How to abandon a hg merge?

BTW: if you just revert the merge you did and 3 is not your revision number you can do this:

hg update -C -r .

You can discard uncommitted changes with the -C (or --clean) flag:

hg update -C -r 3

BEWARE: Everything that was not committed will be gone!

After that you should probably use some kind of code formatter tool to do the entire operation, or at least some find and replace with regular expressions. Something as simple as replacing what matches ^____ (use 4 spaces instead of underscores) with __ (2 spaces), repeated a few times (unless you have insanely some nested code) should work.

To undo an uncommitted merge, use

hg update --clean

which will check out a clean copy of the original merge parent, losing all changes.