I noticed that from a point in tortoisehg’s history, extdiff was broken on default installs. It just kept popping up “No visual tool has been configured”. This happened even if one defined ‘meld’ or ‘/usr/bin/meld‘ in hgtk userconfig. Today I got in the mood to debug this. After some hacking and hg bisects I found the answer. Where? In the hgtk manual (“use the manual, Luke!”).

You’ll need to edit your ~/.hgrc by hand and add the following in it:

[extdiff]
cmd.meld = meld
opts.meld =

Now, the ‘meld’ option will be available in hgtk’s userconfig tool and will be used for visual diff operations.