Script Modules API: Backport - Add import map polyfill

[cbravobernal]

Syncs the changes from WordPress/gutenberg#58263 to core.
Adds a polyfill to make import maps compatible with Safari old versions (under 15).

Trac ticket: https://core.trac.wordpress.org/ticket/60348

Screenshots:

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[github-actions]

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[luisherranz]

I requested changes in the Gutenberg's PR but the same should be applied here:

• Script Modules API: Add import map polyfill gutenberg#58263 (review)

[cbravobernal]

Done in 7dd5f5a

[gziolo]

Code-wise it seems to be ready to go. Do we have unit tests covering other polyfills? We could verify if the script prints when there are items in the import map.

[cbravobernal]

Code-wise it seems to be ready to go. Do we have unit tests covering other polyfills? We could verify if the script prints when there are items in the import map.

I will take a look at it, if not, I will check if can add unit tests to cover them.

[sirreal]

Sharing notes on this change that I co-authored with @c4rl0sbr4v0.

First, a minor change. We use RegExp.test() instead of String.match(). We don't care about the result of matching, we want to know "does this match," so RegExp.test() (with its boolean result) is ideal.

Second, and more important. The expression was not specific enough and was matching JavaScript source files that were, themselves, looking for sourcemap comments. In this PR is was matching this line from es-module-shims:

  const sourceMapURLCommentPrefix = '\n//# sourceMappingURL=';

We change to better match a source map comment by anchoring the expression to the start of the line and matching the comment opening //# . This fixes the false positives and allows us to remove several files from the ignore list.

[gziolo]

Everything looks good from my perspective. Thank you for all the iterations! @sirreal, is it ready to commit?

[sirreal]

I've only reviewed the small bit I was involved with around the build (verify that sourcemap URLs are not included in compiled JS filed).

Looks good! 👍

[gziolo]

What would be the case when $wp_scripts is not set? I'm asking because I don't see it guarded anywhere else in the codebase?

I see some ! empty( $wp_scripts ) checks.

[gziolo]

Committed with https://core.trac.wordpress.org/changeset/57492.