Block gallery styles erroneously get output as separate style from amp-custom in Classic mode

[westonruter]

Reported in https://wordpress.org/support/topic/amp-custom-is-missing-in-the-class-amp-gallery-embed-php/

On a site with Classic mode, the template is currently generating the following invalid markup in the head when a gallery is used:

<style amp-custom>
...
</style>
<style>
	.wp-block-gallery.is-cropped .blocks-gallery-item amp-img > img {
		object-fit: cover;
	}
</style>

This seems to be due to the use of wp_print_styles action introduced in #1627 via 6b7d305.

[westonruter]

This seems to be a plugin compatibility problem with NextGEN Gallery. In particular, there is a conflict between how that plugin (for some reason) does output buffering in its resource manger component. Here is a workaround compatibility plugin: https://gist.github.com/westonruter/99b1ca0d593f44888401a396d991e3a6

See also https://wordpress.org/support/topic/amp-custom-is-missing-in-the-class-amp-gallery-embed-php/#post-11092401

[jackmcconnell]

I am also experiencing this but am not using NextGen gallery. I'm using a custom theme and have disabled all functions to try and prevent the issue from occurring but it still appears. This leads me to believe that a core WordPress function relating to images that is used by the theme may be causing the issue. Additionally, I believe better handling of when this style is output on the page should be added as, whilst using the latest version of WordPress, the whole site is using the Classic Editor plugin and as this related to a Gallery Block in the Block/Gutenberg editor, it shouldn't be being added to the page at all.

[westonruter]

I believe this issue will be made obsolete by #2202 since the entire Reader mode template will be sent through the AMP processor.

Here's a recent development build you can test to confirm: amp.zip (1.5.0-alpha-20200107T191925Z-833fbf594)

[jackmcconnell]

Thanks @westonruter. Have installed and am testing but nothing in between the if (have_posts()) : while (have_posts()) : the_post(); and endwhile; else : endif; is being rendered on the page. Is this expected?

[westonruter]

No, that is not expected.

[jackmcconnell]

@westonruter I appreciate this probably isn't the place for this but when using any custom theme i've tried and using a custom AMP template, nothing is rendered between the if (have_posts()) : while (have_posts()) : the_post(); and endwhile; else : endif; when using Reader mode and only Website and Posts are checked in AMP > General. Reverting back to v1.4.2 renders everything as expected.

[jackmcconnell]

Ok, it seems that using the_content(); outside of the loop when on an AMP template is the fix for now. The loop seems to fail completely in this scenario. Will investigate more if I have the time.

[westonruter]

What template mode are you using? Standard, Transitional, or Reader?

So you have AMP-specific templates in your theme (in an amp/ subdirectory)?

[jackmcconnell]

Reader Mode. I've using the amp_post_template_file filter to set my own template for posts (a modified single.php file).

[westonruter]

Can you share the original single.php file before you made changes to it?

[jackmcconnell]

Sure. See attached.
single.txt

[westonruter]

@jackmcconnell Thanks very much. You identified a bug. I've opened a fix in #4185. In the future you'll be able to use The Loop as normal. Here's a new build to test: #4185 (comment).