Bundled Svelte grammar has cyclical includes — syntect consumers spin forever #4081

Title: Bundled Svelte grammar has cyclical includes — syntect consumers spin forever

The Svelte syntax this crate bundles (02_Extra/Svelte, the
corneliusio/svelte-sublime submodule) contains cyclical includes:

style-common  → style-lang-attribute → style-lang-decider-type → style-common
style-common  → style-lang-attribute → style-lang-decider-lang → style-common
script-common → script-lang-attribute → script-lang-decider-lang → script-common
style-lang-decider-type → script-common → script-lang-attribute → …

Sublime Text / VS Code tolerate these (their include walk is cycle-safe), but
syntect's is not: MatchIter::next pushes the target context with no
"already on the stack?" check, so the context stack grows without bound and
parse_line never returns.

Concretely: highlighting a five-byte line — /** — inside a Svelte diff
pins a core at 100 % forever. html / javascript / typescript / vue parse
the same input in < 10 ms; only svelte loops. It is neither line length nor
regex backtracking (capping oniguruma's retry_limit_in_match to 20 000 still
spins).

This is filed here (rather than only upstream) because two-face ships the
grammar, so every two-face user who highlights a Svelte file hits it. A
second, non-consuming-set loop in parse_line compounds it.

• Upstream fix (both halves needed): Bugfix: Parser can enter infinite loop on cyclical references trishume/syntect#709
  — unmerged since 2026-09-25.
• I ported Point to delta in usage-with-git section of README #709 onto syntect 5.3.0 and confirmed the wedge goes away (Svelte
  diff parses in ≤ 20 ms).

Happy to send a PR here too if you'd rather adjust the bundled grammar (or pin
a fixed syntect) — just say which you prefer.