Amp-wp: CSS Parser does not preserve styles used inside templates script[type=text/plain]

[spasibych]

Bug Description

The plugin implements the removal of unused CSS rules on the page. This works well for all page content, including <template type="amp-mustache">...</template>, but does not work with <script type="text/plain" template="amp-mustache">...</script>.

Expected Behaviour

Preserve CSS rules for elements inside <script type="text/plain" template="amp-mustache">...</script>.

Steps to reproduce

1. Add code to AMP page:

<style>
    h2.one { color: green }
    h2.two { color: red }
</style>
<template type="amp-mustache">
    <h2 class="one">One</h2>
</template>
<script type="text/plain" template="amp-mustache">
    <h2 class="two">Two</h2>
</script>

1. View the resulting source code for an AMP page.
2. See content <style amp-custom>...</style> in page head where there is a rule h2.one{color:green} but there is no rule h2.two{color:red}.

Additional context

• WordPress version: 5.3.2
• Plugin version: 1.4.2
• AMP plugin template mode: Website; Standard; Serve all templates as AMP regardless of what is being queried.
• PHP version: 7.3.11

Acceptance criteria

Implementation brief

QA testing instructions

Demo

Changelog entry

[westonruter]

I believe this may be resolved by fixing #4254.

[spasibych]

@westonruter thanks!

This is especially important if full support of <!--{{#foo}}--> is not implemented (issue #26656).

[schlessera]

I believe this may be resolved by fixing #4254.

Just verified that this is indeed fixed via the PR that @kienstra did for #4254 :

I'll add a "Fixes #4276" to that PR.

[spasibych]

Bug is present with plugin version 1.5 (1.5.0 and 1.5.1).

[westonruter]

Bizzare. We did fix this. But I'm not seeing it now.

[westonruter]

@spasibych Here’s a 1.5.2-RC1 pre-release build with the fix for you to test: amp.zip (v1.5.2-RC1-20200403T193031Z-3102c5dea)

[westonruter]

We've just published the 1.5.2 release to WordPress.org: https://wordpress.org/plugins/amp/

You can update now via the WordPress admin.

Release notes: https://github.com/ampproject/amp-wp/releases/tag/1.5.2

[spasibych]

@westonruter now everything is fine, thank you very much!