annotate tests/test-copies-chain-merge.t @ 44459:6f1f4a6f4168

copies-tests: add a case where a file is deleted/added but with a merge

This is a case similar to DB/BD, but in this case the other branch updated the
file. So an actual merge happens and the two "independant" file history has to
be merged.

Differential Revision: https://phab.mercurial-scm.org/D8241

=====================================================
Test Copy tracing for chain of copies involving merge
=====================================================

This test files covers copies/rename case for a chains of commit where merges
are involved. It cheks we do not have unwanted update of behavior and that the
different options to retrieve copies behave correctly.

Setup
=====

use git diff to see rename

  $ cat << EOF >> $HGRCPATH
  > [diff]
  > git=yes
  > [ui]
  > logtemplate={rev} {desc}]\n
  > EOF

  $ hg init repo-chain
  $ cd repo-chain

Add some linear rename initialy

  $ touch a b h
  $ hg ci -Am 'i-0 initial commit: a b h'
  adding a
  adding b
  adding h
  $ hg mv a c
  $ hg ci -Am 'i-1: a -move-> c'
  $ hg mv c d
  $ hg ci -Am 'i-2: c -move-> d'
  $ hg log -G
  @  2 i-2: c -move-> d]
  |
  o  1 i-1: a -move-> c]
  |
  o  0 i-0 initial commit: a b h]
  

And having another branch with renames on the other side

  $ hg mv d e
  $ hg ci -Am 'a-1: d -move-> e'
  $ hg mv e f
  $ hg ci -Am 'a-2: e -move-> f'
  $ hg log -G --rev '::.'
  @  4 a-2: e -move-> f]
  |
  o  3 a-1: d -move-> e]
  |
  o  2 i-2: c -move-> d]
  |
  o  1 i-1: a -move-> c]
  |
  o  0 i-0 initial commit: a b h]
  

Have a branching with nothing on one side

  $ hg up 'desc("i-2")'
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ echo foo > b
  $ hg ci -m 'b-1: b update'
  created new head
  $ hg log -G --rev '::.'
  @  5 b-1: b update]
  |
  o  2 i-2: c -move-> d]
  |
  o  1 i-1: a -move-> c]
  |
  o  0 i-0 initial commit: a b h]
  


Merge the two branches we just defined (in both directions)
- one with change to an unrelated file
- one with renames in them

  $ hg up 'desc("b-1")'
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg merge 'desc("a-2")'
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -m 'mBAm-0 simple merge - one way'
  $ hg up 'desc("a-2")'
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg merge 'desc("b-1")'
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -m 'mABm-0 simple merge - the other way'
  created new head
  $ hg log -G --rev '::(desc("mABm")+desc("mBAm"))'
  @    7 mABm-0 simple merge - the other way]
  |\
  +---o  6 mBAm-0 simple merge - one way]
  | |/
  | o  5 b-1: b update]
  | |
  o |  4 a-2: e -move-> f]
  | |
  o |  3 a-1: d -move-> e]
  |/
  o  2 i-2: c -move-> d]
  |
  o  1 i-1: a -move-> c]
  |
  o  0 i-0 initial commit: a b h]
  

Create a branch that delete a file previous renamed

  $ hg up 'desc("i-2")'
  2 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ hg rm d
  $ hg ci -m 'c-1 delete d'
  created new head
  $ hg log -G --rev '::.'
  @  8 c-1 delete d]
  |
  o  2 i-2: c -move-> d]
  |
  o  1 i-1: a -move-> c]
  |
  o  0 i-0 initial commit: a b h]
  

Merge:
- one with change to an unrelated file
- one deleting the change
and recreate an unrelated file after the merge

  $ hg up 'desc("b-1")'
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg merge 'desc("c-1")'
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -m 'mBCm-0 simple merge - one way'
  $ echo bar > d
  $ hg add d
  $ hg ci -m 'mBCm-1 re-add d'
  $ hg up 'desc("c-1")'
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ hg merge 'desc("b-1")'
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -m 'mCBm-0 simple merge - the other way'
  created new head
  $ echo bar > d
  $ hg add d
  $ hg ci -m 'mCBm-1 re-add d'
  $ hg log -G --rev '::(desc("mCBm")+desc("mBCm"))'
  @  12 mCBm-1 re-add d]
  |
  o    11 mCBm-0 simple merge - the other way]
  |\
  | | o  10 mBCm-1 re-add d]
  | | |
  +---o  9 mBCm-0 simple merge - one way]
  | |/
  | o  8 c-1 delete d]
  | |
  o |  5 b-1: b update]
  |/
  o  2 i-2: c -move-> d]
  |
  o  1 i-1: a -move-> c]
  |
  o  0 i-0 initial commit: a b h]
  

Create a branch that delete a file previous renamed and recreate it

  $ hg up 'desc("i-2")'
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg rm d
  $ hg ci -m 'd-1 delete d'
  created new head
  $ echo bar > d
  $ hg add d
  $ hg ci -m 'd-2 re-add d'
  $ hg log -G --rev '::.'
  @  14 d-2 re-add d]
  |
  o  13 d-1 delete d]
  |
  o  2 i-2: c -move-> d]
  |
  o  1 i-1: a -move-> c]
  |
  o  0 i-0 initial commit: a b h]
  

Merge:
- one with change to an unrelated file
- one deleting and recreating the file

Note:
| In this case, the merge get conflicting information since on one side we have
| a "brand new" d. and one the other one we have "d renamed from c (itself
| renamed from c)".
|
| The current code arbitrarily pick one side

  $ hg up 'desc("b-1")'
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg merge 'desc("d-2")'
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -m 'mBDm-0 simple merge - one way'
  $ hg up 'desc("d-2")'
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg merge 'desc("b-1")'
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -m 'mDBm-0 simple merge - the other way'
  created new head
  $ hg log -G --rev '::(desc("mDBm")+desc("mBDm"))'
  @    16 mDBm-0 simple merge - the other way]
  |\
  +---o  15 mBDm-0 simple merge - one way]
  | |/
  | o  14 d-2 re-add d]
  | |
  | o  13 d-1 delete d]
  | |
  o |  5 b-1: b update]
  |/
  o  2 i-2: c -move-> d]
  |
  o  1 i-1: a -move-> c]
  |
  o  0 i-0 initial commit: a b h]
  

Having another branch renaming a different file to the same filename as another

  $ hg up 'desc("i-2")'
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg mv b g
  $ hg ci -m 'e-1 b -move-> g'
  created new head
  $ hg mv g f
  $ hg ci -m 'e-2 g -move-> f'
  $ hg log -G --rev '::.'
  @  18 e-2 g -move-> f]
  |
  o  17 e-1 b -move-> g]
  |
  o  2 i-2: c -move-> d]
  |
  o  1 i-1: a -move-> c]
  |
  o  0 i-0 initial commit: a b h]
  

Merge:
- the "e-" branch renaming b to f (through 'g')
- the "a-" branch renaming d to f (through e)

  $ hg up 'desc("a-2")'
  2 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ hg merge 'desc("e-2")'
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -m 'mAEm-0 simple merge - one way'
  $ hg up 'desc("e-2")'
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg merge 'desc("a-2")'
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -m 'mEAm-0 simple merge - the other way'
  created new head
  $ hg log -G --rev '::(desc("mAEm")+desc("mEAm"))'
  @    20 mEAm-0 simple merge - the other way]
  |\
  +---o  19 mAEm-0 simple merge - one way]
  | |/
  | o  18 e-2 g -move-> f]
  | |
  | o  17 e-1 b -move-> g]
  | |
  o |  4 a-2: e -move-> f]
  | |
  o |  3 a-1: d -move-> e]
  |/
  o  2 i-2: c -move-> d]
  |
  o  1 i-1: a -move-> c]
  |
  o  0 i-0 initial commit: a b h]
  

Note:
| In this case, one of the merge wrongly record a merge while there is none.
| This lead to bad copy tracing information to be dug up.


Merge:
- one with change to an unrelated file (b)
- one overwriting a file (d) with a rename (from h to i to d)

  $ hg up 'desc("i-2")'
  2 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ hg mv h i
  $ hg commit -m "f-1: rename h -> i"
  created new head
  $ hg mv --force i d
  $ hg commit -m "f-2: rename i -> d"
  $ hg debugindex d
     rev linkrev nodeid       p1           p2
       0       2 01c2f5eabdc4 000000000000 000000000000
       1      10 b004912a8510 000000000000 000000000000
       2      15 0bb5445dc4d0 01c2f5eabdc4 b004912a8510
       3      22 c72365ee036f 000000000000 000000000000
  $ hg up 'desc("b-1")'
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg merge 'desc("f-2")'
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -m 'mBFm-0 simple merge - one way'
  $ hg up 'desc("f-2")'
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg merge 'desc("b-1")'
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -m 'mFBm-0 simple merge - the other way'
  created new head
  $ hg log -G --rev '::(desc("mBFm")+desc("mFBm"))'
  @    24 mFBm-0 simple merge - the other way]
  |\
  +---o  23 mBFm-0 simple merge - one way]
  | |/
  | o  22 f-2: rename i -> d]
  | |
  | o  21 f-1: rename h -> i]
  | |
  o |  5 b-1: b update]
  |/
  o  2 i-2: c -move-> d]
  |
  o  1 i-1: a -move-> c]
  |
  o  0 i-0 initial commit: a b h]
  

Merge:
- one with change to a file
- one deleting and recreating the file

  $ hg up 'desc("i-2")'
  3 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ echo "some update" >> d
  $ hg commit -m "g-1: update d"
  created new head
  $ hg up 'desc("d-2")'
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg merge 'desc("g-1")' --tool :union
  merging d
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -m 'mDGm-0 simple merge - one way'
  $ hg up 'desc("g-1")'
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg merge 'desc("d-2")' --tool :union
  merging d
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -m 'mGDm-0 simple merge - the other way'
  created new head
  $ hg log -G --rev '::(desc("mDGm")+desc("mGDm"))'
  @    27 mGDm-0 simple merge - the other way]
  |\
  +---o  26 mDGm-0 simple merge - one way]
  | |/
  | o  25 g-1: update d]
  | |
  o |  14 d-2 re-add d]
  | |
  o |  13 d-1 delete d]
  |/
  o  2 i-2: c -move-> d]
  |
  o  1 i-1: a -move-> c]
  |
  o  0 i-0 initial commit: a b h]
  


Check results
=============

merging with unrelated change does not interfer wit the renames
---------------------------------------------------------------

- rename on one side
- unrelated change on the other side

  $ hg status --copies --rev 'desc("b-1")' --rev 'desc("mABm")'
  A f
    d
  R d
  $ hg status --copies --rev 'desc("b-1")' --rev 'desc("mBAm")'
  A f
    d
  R d
  $ hg status --copies --rev 'desc("a-2")' --rev 'desc("mABm")'
  M b
  $ hg status --copies --rev 'desc("a-2")' --rev 'desc("mBAm")'
  M b
  $ hg status --copies --rev 'desc("i-2")' --rev 'desc("mABm")'
  M b
  A f
    d
  R d
  $ hg status --copies --rev 'desc("i-2")' --rev 'desc("mBAm")'
  M b
  A f
    d
  R d
  $ hg status --copies --rev 'desc("i-0")' --rev 'desc("mABm")'
  M b
  A f
    a
  R a
  $ hg status --copies --rev 'desc("i-0")' --rev 'desc("mBAm")'
  M b
  A f
    a
  R a

merging with the side having a delete
-------------------------------------

case summary:
- one with change to an unrelated file
- one deleting the change
and recreate an unrelated file after the merge

checks:
- comparing from the merge

  $ hg status --copies --rev 'desc("b-1")' --rev 'desc("mBCm-0")'
  R d
  $ hg status --copies --rev 'desc("b-1")' --rev 'desc("mCBm-0")'
  R d
  $ hg status --copies --rev 'desc("c-1")' --rev 'desc("mBCm-0")'
  M b
  $ hg status --copies --rev 'desc("c-1")' --rev 'desc("mCBm-0")'
  M b
  $ hg status --copies --rev 'desc("i-2")' --rev 'desc("mBCm-0")'
  M b
  R d
  $ hg status --copies --rev 'desc("i-2")' --rev 'desc("mCBm-0")'
  M b
  R d
  $ hg status --copies --rev 'desc("i-0")' --rev 'desc("mBCm-0")'
  M b
  R a
  $ hg status --copies --rev 'desc("i-0")' --rev 'desc("mCBm-0")'
  M b
  R a

- comparing with the merge children re-adding the file

  $ hg status --copies --rev 'desc("b-1")' --rev 'desc("mBCm-1")'
  M d
  $ hg status --copies --rev 'desc("b-1")' --rev 'desc("mCBm-1")'
  M d
  $ hg status --copies --rev 'desc("c-1")' --rev 'desc("mBCm-1")'
  M b
  A d
  $ hg status --copies --rev 'desc("c-1")' --rev 'desc("mCBm-1")'
  M b
  A d
  $ hg status --copies --rev 'desc("i-2")' --rev 'desc("mBCm-1")'
  M b
  M d
  $ hg status --copies --rev 'desc("i-2")' --rev 'desc("mCBm-1")'
  M b
  M d
  $ hg status --copies --rev 'desc("i-0")' --rev 'desc("mBCm-1")'
  M b
  A d
  R a
  $ hg status --copies --rev 'desc("i-0")' --rev 'desc("mCBm-1")'
  M b
  A d
  R a

Comparing with a merge re-adding the file afterward
---------------------------------------------------

Merge:
- one with change to an unrelated file
- one deleting and recreating the change

Note:
| In this case, one of the merge wrongly record a merge while there is none.
| This lead to bad copy tracing information to be dug up.

  $ hg status --copies --rev 'desc("b-1")' --rev 'desc("mBDm-0")'
  M d
  $ hg status --copies --rev 'desc("b-1")' --rev 'desc("mDBm-0")'
  M d
  $ hg status --copies --rev 'desc("d-2")' --rev 'desc("mBDm-0")'
  M b
  M d
  $ hg status --copies --rev 'desc("d-2")' --rev 'desc("mDBm-0")'
  M b
  $ hg status --copies --rev 'desc("i-2")' --rev 'desc("mBDm-0")'
  M b
  M d
  $ hg status --copies --rev 'desc("i-2")' --rev 'desc("mDBm-0")'
  M b
  M d

The bugs makes recorded copy is different depending of where we started the merge from since

  $ hg manifest --debug --rev 'desc("mBDm-0")' | grep '644   d'
  0bb5445dc4d02f4e0d86cf16f9f3a411d0f17744 644   d
  $ hg manifest --debug --rev 'desc("mDBm-0")' | grep '644   d'
  b004912a8510032a0350a74daa2803dadfb00e12 644   d

The 0bb5445dc4d02f4e0d86cf16f9f3a411d0f17744 entry is wrong, since the file was
deleted on one side (then recreate) and untouched on the other side, no "merge"
has happened. The resulting `d` file is the untouched version from branch `D`,
not a merge.

  $ hg manifest --debug --rev 'desc("d-2")' | grep '644   d'
  b004912a8510032a0350a74daa2803dadfb00e12 644   d
  $ hg manifest --debug --rev 'desc("b-1")' | grep '644   d'
  01c2f5eabdc4ce2bdee42b5f86311955e6c8f573 644   d
  $ hg debugindex d
     rev linkrev nodeid       p1           p2
       0       2 01c2f5eabdc4 000000000000 000000000000
       1      10 b004912a8510 000000000000 000000000000
       2      15 0bb5445dc4d0 01c2f5eabdc4 b004912a8510
       3      22 c72365ee036f 000000000000 000000000000
       4      23 863d9bc49190 01c2f5eabdc4 c72365ee036f
       5      25 7bded9d9da1f 01c2f5eabdc4 000000000000
       6      26 f04cac32d703 b004912a8510 7bded9d9da1f
       7      27 d7a5eafb9322 7bded9d9da1f b004912a8510

(This `hg log` output if wrong, since no merge actually happened).

  $ hg log -Gfr 'desc("mBDm-0")' d
  o    15 mBDm-0 simple merge - one way]
  |\
  o :  14 d-2 re-add d]
  :/
  o  2 i-2: c -move-> d]
  |
  o  1 i-1: a -move-> c]
  |
  o  0 i-0 initial commit: a b h]
  

This `hg log` output is correct

  $ hg log -Gfr 'desc("mDBm-0")' d
  o  14 d-2 re-add d]
  |
  ~

  $ hg status --copies --rev 'desc("i-0")' --rev 'desc("mBDm-0")'
  M b
  A d
    a
  R a
  $ hg status --copies --rev 'desc("i-0")' --rev 'desc("mDBm-0")'
  M b
  A d
  R a

Comparing with a merge with colliding rename
--------------------------------------------

- the "e-" branch renaming b to f (through 'g')
- the "a-" branch renaming d to f (through e)

  $ hg manifest --debug --rev 'desc("mAEm-0")' | grep '644   f'
  eb806e34ef6be4c264effd5933d31004ad15a793 644   f
  $ hg manifest --debug --rev 'desc("mEAm-0")' | grep '644   f'
  eb806e34ef6be4c264effd5933d31004ad15a793 644   f
  $ hg manifest --debug --rev 'desc("a-2")' | grep '644   f'
  0dd616bc7ab1a111921d95d76f69cda5c2ac539c 644   f
  $ hg manifest --debug --rev 'desc("e-2")' | grep '644   f'
  6da5a2eecb9c833f830b67a4972366d49a9a142c 644   f
  $ hg debugindex f
     rev linkrev nodeid       p1           p2
       0       4 0dd616bc7ab1 000000000000 000000000000
       1      18 6da5a2eecb9c 000000000000 000000000000
       2      19 eb806e34ef6b 0dd616bc7ab1 6da5a2eecb9c
  $ hg status --copies --rev 'desc("a-2")' --rev 'desc("mAEm-0")'
  M f
  R b
  $ hg status --copies --rev 'desc("a-2")' --rev 'desc("mEAm-0")'
  M f
  R b
  $ hg status --copies --rev 'desc("e-2")' --rev 'desc("mAEm-0")'
  M f
  R d
  $ hg status --copies --rev 'desc("e-2")' --rev 'desc("mEAm-0")'
  M f
  R d
  $ hg status --copies --rev 'desc("i-2")' --rev 'desc("a-2")'
  A f
    d
  R d
  $ hg status --copies --rev 'desc("i-2")' --rev 'desc("e-2")'
  A f
    b
  R b
  $ hg status --copies --rev 'desc("i-2")' --rev 'desc("mAEm-0")'
  A f
    d
  R b
  R d
  $ hg status --copies --rev 'desc("i-2")' --rev 'desc("mEAm-0")'
  A f
    d
  R b
  R d
  $ hg status --copies --rev 'desc("i-0")' --rev 'desc("mAEm-0")'
  A f
    a
  R a
  R b
  $ hg status --copies --rev 'desc("i-0")' --rev 'desc("mEAm-0")'
  A f
    a
  R a
  R b

Merge:
- one with change to an unrelated file (b)
- one overwriting a file (d) with a rename (from h to i to d)

The overwriting should take over. However, the behavior is currently buggy

  $ hg status --copies --rev 'desc("i-0")' --rev 'desc("mBFm-0")'
  M b
  A d
    a (true !)
    h (false !)
  R a
  R h
  $ hg status --copies --rev 'desc("i-0")' --rev 'desc("mFBm-0")'
  M b
  A d
    h
  R a
  R h
  $ hg status --copies --rev 'desc("b-1")' --rev 'desc("mBFm-0")'
  M d
  R h
  $ hg status --copies --rev 'desc("f-2")' --rev 'desc("mBFm-0")'
  M b
  M d
  $ hg status --copies --rev 'desc("f-1")' --rev 'desc("mBFm-0")'
  M b
  M d
  R i
  $ hg status --copies --rev 'desc("b-1")' --rev 'desc("mFBm-0")'
  M d
  R h
  $ hg status --copies --rev 'desc("f-2")' --rev 'desc("mFBm-0")'
  M b
  $ hg status --copies --rev 'desc("f-1")' --rev 'desc("mFBm-0")'
  M b
  M d
  R i

The following graphlog is wrong, the "a -> c -> d" chain was overwritten and should not appear.

  $ hg log -Gfr 'desc("mBFm-0")' d
  o    23 mBFm-0 simple merge - one way]
  |\
  o :  22 f-2: rename i -> d]
  | :
  o :  21 f-1: rename h -> i]
  :/
  o  2 i-2: c -move-> d]
  |
  o  1 i-1: a -move-> c]
  |
  o  0 i-0 initial commit: a b h]
  

The following output is correct.

  $ hg log -Gfr 'desc("mFBm-0")' d
  o  22 f-2: rename i -> d]
  |
  o  21 f-1: rename h -> i]
  :
  o  0 i-0 initial commit: a b h]
  

Merge:
- one with change to a file
- one deleting and recreating the file

Unlike in the 'BD/DB' cases, an actuall merge happened here. So we should
consider history and rename on both branch of the merge.

  $ hg status --copies --rev 'desc("i-0")' --rev 'desc("mDGm-0")'
  A d
    a
  R a
  $ hg status --copies --rev 'desc("i-0")' --rev 'desc("mGDm-0")'
  A d
    a
  R a
  $ hg status --copies --rev 'desc("d-2")' --rev 'desc("mDGm-0")'
  M d
  $ hg status --copies --rev 'desc("d-2")' --rev 'desc("mGDm-0")'
  M d
  $ hg status --copies --rev 'desc("g-1")' --rev 'desc("mDGm-0")'
  M d
  $ hg status --copies --rev 'desc("g-1")' --rev 'desc("mGDm-0")'
  M d

  $ hg log -Gfr 'desc("mDGm-0")' d
  o    26 mDGm-0 simple merge - one way]
  |\
  | o  25 g-1: update d]
  | |
  o |  14 d-2 re-add d]
  |/
  o  2 i-2: c -move-> d]
  |
  o  1 i-1: a -move-> c]
  |
  o  0 i-0 initial commit: a b h]
  


  $ hg log -Gfr 'desc("mDGm-0")' d
  o    26 mDGm-0 simple merge - one way]
  |\
  | o  25 g-1: update d]
  | |
  o |  14 d-2 re-add d]
  |/
  o  2 i-2: c -move-> d]
  |
  o  1 i-1: a -move-> c]
  |
  o  0 i-0 initial commit: a b h]