tests/test-single-head-obsolescence-named-branch-A3.t

rust-index: using the `hg::index::Index` in ancestors iterator and lazy set

Since there is no Rust implementation for REVLOGV2/CHANGELOGv2, we declare
them to be incompatible with Rust, hence indexes in these formats will use
the implementations from Python `mercurial.ancestor`. If this is an unacceptable
performance hit for current users of these formats, we can later on add Rust
implementations based on the C index for them or implement these formats for
the Rust indexes.

Among the challenges that we had to meet, we wanted to avoid taking the GIL each
time the inner (vcsgraph) iterator has to call the parents function. This would probably
still be acceptable in terms of performance with `AncestorsIterator`, but not with
`LazyAncestors` nor for the upcoming change in `MissingAncestors`.

Hence we enclose the reference to the index in a `PySharedRef`, leading to more
rigourous checking of mutations, which does pass now that there no logically immutable
methods of `hg::index::Index` that take a mutable reference as input.

=========================================
Testing single head enforcement: Case A-3
=========================================

A repository is set to only accept a single head per name (typically named
branch). However, obsolete changesets can make this enforcement more
complicated, because they can be kept visible by other changeset on other
branch.

This case is part of a series of tests checking this behavior.

Category A: Involving obsolescence
TestCase 3: Full superseding of a branch interleaved with another

.. old-state:
..
.. * 2 changesets on branch default
.. * 2 changesets on branch Z interleaved with the other
..
.. new-state:
..
.. * 2 changesets on branch Z at the same location
.. * 2 changesets on branch default superseding the other ones
..
.. expected-result:
..
.. * only one head detected
..
.. graph-summary:
..
..   D ●      (branch Z)
..     |
..   C ø⇠◔ C'
..     | |
..   B ● |    (branch Z)
..     | |
..   A ø⇠◔ A'
..     |/
..     ●

  $ . $TESTDIR/testlib/push-checkheads-util.sh

  $ cat >> $HGRCPATH << EOF
  > [command-templates]
  > log = "{node|short} [{branch}] ({phase}): {desc}\n"
  > EOF

Test setup
----------

  $ mkdir A3
  $ cd A3
  $ setuprepos single-head
  creating basic server and client repo
  updating to branch default
  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ cd client
  $ hg branch Z
  marked working directory as branch Z
  (branches are permanent and global, did you want a bookmark?)
  $ mkcommit B0
  $ hg branch default --force
  marked working directory as branch default
  $ mkcommit C0
  created new head
  $ hg branch Z --force
  marked working directory as branch Z
  $ mkcommit D0
  created new head
  $ hg push --new-branch
  pushing to $TESTTMP/A3/server
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 3 changesets with 3 changes to 3 files
  $ hg up 0
  0 files updated, 0 files merged, 4 files removed, 0 files unresolved
  $ mkcommit A1
  created new head
  $ mkcommit C1
  $ hg debugobsolete `getid "desc(A0)"` `getid "desc(A1)"`
  1 new obsolescence markers
  obsoleted 1 changesets
  3 new orphan changesets
  $ hg debugobsolete `getid "desc(C0)"` `getid "desc(C1)"`
  1 new obsolescence markers
  obsoleted 1 changesets
  $ hg heads
  0c76bc104656 [default] (draft): C1
  78578c4306ce [Z] (draft): D0
  $ hg log -G --hidden
  @  0c76bc104656 [default] (draft): C1
  |
  o  f6082bc4ffef [default] (draft): A1
  |
  | *  78578c4306ce [Z] (draft): D0
  | |
  | x  afc55ba2ce61 [default] (draft): C0
  | |
  | *  93e5c1321ece [Z] (draft): B0
  | |
  | x  8aaa48160adc [default] (draft): A0
  |/
  o  1e4be0697311 [default] (public): root
  

Actual testing
--------------

  $ hg push -r 'desc("C1")'
  pushing to $TESTTMP/A3/server
  searching for changes
  adding changesets
  adding manifests
  adding file changes
  added 2 changesets with 2 changes to 2 files (+1 heads)
  2 new obsolescence markers
  obsoleted 2 changesets
  2 new orphan changesets