm "added a"
  $ echo "more things" >> a
  $ hg ci -qm "added more things to a"
  $ hg up 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo b > b
  $ hg ci -Aqm "added b"
  $ mkdir foo
  $ hg mv a foo/bar
  $ hg ci -m "Moved a to foo/bar"
  $ hg log -G -T 'changeset {node}\n desc {desc}, phase: {phase}\n'
  @  changeset b4b0f7880e500b5c364a5f07b4a2b167de7a6fb0
  |   desc Moved a to foo/bar, phase: draft
  o  changeset 5f6d8a4bf34ab274ccc9f631c2536964b8a3666d
  |   desc added b, phase: draft
  | o  changeset 8b6e13696c38e8445a759516474640c2f8dddef6
  |/    desc added more things to a, phase: draft
  o  changeset 9092f1db7931481f93b37d5c9fbcfc341bcd7318
      desc added a, phase: draft

When the sourcecommitlimit is small and we have more drafts, we use heuristics only

  $ hg rebase -s 8b6e13696 -d .
  rebasing 1:8b6e13696c38 "added more things to a"
  other [source] changed a which local [dest] deleted
  use (c)hanged version, leave (d)eleted, or leave (u)nresolved? u
  unresolved conflicts (see hg resolve, then hg rebase --continue)
  [1]

But when we have "sourcecommitlimit > (no. of drafts from base to c1)", we do
fullcopytracing

  $ hg rebase --abort
  rebase aborted
  $ hg rebase -s 8b6e13696 -d . --config experimental.copytrace.sourcecommitlimit=100
  rebasing 1:8b6e13696c38 "added more things to a"
  merging foo/bar and a to foo/bar
  saved backup bundle to $TESTTMP/repo/repo/repo/.hg/strip-backup/8b6e13696c38-fc14ac83-rebase.hg
  $ cd ..
  $ rm -rf repo