Delta for diffs

[robinst]

I'm used to https://github.com/dandavison/delta for looking at diffs, and was wondering how to set it up with jj. I started with just setting the tool:

[ui.diff]
tool = "delta"

That results in this:

$ jj diff

Δ var/folders/jl/2lwh7cg533j2f03mnjk7vfv80000gn/T/jj-diff-plVolZ/left/docs/index.md ⟶   var/folders/jl/2lwh7cg533j2f03mnjk7vfv80000gn/T/jj-diff-plVolZ/right/docs/index.md
──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────

─────┐
• 1: │
─────┘
# Jujutsu—a version control system
# Jujutsu—a version control system test

## Welcome to `jj`'s documentation website!

Warning: Tool exited with exit status: 1 (run with --debug to see the exact invocation)

Note the very long left/right path. It can be improved like this:

[ui.diff]
tool = ["delta", "$left", "$right", "--file-transformation", "s|.*/jj-diff-[^/]*/[^/]*/||"]

$ jj diff

Δ docs/index.md ⟶   docs/index.md
────────────────────────────────────────────────────────────────────────────────

─────┐
• 1: │
─────┘
# Jujutsu—a version control system
# Jujutsu—a version control system test

## Welcome to `jj`'s documentation website!

Warning: Tool exited with exit status: 1 (run with --debug to see the exact invocation)

What I haven't found is how to silence the warning at the end:

Warning: Tool exited with exit status: 1 (run with --debug to see the exact invocation)

Has anyone figured out how? Any other tips?

[robinst]

Shortly after posting this, I found the section about pagers in the docs, and this makes jj diff work nicely:

[ui]
pager = "delta"

[ui.diff]
format = "git"

I'll leave this post up because I couldn't find how to configure delta before (and I searched through discussions).

One problem that's left is with the above config, jj log -p doesn't use the pager, but that seems to be a known issue:

• FR: jj log respect the diff pager config #4142

[david-crespo]

Loving delta as my pager, but I was annoyed that jj log output would disappear on quit — I often use the log to find a change ID to plug into a subsequent command.

It turns out that by default, jj uses less -FRX as its pager, and the X means "leave the last view as output in the terminal when you quit". But delta, when it calls less internally, must not pass -X because it doesn't do that.

To use jj’s default less command while still using delta you can do:

pager = ["delta", "--pager", "less -FRX"]

I don’t love this either because when I look at a diff, I don’t usually want it to stick around. I only want this behavior when I’m looking at the log, and even then, I might not want it all the time. It turns out you can put the following in ~/.lesskey to make Q keep the output on quit while q does the regular quit:

Q toggle-option -!^Predraw-on-quit\nq

Then pager = "delta" works just fine. Note that for this to work on macOS, I had to brew install less to get a newer version than the super old one that comes built in.

[rwjblue]

Thanks for that @david-crespo! It got me thinking about the newish --scope features. I've just updated my config to only use delta as a pager for jj diff (I think this support landed in ~ 0.26). That looks like:

[[--scope]]
--when.commands = ["diff"]

[--scope.ui]
# https://github.com/jj-vcs/jj/blob/v0.25.0/docs/config.md#processing-contents-to-be-paged
pager = "delta"
# NOTE: this is required when using `delta` as a pager
diff.format = "git"

With this config, jj log contents stay on screen properly! 🎉

---

I was worried that this might break jj log -p formatting (because now log wouldn't be using delta as a pager), but apparently that doesn't work yet anyways (see #4142).

[david-crespo]

Nice. You might also want it for show.

[JacobHayes]

Has anyone been able to get colorMoved[1] working well? It's generated by git, so guessing ui.diff.format = "git" would need to support it or use a different ui.diff.tool. Unfortunately, using delta for ui.diff.tool breaks delta's color theme detection.

1: detect moved code and highlight differently than just add/delete