cli: diff: add --exclude flag

[bryceberger]

First contribution, please let me know if this should be an issue / something else first.

Often, while iterating, I end up with a state where I've updated some dependencies (cargo update, etc) and some code. I want to inspect the diff, but jj diff (and jj show, etc) only accept an allowlist. This works ok when all the relevant changes are in a common directory, but is annoying when working in multiple (such as with workspaces).

This adds an --exclude flag to jj diff, which does what it says on the tin. jj diff -x Cargo.lock

Potential pitfalls: jj diff -x *.lock may not work as expected, as it could shell expand to something like jj diff -x Cargo.lock flake.lock, which would exclude Cargo.lock but include flake.lock. Unsure if this motivates a section in the docs.

Checklist

If applicable:

• I have updated CHANGELOG.md
• I have updated the documentation (README.md, docs/, demos/)

[yuja]

I'm not sure if we want to add --exclude in addition to PATH patterns. Is it super inconvenient to specify '~Cargo.lock'?

[ilyagr]

Another possible approach for this would be to have a default-diff-filepattern config.

As I wrote this, I also realized you might be able to instead do

[aliases]
# "diffc" stands for "clean diff" in my mind, there might be better names
diffc = ["diff", "~root-file:Cargo.lock"]

I also ran into this problem, and I think it's worth addressing, but I'm not sure which way is best. (If the alias approach is good enough, which I'm not at all sure about, it could just be a documentation fix maybe)

One downside of the alias approach is that I already have a jj difft and jj delta aliases to pass the diff to difftastic/delta. It'd be annoying to create a "clean diff" variant for each alias.

[bryceberger]

I'm not sure if we want to add --exclude in addition to PATH patterns. Is it super inconvenient to specify '~Cargo.lock'?

No, it's not, just didn't realize that was an option, whoops.

Another possible approach for this would be to have a default-diff-filepattern config.

It would (probably) be a more involved change, but if this route is taken it would be nice to have something like the template system. jj diff -P no_nix to expand to jj diff '~root-path:(flake.lock | flake.nix)'

Regardless, my immediate use case is already solved by ~patterns. Should I close this?

[ilyagr]

[fileset-aliases] sound like an interesting idea to me.