Force HTML5 script theme support when printing JSON script

[westonruter]

Summary

When a theme doesn't declare theme support for HTML5 scripts, the JSON script is currently output with some XHTML compatibility wrappers:

<script type="speculationrules">
/* <![CDATA[ */
{"prerender":[{"source":"document","where":{"and":[{"href_matches":"\/*"},{"not":{"href_matches":["\/wp-login.php","\/wp-admin\/*"]}},{"not":{"selector_matches":".no-prerender"}}]},"eagerness":"moderate"}]}
/* ]]> */
</script>

This breaks the parsing of the JSON. The /* <![CDATA[ */ and /* ]]> */ need to be omitted from JSON output.

Relevant technical choices

This needs to be fixed in core (ticket and PR pending), but a quick workaround is to temporarily override the $_wp_theme_features global with the theme support added.

Update: See core ticket: https://core.trac.wordpress.org/ticket/60320

Checklist

• PR has either [Focus] or Infrastructure label.
• PR has a [Type] label.
• PR has a milestone or the no milestone label.

[felixarntz]

@westonruter Can you open a Trac ticket for this? I think we should prioritize this, and it would be great to link to that in a code comment here.

If the fix in core is straightforward (which I would expect it to be), then we can maybe ship this in 6.5 already and thus limit or remove this workaround sooner than later.

[westonruter]

Can you open a Trac ticket for this? I think we should prioritize this, and it would be great to link to that in a code comment here.

Yes, I started doing that right after opening this PR (ref: "(ticket and PR pending)").

Here it is: https://core.trac.wordpress.org/ticket/56313

Oops. I mean here: https://core.trac.wordpress.org/ticket/60320

[joemcgill]

Looks good to me. One question about the tests, but pre-approving for merge.

[joemcgill]

I don't remember if theme support get reset between tests. Any chance of this causing side effects for other tests?

[westonruter]

Right. Good point. Fixed in a1037f8