For the impatient

Ok, here is what you have to do on your Ubuntu box:

$ sudo apt-get install rcs
$ vim ~/.hgrc

… and put the following lines somewhere into your ~/.hgrc

[merge-tools]
merge.priority = 100

The full story

As an active user of the Mercurial version control system I’ve been struggling for quite some time with its merging facilities. Actually all wanted was Subversion alike behavior: once the conflict happens special text markers are placed into the conflicting source files and one has to resolve these conflicts manually using one’s favorite text editor(vim in my case).

There is a terse mention about the required behavior in the official Mercurial book(it boils down to setting HGMERGE env. variable as follows: $ export HGMERGE=merge). However the Mercurial book recommends using one of the GUI merge tool instead(kdiff3, meld, etc) and I simply can’t stand GUI stuff for this purpose. I recall one day I had to merge branches using ssh, now how would I do it with GUI?

I tried setting HGMERGE env. variable but it didn’t work since merge wasn’t actually installed on my Ubuntu box but for some reason I didn’t get it(probably because of some obscure error message) and I simply started using a GUI merge tool… I felt really unhappy and had to live with it for quite some time until one day when a colleague of mine told me to install the rcs package which actually contained the merge tool!

It also makes sense to use [merge-tools] section of the .hgrc configuration file instead of HGMERGE env. variable but, of course, YMMV.

Update: the same trick is possible on Windows as well! All you have to do is to install GNU rcs binaries into your Path. However, there is a problem with diff3 binary bundled with GNU rcs - it crashes. You have to install diff3 from somewhere else, for example from nixtools. In order to save your time I’m attaching a zip file containing rcs with working diff3.GNU rcs(with working diff3)