Diffing custom functions

[kokkonisd]

Thank you for this tool!

I played around with it a bit, and to my surprise, it seems that it's currently not possible to diff the content yielded by custom functions.
I am using typdiff version 0.1.1, installed via cargo install --locked typdiff.
Consider the following 3 files:

config.typ:

#let my-stack(one, two, three) = stack(
    dir: ttb,
    spacing: 1em,
    one,
    two,
    three,
)

old.typ:

#import "config.typ": *

#my-stack("a", "b", "c")

new.typ:

#import "config.typ": *

#my-stack("a", "b", "d")

Then, typdiff yields:

$ typdiff old.typ new.typ
#let diff-added(body) = {
  set text(fill: rgb("#0000ff"))
  underline(body)
}
#let diff-deleted(body) = {
  set text(fill: rgb("#cc0000"))
  strike(body)
}

#import "config.typ": *

// #my-stack("a", "b", "c")

#my-stack("a", "b", "d")

But I would expect this instead:

#let diff-added(body) = {
  set text(fill: rgb("#0000ff"))
  underline(body)
}
#let diff-deleted(body) = {
  set text(fill: rgb("#cc0000"))
  strike(body)
}

#import "config.typ": *

#my-stack("a", "b", {diff-deleted("c"); diff-added("d")})

The latter highlights the difference in the arguments passed to my-stack(), while the former does not.

Is this a feature you plan to support? How hard would it be to implement?

[sou1118]

Thanks for the detailed report and the clear example!

This is definitely something I want to support. I'm currently working on argument-level diffing for FuncCall blocks so that typdiff would output something like:

#my-stack("a", "b", {diff-deleted["c"]; diff-added["d"]})

I've been prototyping this locally, and the basic idea works. However, it turned out to be trickier than I initially expected — there are some subtle edge cases around embedding code-mode expressions inside diff markers in a way that Typst can still compile correctly.

I'd like to get this right, so it might take some time. Thanks for your patience!