Revert "Change grammar source for Svelte"

[lildude]

Reverts #5963

This broke the syntax highlighting between <(script|style|template)> tags due to a really old limitation in the old prettylights highlighting engine which won't be fixed.

See #6164 for more details.

This can be reverted back to the sveltejs/svelte-atom grammar once it has been updated to address this limitation or a production-ready tree-sitter grammar becomes available.

This PR will be merged early next week (w/c 28 Nov 2022) and a patch release made, unless the sveltejs/svelte-atom grammar is updated by then, in which case I'll pull the latest version of that grammar.

Fixes #6180

[Alhadis]

due to a really old limitation in the old prettylights highlighting engine

Could you elaborate on the specifics of said limitation? This is relevant because I still use Atom for writing, previewing and testing grammars, and I need to know of any discrepancies between it and GitHub/PrettyLights.

[lildude]

See #6164 (comment)

[Alhadis]

The problem is it doesn't expand scope matches and instead treats the $1 in places like this literally:

Oh, that. I always assumed that was an intentional optimisation due to the rarity of meaningful scopes getting captured by a grammar. It's bitten me several times when abusing injections (most recently in language-mermaid).

(Sorry for the noise…)

[lildude]

Oh, that. I always assumed that was an intentional optimisation due to the rarity of meaningful scopes getting captured by a grammar.

It's certainly possible. I can't find any explanation of why this wasn't implemented other than a "Expand?" comment in the code and the author left GitHub a long time ago - I doubt they could remember why they wrote that over 8 years ago too 😁.

[lildude]

No updates have been made to the sveltejs/svelte-atom grammar so I'm going to go ahead and merge this.