Fix arrow highlight 14299

[michaelwalshe]

Description

Update arrow-light.theme to highlight BuiltIn and Extension styles rather than setting as null, applying highlighting more similarly to arrow-dark.theme and other themes. Chosen the same colour as Function style to keep arrow-light fairly minimal.

Fixes #14299

Examples

Example quarto file below which has a few different languages and some builtin & extension style types.

---
highlight-style: arrow
theme:
  light: flatly
  dark: darkly
format:
  html:
    embed-resources: true
---

```typst
#let config = (
  debug: none,
  width: auto,
  visible: true,
)

#let show-box(width: auto, border: none, fill: false) = {
  let has-border = border != none
  box(width: width, stroke: if has-border { border } else { none })
}
```

```python
import re
from statistics import mean

x = abs(-5)

y = dict(
    z = 5,
    b = 1
)

z = mean((1,2,3))

s = re.compile(r"\w{2}\d+[[:upper:]]*")
```

```terraform
locals {
  name    = trimprefix(upper("  hello-world  "), " ")
  offset  = abs(-42)
  items   = sort(["banana", "apple", "cherry"])
  joined  = join(", ", local.items)
  hash    = substr(sha256("my-id"), 0, 8)
}
```

Resulting html under old and new versions of highlighting:

test_old.html

test_new.html

Screenshot samples of differences:

Old:

New:

[cderv]

Thanks for the fix and the clear before/after comparison.

I tested the change locally with the repro from the issue (plus axe-core via axe: true) — no new contrast violations, and the BuiltIn/Extension tokens now render distinctly from surrounding code as expected. The Function color choice keeps arrow-light's palette minimal and reuses an already a11y-vetted value, which I prefer over a larger redesign.

Contributor agreement

It looks like our PR template was removed from the PR description. One of the items it covers — also documented in CONTRIBUTING.md — is the contributor agreement. Since this is your first PR here, could you confirm you've signed an individual or corporate contributor agreement (sent to contribute@posit.co)? That's required for changes beyond small typos. If you'd rather not go through that process, no worries — let me know and I can re-implement the change on our side, crediting you in the commit.

(Note: the PDF links in our CONTRIBUTING docs are currently broken on Posit's side — I'll follow up separately to fix those. If you need the documents, let me know and I can send them to you by email.)

A note on theme parity (not blocking)

I considered whether to mirror arrow-dark's mapping (BuiltIn = Char color, Extension = Variable color + bold) more literally. In arrow-dark those are semantically distinct, but in arrow-light Variable is #111111 — effectively "don't highlight" — so mirroring would leave Extension visually indistinct from normal text. Your Function-based choice is the pragmatic fix within arrow-light's existing design. Broader light/dark consistency we can revisit separately.

[michaelwalshe]

Thanks for taking a look.

Sorry for removing the template - did work through the checklist but removed as thought it was noise. On the contributor link - both of those are broken and 404 for me, so can't sign them (and not really a fan of signing an agreement for a contribution to an MIT licensed repo).

Happy for you to re-implement the change and commit yourself :)

[cderv]

(and not really a fan of signing an agreement for a contribution to an MIT licensed repo)

yeah I am looking into that. I agree. This is leftover from when quarto was GPL at the beginning but we never removed. I'll ask around.

And I discovered broken links today - Posit has a new website and those files were lost in migration it seems.

Thanks again for your contribution.