Add support for Svelte.

[umanghome]

Add support for Svelte.

Checklist:

• I am associating a language with a new file extension.

  • The new extension is used in hundreds of repositories on GitHub.com
    • Search results for each extension:
      • https://github.com/search?utf8=%E2%9C%93&type=Code&ref=searchresults&q=extension%3AFOOBAR+KEYWORDS+NOT+nothack
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • [URL to each sample source, if applicable]
    • Sample license(s):
  • I have included a change to the heuristics to distinguish my language from others using the same extension.

• I am adding a new language.

  • The extension of the new language is used in hundreds of repositories on GitHub.com.
    • Search results for each extension:
      • https://github.com/search?q=extension%3Asvelte+export+default+NOT+nothack&type=Code
  • I have included a real-world usage sample for all extensions added in this PR:
    • Sample source(s):
      • Form.svelte
    • Sample license(s):
  • I have included a syntax highlighting grammar: https://github-lightshow.herokuapp.com/?utf8=%E2%9C%93&scope=from-url&grammar_format=auto&grammar_url=https%3A%2F%2Fraw.githubusercontent.com%2Fumanghome%2Fsvelte-atom%2Fmaster%2Fgrammars%2Fsvelte.json&grammar_text=&code_source=from-url&code_url=https%3A%2F%2Fraw.githubusercontent.com%2Fumanghome%2Flinguist%2Fsvelte%2Fsamples%2FSvelte%2FCatList.svelte&code=
  • I have updated the heuristics to distinguish my language from others using the same extension.

• I am fixing a misclassified language

  • I have included a new sample for the misclassified language:
    • Sample source(s):
      • [URL to each sample source, if applicable]
    • Sample license(s):
  • I have included a change to the heuristics to distinguish my language from others using the same extension.

• I am changing the source of a syntax highlighting grammar

  • Old: https://github-lightshow.herokuapp.com/
  • New: https://github-lightshow.herokuapp.com/

• I am updating a grammar submodule

• I am adding new or changing current functionality

  • I have added or updated the tests for the new or changed functionality.

[pchaigno]

Thanks for submitting the pull request!

Could you please update the template with the required information (the search query for in-the-wild usage, information on added samples, and the link to Lightshow showing the grammar in action)?

[umanghome]

@pchaigno Done.

[Rich-Harris]

Svelte creator here, via Twitter. Amazing work Umang, thank you!

I noticed that the sample file is using the old Svelte 1 template syntax (e.g. double {{curlies}}) — is that intentional? Relatedly, we created a separate project to maintain the Svelte 2 syntax called HTMLx (the intention being that other frameworks are free to adopt it without having to invent their own syntax). Eventually our recommendation will be that people use the .htmlx file extension. Is it possible to support .htmlx here alongside .svelte?

[umanghome]

@Rich-Harris Didn't notice the example was written in an older version. I picked up a file from an example on GitHub because the Svelte code that I write for work is confidential. I will pick up an updated sample and update the repository.

I can add .htmlx too, but the usage doesn't seem to be very much yet. I took a look at the README and it seems like it uses the same Grammar as Svelte does. In which case, it would make more sense to add support for HTMLx syntax rather than Svelte syntax as the base, and then let Svelte inherit this base.

[Rich-Harris]

Yeah, usage will be effectively zero for now since we haven't promoted the extension at all (because of the lack of linguist support, which this PR solves!) — we generally just go with good old .html, which gets you 90% of the way there. I spot-checked a few existing uses of .htmlx (without restricting it to files that also include export default) and it seems that in most cases it's temporary renaming of files (i.e. people adding an 'x' as an alternative to e.g. 'file.OLD.html')

[umanghome]

@Rich-Harris Would you agree on keeping HTMLx as the base syntax and then inheriting Svelte syntax support from it for the sole purpose of syntax highlighting?

[Rich-Harris]

That makes sense to me, yes

[umanghome]

I'm keeping .htmlx another extension for Svelte as of now. We can move it later to its own language once it gains enough traction.

[umanghome]

@pchaigno Are there any guidelines on selecting a color for newly added languages?

[pchaigno]

I've left a few comments below that should help you address the Travis CI build failures.
Could you also check whether these files are Svelte files too? They looks like plain HTML files to me.

[pchaigno]

I counted 117 repositories by 102 users from the search query you provided. That a bit low considering our usual requirement of hundreds of repositories, but it's unlikely we'll get any conflicts in the future given the extension. @lildude What do you think?

[lildude]

Unfortunately, that usage is not high enough for inclusion right now, it's barely over a hundred let alone hundreds.

[pchaigno]

This needs to be source.svelte.

[pchaigno]

You don't need to set a color since it has a group; it will automatically take the parent's color.

[pchaigno]

Items in languages.yml should be alphabetically sorted, with uppercase letters first.

[Rich-Harris]

They're not Svelte files — my hypothesis is:

in most cases it's temporary renaming of files (i.e. people adding an 'x' as an alternative to e.g. 'file.OLD.html'

Happily, HTML files highlighted as HTMLx will be identical except in some unusual edge cases, so the worst that will result from the false positive is that those files will now be highlighted as HTML instead of not at all.

At present, the vast majority of Svelte files are written with an .html extension. There are enough .svelte files to show up in search, but ideally we'd want to use the .htmlx extension instead — we've just held off doing that someone got around to sending a PR to linguist (and that someone turned out to be @umanghome!).

[pchaigno]

They're not Svelte files — my hypothesis is:

in most cases it's temporary renaming of files (i.e. people adding an 'x' as an alternative to e.g. 'file.OLD.html'

Sorry, I missed that before.

Happily, HTML files highlighted as HTMLx will be identical except in some unusual edge cases, so the worst that will result from the false positive is that those files will now be highlighted as HTML instead of not at all.

Usage is way too low to add them now. Maybe we could add .htmlx as a HTML extension though (in a separate pull request)? I counted 351 repositories by 327 users so usage is fine.

If you think usage of .htmlx for Svelte files will grow rapidly, I can add the extension to #4219.

we've just held off doing that someone got around to sending a PR to linguist.

With this pull request, you'll be able to switch on syntax highlighting of .htmlx Svelte files on a per-repository basis, using Linguist overrides.

[Rich-Harris]

Ah, nice, I didn't know about overrides.

Maybe we could add .htmlx as a HTML extension though (in a separate pull request)?

That would make it practical to start using that extension, which could hopefully solve the chicken-and-egg problem we have at the moment, so yes — that sounds like an excellent starting point. Could you point us in the right direction please?

I expect usage will grow in time, yes — if you could add it to #4219 that'd be great. Thank you!

[umanghome]

If we are going to add support for .htmlx, I would recommend making .svelte one of the file extensions for the HTMLx language. I would be happy to work on adding HTMLx in a different PR if we decide to close this one and go with HTMLx instead.

[pchaigno]

Could you point us in the right direction please?

You can follow the contribution guidelines for that.

If we are going to add support for .htmlx, I would recommend making .svelte one of the file extensions for the HTMLx language. I would be happy to work on adding HTMLx in a different PR if we decide to close this one and go with HTMLx instead.

I wasn't suggesting to add HTMLx as a language, just .htmlx as a new HTML extension.

if you could add it to #4219 that'd be great.

Done.

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