Defeating Git Rigour Fatigue with Jujutsu

defeating git rigour fatigue with jujutsu

When developing a large feature, writing Good Commits is hard.

And by Good Commits, I mean something like:

define types

add DB functions

server CRUD

client API

client UI

This allows reviewers to step through your pull request in small bites, with each set of changes scoped to a single aspect of the feature.

So, naturally, here's what I do instead:

define types

add DB functions

WIP test code

server CRUD

client API and UI

fix DB function

fix UI bug

refactor CRUD

fix another UI bug

Latter commits overwrite work that was done in earlier commits and the story breaks.⚖️

Jujutsu makes it easier to hop around commits and iterate quickly on compartmentalized changesets, but it's still effortful and I get averse.🤖

jj absorb helps somewhat, as does jj squash -i, but they both have their downsides:

• absorb assigns the changes based on whichever previous commit most recently touched those files, which sometimes doesn't actually correspond to which commit should ownthese particular changes. - squash can get you stuck in merge conflict hell if your boundaries aren't extremely clean.

So here's a solution to this problem of "git rigour fatigue" that I've come up with.

For this example, let's represent commits visually. Imagine red represents changes to the type definitions, blue to the UI and so on:

Mayhem. Our first commit is a mix of red and blue. We touch red in multiple places!

To fix this, let's create our ideal commit history first, using jj new -B messy-first -m 'red'

Then we can do the rest. (I switch to jj new -A red -m 'blue' at this point)

Then we squash all the commits with actual changes in them into one with jj squash --from messy-first..messy-last --into messy-first

Then we use jj squash -i --from messy-first --into red and pick out the red changes, putting them into the red box:

And so on:

Eventually everything's in the right place and the "everything commit" is empty.

For large features, I find this workflow far easier than having to maintain strict git rigour for the lifecycle of the feature's development. It's easier to make improvised commits with temp debugging state in them and tidy it all up in one sweep at the end.

preemptions:

• I don't have a good name for this technique. "Doing Commits Like A Big Pile Of Laundry", perhaps?

• This is different from (and, imo, superior to) jj split:

• With split, if I miss a hunk that should have been in red, I have to split again and squash.

• This technique more easily allows sorting the easiest hunks at the beginning without worrying about how it will effect the commit sequencing.

• This reason why doing it all at the end is (often) better than using jj squash -i as you go is because the final state of the everything commit is guaranteed to not have any conflicts. Creating a new "fix red and green" commit and interactively squashing that into your red and green commits might break your blue commit if it happens to touch one of the affected files.

• A downside to this technique is that there's no guarantee that every commit will compile, which might be a dealbreaker.