Add sourceURL to inline script and style tags

[sirreal]

Trac ticket: https://core.trac.wordpress.org/ticket/63887

Script and style tags can add a sourceURL comment to name them for developer tools. This is similar to sourceMappingURL that are often used with JavaScript compilers. They are described in this specification.

Messages and styles that come from inline scripts and styles are often difficult to understand and debug because they typically point to part of the current URL, like (index):1530 or ?p=1535:1530. These point to a line number in the page HTML and are confusing and inconsistent across pages.

Inline scripts and styles can provide a sourceURL to provide a consistent name and simplify debugging, for example //# sourceURL=example-js-after. It seems to be supported in Chrome, Firefox, and Edge at this time. Safari does not appear to support it.

Some examples from developer tools in Chrome:

Inline styles before

body { (index):475
    background: red !important;
}

After

body { example-inline-css:2
    background: red !important;
}

---

Inline scripts before

Uncaught Error: Oh no!
    at (index):1401:7

After

example-js-after:2 Uncaught Error: Oh no!
    at example-js-after:2:7

---

This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

[github-actions]

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[github-actions]

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Props jonsurrell, swissspidy, alshakero, westonruter.

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[sirreal]

Inline scripts and styles include a sourceURL that matches the ID attributes used in their tags, for example:

• scripthandle-js-before
• scripthandle-js-after
• stylehandle-inline-css

wp_localize_script() is not handled in the first version of this PR. If desired, that can likely be added.

@alshakero brought this to my attention. I know @jsnajdr, @sgomes, and @youknowriad also expressed interest.

[swissspidy]

Great idea!

I saw this feature recently too and thought it would be perfect for core, so thanks for adding this!

[sirreal]

Shall I see about handling wp_localize_script() as well?

[sirreal]

I pushed a change to add sourceURL to scripts produced by wp_localize_script() as well.

[alshakero]

I tested it and tried my best to break it (new lines, */ in handle and weird characters in handle), and it worked like a charm!

TIL: New lines will make it through when used in a script handle. But the rawurlencode took care of these.

[westonruter]

I saw this feature recently too and thought it would be perfect for core, so thanks for adding this!

Me too! I had this on my list to follow up on. Specifically via: https://x.com/csswizardry/status/1954863359695720623

[westonruter]

What about prefixing the sourceURL with inline: as suggested in that tweet?

[sirreal]

What about prefixing the sourceURL with inline:…

I don't feel strongly, but after reflecting I'm inclined to add it. I don't believe there are technical reasons to use a specific name or format, this should be what's easiest for people to identify. I do think there's value in using the same name as the ID of the script or style element, but that would be fine with or without the inline: prefix.

Right now the source URLs look like this:

• handle-js-before
• handle-js-after
• handle-js-extra
• handle-inline-css

With the prefix and no other changes they'd be:

• inline:handle-js-before
• inline:handle-js-after
• inline:handle-js-extra
• inline:handle-inline-css

It seems slightly redundant in the style case inline:handle-inline-css, but in general this adds nice clarity about the provenance.

[github-actions]

A commit was made that fixes the Trac ticket referenced in the description of this pull request.

SVN changeset: 60685
GitHub commit: bc10e6b

This PR will be closed, but please confirm the accuracy of this and reopen if there is more work to be done.

[csswizardry]

Just a quick heads up, you may want to be aware of this. Especially at WP’s scale: https://x.com/csswizardry/status/1955262508178043002

[sirreal]

Thanks, it sounds like we now have a technical reason to avoid the inline: prefix 🙂 I'll do some investigation and prepare a change to remove it.

From the linked tweet:

inline: breaks LoAF attribution so a pattern like //# sourceURL=foo.inline.js is probably better.

Referring to Long Animation Frames API.

[sirreal]

#9655 removes the inline: prefix.