tests/test-histedit-revspec.t

rebase: do not invent successor to skipped changeset

When rebase results in an empty a changeset it is "skipped" and no related
changeset is created at all. When we added obsolescence support to rebase (in
fc2a6114f0a0) it seemed a good idea to use its parent successor as the
successors for such dropped changesets. (see old version of the altered test).
This option was chosen because it seems a good way to hint about were the
dropped changeset "intended" to be. Such hint would have been used by automatic
evolution mechanism to rebase potential unstable children.

However, field testing of this version are not conclusive. It very often leads
to the creation of (totally unfounded) evolution divergence. This changeset
changes this behavior and mark skipped changesets as pruned (obsolete without
successors). This prevents the issue and seems semantically better probably a
win for obsolescence reading tool.

See example bellow for details:

User Babar has five changesets of interest:
- O, its current base of development.
- U, the new upstream
- A and C, some development changesets
- B another development changeset independent from A

    O - A - B - C
      \
        U

Babar decides that B is more critical than the A and C and rebase it first

  $ hg rebase --rev B --dest U

B is now obsolete (in lower case bellow). Rebase result, B', is its
successors.(note, C is unstable)

    O - A - b - C
      \
        U - B'

Babar is now done with B', and want to rebase the rest of its history:

  $ hg rebase --source A --dest B'


hg rebase process A, B and C. B is skipped as all its changes are already contained
in B'.

    O - U - B' - A' - C'

Babar have the expected result graph wise, obsolescence marker are as follow:

    B -> B' (from first rebase)
    A -> A' (from second rebase)
    C -> C' (from second rebase)
    B -> ?? (from second rebase)

Before this changeset, the last marker is `B -> A'`. This cause two issues:

- This is semantically wrong. B have nothing to do with A'
- B has now two successors sets: (B',) and (A',). We detect a divergent
  rewriting. The B' and A' are reported as "divergent" to Babar, confusion
  ensues. In addition such divergent situation (divergent changeset are children
  to each other) is tricky to solve.

With this changeset the last marker is `B -> ø`:

- This is semantically better.
- B has a single successors set (B',)

This scenario is added to the tests suite.

This test requires parentrevspec support in revsets, so check for that
and skip the test if we're on an unusual hg that supports .t tests but
not parentrevspec.
  $ python -c 'from mercurial import revset ; revset.methods["parentpost"]' || exit 80

Enable extensions used by this test.
  $ cat >>$HGRCPATH <<EOF
  > [extensions]
  > graphlog=
  > histedit=
  > EOF

Repo setup.
  $ hg init foo
  $ cd foo
  $ echo alpha >> alpha
  $ hg addr
  adding alpha
  $ hg ci -m one
  $ echo alpha >> alpha
  $ hg ci -m two
  $ echo alpha >> alpha
  $ hg ci -m three
  $ echo alpha >> alpha
  $ hg ci -m four
  $ echo alpha >> alpha
  $ hg ci -m five

  $ hg log --style compact --graph
  @  4[tip]   08d98a8350f3   1970-01-01 00:00 +0000   test
  |    five
  |
  o  3   c8e68270e35a   1970-01-01 00:00 +0000   test
  |    four
  |
  o  2   eb57da33312f   1970-01-01 00:00 +0000   test
  |    three
  |
  o  1   579e40513370   1970-01-01 00:00 +0000   test
  |    two
  |
  o  0   6058cbb6cfd7   1970-01-01 00:00 +0000   test
       one
  

Run a dummy edit to make sure we get tip^^ correctly via revsingle.
  $ HGEDITOR=cat hg histedit "tip^^"
  pick eb57da33312f 2 three
  pick c8e68270e35a 3 four
  pick 08d98a8350f3 4 five
  
  # Edit history between eb57da33312f and 08d98a8350f3
  #
  # Commands:
  #  p, pick = use commit
  #  e, edit = use commit, but stop for amending
  #  f, fold = use commit, but fold into previous commit (combines N and N-1)
  #  d, drop = remove commit from history
  #  m, mess = edit message without changing commit content
  #
  0 files updated, 0 files merged, 0 files removed, 0 files unresolved

Run on a revision not ancestors of the current working directory.

  $ hg up 2
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg histedit -r 4
  nothing to edit
  [1]