How to squash two non-consecutive commits in Mercurial

The problem

Suppose you want to combine two commits in Mercurial. However, they are not consecutive. What to do? histedit to the rescue!

Suppose hg log shows that your last 4 revisions are the following:

1
2
3
4

3: more stuff on Y
2: stuff on X
1: stuff on Y
0: stuff on Z

And suppose you want to squash what you commited on Y into a single revision, like this:

1
2
3

2: stuff + more stuff on Y
1: stuff on X
0: stuff on Z

Reorder revisions

The first step is to reorder the revision history in order to make the revisions to be squashed become consecutive (stuff on Y and more stuff on Y):

1

hg histedit

Select the revision you want to move (1: stuff on Y) and move it down (press capital J). Why down? Well, hg log is reverse chronological so the latest revision on top, while hg histedit is chronological so the latest revision is at the bottom. Confusing, I know. Just commit (press c) and now your hg log should show the reordered revisions:

1
2
3
4

3: more stuff on Y
2: stuff on Y
1: stuff on X
0: stuff on Z

Squash the two commits

Since the revisions on Y are now consecutive, we can finally “fold” them (they might have called it “squash”, it would have been more intuitive). However, we must tell Mercurial from which revision to start: we want revision number 2 in the log above, since it is the one on top of which the other one will be “folded”:

1

hg histedit 2

Then select revision 3 (more stuff on Y) and select “fold” (press f). Commit (press c) and edit the commit message (e.g., stuff + more stuff on Y) and you should now have the hg log that you wanted all along:

1
2
3

2: stuff + more stuff on Y
1: stuff on X
0: stuff on Z