Adding an amp-access-scroll element to the page fails to add required scripts

[westonruter]

Bug Description

As reported on support forum, when adding amp-access for Scroll to the page, the amp-access-scroll component script fail to be added automatically.

For example, given this code:

add_action('wp_head', function () {
	?>
	<script id="amp-access" type="application/json">
		{
			"vendor": "scroll",
			"namespace": "scroll"
		}
	</script>
	<?php
});

add_action( 'wp_footer', function () {
	?>
	<section amp-access="NOT scroll.scroll">
		ad goes here
	</section>
	<?php
} );

The result is only that the main amp-access script is added to the page:

<script async custom-element="amp-access" src="https://cdn.ampproject.org/v0/amp-access-0.1.js"></script>

Expected Behaviour

Expected the amp-access-scroll to also be added:

<script async custom-element="amp-access-scroll" src="https://cdn.ampproject.org/v0/amp-access-scroll-0.1.js"></script>

Steps to reproduce

1. Put the above PHP code in a plugin.
2. View an AMP page in Standard, Transitional, or non-legacy Reader mode.

Workaround

There is a workaround and that is to manually add the amp-access-scroll component to the page. This can either be done by enqueueing the script:

wp_enqueue_script( 'amp-access-scroll' );

Also, the script can just be manually printed out anywhere in the page:

<script async custom-element="amp-access-scroll" src="https://cdn.ampproject.org/v0/amp-access-scroll-0.1.js"></script>

The AMP plugin will automatically move it to the head.

Something to investigate is why the amp-access-scroll script is not removed automatically given that it was not added automatically in the first place. The AMP plugin is supposed to be removing components automatically which are not needed in the document.

---

Do not alter or remove anything below. The following sections will be managed by moderators only.

Acceptance criteria

Implementation brief

QA testing instructions

Demo

Changelog entry

[westonruter]

This should rather be solved in the Optimizer with the AutoExtension transformer logic.

[westonruter]

I just tried pasting the above snippets into the AMP playground and the only script which was automatically added was:

<script async custom-element="amp-access" src="https://cdn.ampproject.org/v0/amp-access-0.1.js"></script>

And the document remains valid even though it lacks the amp-access-scroll extension.

[schlessera]

Opened an issue here: ampproject/amphtml#33801

[schlessera]

Fixed as a work-around via #297