http://mercurial.selenic.com/bts/issue522

In the merge below, the file "foo" has the same contents in both

parents, but if we look at the file-level history, we'll notice that

the version in p1 is an ancestor of the version in p2. This test makes

sure that we'll use the version from p2 in the manifest of the merge

revision.

  $ hg init

  $ echo foo > foo

  $ hg ci -qAm 'add foo'

  $ echo bar >> foo

  $ hg ci -m 'change foo'

  $ hg backout -r tip -m 'backout changed foo'

  reverting foo

  changeset 2:4d9e78aaceee backs out changeset 1:b515023e500e

  $ hg up -C 0

  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ touch bar

  $ hg ci -qAm 'add bar'

  $ hg merge --debug

    searching for copies back to rev 1

    unmatched files in local:

     bar

  resolving manifests

   branchmerge: True, force: False, partial: False

   ancestor: bbd179dfa0a7, local: 71766447bdbb+, remote: 4d9e78aaceee

   foo: remote is newer -> g

  getting foo

  updating: foo 1/1 files (100.00%)

  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  (branch merge, don't forget to commit)

  $ hg debugstate | grep foo

  m   0         -2 unset               foo

  $ hg st -A foo

  M foo

  $ hg ci -m 'merge'

  $ hg manifest --debug | grep foo

  c6fc755d7e68f49f880599da29f15add41f42f5a 644   foo

  $ hg debugindex foo

     rev    offset  length  ..... linkrev nodeid       p1           p2 (re)

       0         0       5  .....       0 2ed2a3912a0b 000000000000 000000000000 (re)

       1         5       9  .....       1 6f4310b00b9a 2ed2a3912a0b 000000000000 (re)

       2        14       5  .....       2 c6fc755d7e68 6f4310b00b9a 000000000000 (re)