tests/test-copies-chain-merge.t

copy-tracing: test case where a merge reverted a file deletion

This case is currently broken for commit centric copy tracing. So we add an
official case for it with a note about it being broken.

Fixing it will requires multiples change in code related to merge, commit and
copy tracing, so we introduce it beforehand for simplicity.

Also, I have been sitting on this test for 3 months so I would rather have it
upstream.

#testcases filelog compatibility sidedata

=====================================================
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

#if compatibility
  $ cat >> $HGRCPATH << EOF
  > [experimental]
  > copies.read-from = compatibility
  > EOF
#endif

#if sidedata
  $ cat >> $HGRCPATH << EOF
  > [format]
  > exp-use-side-data = yes
  > exp-use-copies-side-data-changeset = yes
  > EOF
#endif


  $ 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
  

Create a branch that delete a file previous renamed

  $ hg up 'desc("i-2")'
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg rm d
  $ hg ci -m 'c-1 delete d'
  created new head
  $ hg log -G --rev '::.'
  @  6 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
  

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

  $ hg up 'desc("i-2")'
  1 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 '::.'
  @  8 d-2 re-add d
  |
  o  7 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
  

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

  $ hg up 'desc("i-2")'
  1 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 '::.'
  @  10 e-2 g -move-> f
  |
  o  9 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
  

merging with unrelated change does not interfere with the renames
---------------------------------------------------------------

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

  $ hg up 'desc("b-1")'
  1 files updated, 0 files merged, 1 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"))'
  @    12 mABm-0 simple merge - the other way
  |\
  +---o  11 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
  

  $ 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

  $ hg up 'desc("b-1")'
  1 files updated, 0 files merged, 1 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"))'
  @  16 mCBm-1 re-add d
  |
  o    15 mCBm-0 simple merge - the other way
  |\
  | | o  14 mBCm-1 re-add d
  | | |
  +---o  13 mBCm-0 simple merge - one way
  | |/
  | o  6 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
  
- 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 up 'desc("b-1")'
  1 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")'
  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 'mDBm-0 simple merge - the other way'
  created new head
  $ hg log -G --rev '::(desc("mDBm")+desc("mBDm"))'
  @    18 mDBm-0 simple merge - the other way
  |\
  +---o  17 mBDm-0 simple merge - one way
  | |/
  | o  8 d-2 re-add d
  | |
  | o  7 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
  
  $ 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
  $ 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'
  b004912a8510032a0350a74daa2803dadfb00e12 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       8 b004912a8510 000000000000 000000000000

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

  $ hg log -Gfr 'desc("mBDm-0")' d
  o  8 d-2 re-add d
  |
  ~

This `hg log` output is correct

  $ hg log -Gfr 'desc("mDBm-0")' d
  o  8 d-2 re-add d
  |
  ~

  $ hg status --copies --rev 'desc("i-0")' --rev 'desc("mBDm-0")'
  M b
  A d
  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 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  10 e-2 g -move-> f
  | |
  | o  9 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
  
  $ 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      10 6da5a2eecb9c 000000000000 000000000000
       2      19 eb806e34ef6b 0dd616bc7ab1 6da5a2eecb9c

# Here the filelog based implementation is not looking at the rename
# information (because the file exist on both side). However the changelog
# based on works fine. We have different output.

  $ hg status --copies --rev 'desc("a-2")' --rev 'desc("mAEm-0")'
  M f
    b (no-filelog !)
  R b
  $ hg status --copies --rev 'desc("a-2")' --rev 'desc("mEAm-0")'
  M f
    b (no-filelog !)
  R b
  $ hg status --copies --rev 'desc("e-2")' --rev 'desc("mAEm-0")'
  M f
    d (no-filelog !)
  R d
  $ hg status --copies --rev 'desc("e-2")' --rev 'desc("mEAm-0")'
  M f
    d (no-filelog !)
  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

# From here, we run status against revision where both source file exists.
#
# The filelog based implementation picks an arbitrary side based on revision
# numbers. So the same side "wins" whatever the parents order is. This is
# sub-optimal because depending on revision numbers means the result can be
# different from one repository to the next.
#
# The changeset based algorithm use the parent order to break tie on conflicting
# information and will have a different order depending on who is p1 and p2.
# That order is stable accross repositories. (data from p1 prevails)

  $ 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 (filelog !)
    b (no-filelog !)
  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 (filelog !)
    b (no-filelog !)
  R a
  R b


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       8 b004912a8510 000000000000 000000000000
       2      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")'
  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 '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
  
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
    h
    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
    h (no-filelog !)
  R h
  $ hg status --copies --rev 'desc("f-2")' --rev 'desc("mBFm-0")'
  M b
  $ hg status --copies --rev 'desc("f-1")' --rev 'desc("mBFm-0")'
  M b
  M d
    i (no-filelog !)
  R i
  $ hg status --copies --rev 'desc("b-1")' --rev 'desc("mFBm-0")'
  M d
    h (no-filelog !)
  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
    i (no-filelog !)
  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  22 f-2: rename i -> d
  |
  o  21 f-1: rename h -> i
  :
  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 actual merge happened here. So we should
consider history and rename on both branch of the merge.

  $ 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 |  8 d-2 re-add d
  | |
  o |  7 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
  
One side of the merge have a long history with rename. The other side of the
merge point to a new file with a smaller history. Each side is "valid".

(and again the filelog based algorithm only explore one, with a pick based on
revision numbers)

  $ hg status --copies --rev 'desc("i-0")' --rev 'desc("mDGm-0")'
  A d
    a (filelog !)
  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 |  8 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 |  8 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
  


Merge:
- one with change to a file (d)
- one overwriting that file with a rename (from h to i, to d)

This case is similar to BF/FB, but an actual merge happens, so both side of the
history are relevant.

Note:
| In this case, the merge get conflicting information since on one side we have
| "a -> c -> d". and one the other one we have "h -> i -> d".
|
| The current code arbitrarily pick one side

  $ hg up 'desc("f-2")'
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ hg merge 'desc("g-1")' --tool :union
  merging d
  0 files updated, 1 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -m 'mFGm-0 simple merge - one way'
  created new head
  $ hg up 'desc("g-1")'
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg merge 'desc("f-2")' --tool :union
  merging d
  0 files updated, 1 files merged, 1 files removed, 0 files unresolved
  (branch merge, don't forget to commit)
  $ hg ci -m 'mGFm-0 simple merge - the other way'
  created new head
  $ hg log -G --rev '::(desc("mGFm")+desc("mFGm"))'
  @    29 mGFm-0 simple merge - the other way
  |\
  +---o  28 mFGm-0 simple merge - one way
  | |/
  | o  25 g-1: update d
  | |
  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
  
  $ hg status --copies --rev 'desc("i-0")' --rev 'desc("mFGm-0")'
  A d
    h (no-filelog !)
    a (filelog !)
  R a
  R h
  $ hg status --copies --rev 'desc("i-0")' --rev 'desc("mGFm-0")'
  A d
    a
  R a
  R h
  $ hg status --copies --rev 'desc("f-2")' --rev 'desc("mFGm-0")'
  M d
  $ hg status --copies --rev 'desc("f-2")' --rev 'desc("mGFm-0")'
  M d
  $ hg status --copies --rev 'desc("f-1")' --rev 'desc("mFGm-0")'
  M d
    i (no-filelog !)
  R i
  $ hg status --copies --rev 'desc("f-1")' --rev 'desc("mGFm-0")'
  M d
    i (no-filelog !)
  R i
  $ hg status --copies --rev 'desc("g-1")' --rev 'desc("mFGm-0")'
  M d
    h (no-filelog !)
  R h
  $ hg status --copies --rev 'desc("g-1")' --rev 'desc("mGFm-0")'
  M d
    h (no-filelog !)
  R h

  $ hg log -Gfr 'desc("mFGm-0")' d
  o    28 mFGm-0 simple merge - one way
  |\
  | o  25 g-1: update d
  | |
  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
  

  $ hg log -Gfr 'desc("mGFm-0")' d
  @    29 mGFm-0 simple merge - the other way
  |\
  | o  25 g-1: update d
  | |
  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
  


Comparing with merging with a deletion (and keeping the file)
-------------------------------------------------------------

Merge:
- one removing a file (d)
- one updating that file
- the merge keep the modified version of the file (canceling the delete)

In this case, the file keep on living after the merge. So we should not drop its
copy tracing chain.

  $ hg up 'desc("c-1")'
  1 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ hg merge 'desc("g-1")'
  file 'd' was deleted in local [working copy] but was modified in other [merge rev].
  You can use (c)hanged version, leave (d)eleted, or leave (u)nresolved.
  What do you want to do? u
  0 files updated, 0 files merged, 0 files removed, 1 files unresolved
  use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
  [1]
  $ hg resolve -t :other d
  (no more unresolved files)
  $ hg ci -m "mCGm-0"
  created new head

  $ hg up 'desc("g-1")'
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg merge 'desc("c-1")'
  file 'd' was deleted in other [merge rev] but was modified in local [working copy].
  You can use (c)hanged version, (d)elete, or leave (u)nresolved.
  What do you want to do? u
  0 files updated, 0 files merged, 0 files removed, 1 files unresolved
  use 'hg resolve' to retry unresolved file merges or 'hg merge --abort' to abandon
  [1]
  $ hg resolve -t :local d
  (no more unresolved files)
  $ hg ci -m "mGCm-0"
  created new head

  $ hg log -G --rev '::(desc("mCGm")+desc("mGCm"))'
  @    31 mGCm-0
  |\
  +---o  30 mCGm-0
  | |/
  | o  25 g-1: update d
  | |
  o |  6 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
  

BROKEN: 'a' should be the the source of 'd' in the changeset centric algorithm too

  $ hg status --copies --rev 'desc("i-0")' --rev 'desc("mCGm-0")'
  A d
    a (filelog !)
  R a
  $ hg status --copies --rev 'desc("i-0")' --rev 'desc("mGCm-0")'
  A d
    a (filelog !)
  R a
  $ hg status --copies --rev 'desc("c-1")' --rev 'desc("mCGm-0")'
  A d
  $ hg status --copies --rev 'desc("c-1")' --rev 'desc("mGCm-0")'
  A d
  $ hg status --copies --rev 'desc("g-1")' --rev 'desc("mCGm-0")'
  $ hg status --copies --rev 'desc("g-1")' --rev 'desc("mGCm-0")'


Comparing with merge restoring an untouched deleted file
--------------------------------------------------------

Merge:
- one removing a file (d)
- one leaving the file untouched
- the merge actively restore the file to the same content.

In this case, the file keep on living after the merge. So we should not drop its
copy tracing chain.

  $ hg up 'desc("c-1")'
  0 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 revert --rev 'desc("b-1")' d
  $ hg ci -m "mCB-revert-m-0"
  created new head

  $ hg up 'desc("b-1")'
  0 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 revert --rev 'desc("b-1")' d
  $ hg ci -m "mBC-revert-m-0"
  created new head

  $ hg log -G --rev '::(desc("mCB-revert-m")+desc("mBC-revert-m"))'
  @    33 mBC-revert-m-0
  |\
  +---o  32 mCB-revert-m-0
  | |/
  | o  6 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
  

BROKEN: 'a' should be the the source of 'd' in the changeset centric algorithm too

  $ hg status --copies --rev 'desc("i-0")' --rev 'desc("mCB-revert-m-0")'
  M b
  A d
    a (filelog !)
  R a
  $ hg status --copies --rev 'desc("i-0")' --rev 'desc("mBC-revert-m-0")'
  M b
  A d
    a (filelog !)
  R a
  $ hg status --copies --rev 'desc("c-1")' --rev 'desc("mCB-revert-m-0")'
  M b
  A d
  $ hg status --copies --rev 'desc("c-1")' --rev 'desc("mBC-revert-m-0")'
  M b
  A d
  $ hg status --copies --rev 'desc("b-1")' --rev 'desc("mCB-revert-m-0")'
  $ hg status --copies --rev 'desc("b-1")' --rev 'desc("mBC-revert-m-0")'