Mercurial disallow pushing multiple heads

So why are multiple heads evil, and why do we want to stop hg from pushing them to another repo. Well, usually multiple heads are caused by failed merge attempts (avoiding merges). Pushing multiple heads in this situation will postpone the need of merging (it will be needed eventually), or make somebody else merge the heads. If a programmer intends to make a new head in the first place - he is likely to create a new branch.

Another reason do want to push multiple head changesets are auto build/test frameworks. If the execute hg incoming and suddenly see 3 heads instead of one. Surely they'll fail to carry on their routine.

I believe I've mentioned something about mercurial hooks and some of their applications. These hooks may be used to disallow pushing changesets with more than one head. We don't have to implement this hook by ourselves, a good implementation is available at hg.pythong.org.

mkdir ~/hooks && cd ~/hooks
wget http://hg.python.org/hooks/archive/fc6022656a7b.tar.gz -O hooks.tar.gz
tar zxf hooks.tar.gz && mv hooks-fc6022656a7b/* .

Now we need to edit, the ~/.hgrc file.

[hooks]
pretxnchangegroup.checkheads = python:/home/kr/hooks/checkheads.py:hook


Let's see how it works:

~ $ ~/prj/python/bw $ hg push
pushing to /home/kr/repos/bw
searching for changes
abort: push creates new remote head 4ffea01f3220!
(did you forget to merge? use push -f to force)

This was to be expected, by default mercurial required the -f switch to push a changeset containing multiple heads.

~ $ hg push -f
pushing to /home/kr/repos/bw
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files (+1 heads)
* You are trying to create new head(s) on 'default'!
* Please run "hg pull" and then merge at least two of:
* c96b37d67e47, 4ffea01f3220
transaction abort!
rollback completed
abort: pretxnchangegroup.checkheads hook failed

This hook gives +10 to keeping your repo tidy!

Cheers!
KR

P.S.
There are some more hooks in the downloaded archive, feel free to check them out.