view CONTRIBUTING @ 32009:c6cb21ddf74a

checkheads: upgrade the obsolescence postprocessing logic (issue4354)

The previous logic had many shortcoming (eg: looking at the head only, not
handling prune, etc...), the new logic use a more robust approach:

For each head, we check if after the push all changesets exclusive to this heads
will be obsolete. If they are, the branch considered be "replaced".

To check if a changeset will be obsolete, we simply checks:

* the changeset phase

* the existence of a marker relevant to the "pushed set" that affects the
  changesets..

This fixes two major issues of the previous algorithm:

* branch partially rewritten (eg: head but not root) are no longer detected as
  replaced,

* Prune are now properly handled.

(This implementation was introduction in the evolve extension, version 6.0.0.)

This new algorithm has an extended number of tests, a basic one is provided
in this patch. The others will be introduced in their own changeset for clarity.

In addition, we stop trying to process heads unknown locally, we do not have
enough data to take an informed decision so we should stop pretending we do.
This reflect a test that is now update.

Our full contribution guidelines are in our wiki, please see:

https://www.mercurial-scm.org/wiki/ContributingChanges

If you just want a checklist to follow, you can go straight to

https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist

If you can't run the entire testsuite for some reason (it can be
difficult on Windows), please at least run `contrib/check-code.py` on
any files you've modified and run `python contrib/check-commit` on any
commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).