Image block: set img_srcset to avoid PHP undefined var warning

[ramonjd]

What? How?

Found while testing #73157

Initialize $img_srcset to false before the conditional block, matching the pattern used for other variables and the return value of wp_get_attachment_image_srcset() when no attachment ID is available.

Why?

When "Enlarge on click" (lightbox) is enabled via global styles, a PHP warning occurs for image blocks in post lists (e.g., on the home page's query block).

Warning: Undefined variable $img_srcset in /var/www/html/wp-content/plugins/gutenberg/build/scripts/block-library/image.php on line 224

In block_core_image_render_lightbox(), $img_srcset is only set inside if ( isset( $block['attrs']['id'] ) ), but it's used later in wp_interactivity_state() regardless of whether the condition was met.

Unlike $img_width and $img_height, which are initialized to 'none' before the conditional, $img_srcset wasn't initialized.

Testing Instructions

Setup:

1. Create a new post/page
2. Insert an Image block and save.

Enable the lightbox in global styles:

1. Go to Appearance → Editor → Styles
2. Navigate to Blocks → Image
3. Enable "Enlarge on click" in global settings
4. Save changes

Visit the homepage or a template with a posts query block.

Ensure the following error is not logged:

[andrewserong]

Good catch!

I could reproduce by testing an Image block using "Insert from URL", too, where no id gets set.

Looks like the issue was introduced when #61107 landed, and I see from that PR that the $img_srcset value winds up being handled via lightboxSrcset in getImageSrcset here where falsy values will be treated as an empty string. So code-wise it's looking good, and in practice this is testing well for me with the lightbox working as expected on the site frontend.

LGTM 👍

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Co-authored-by: ramonjd <ramonopoly@git.wordpress.org>
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[t-hamano]

I think this warning is new in 6.9. Is it worth backporting to 6.9 RC3?

cc @Takshil-Kunadia @westonruter @luisherranz

[westonruter]

@t-hamano This issue appears to have been introduced as part of #61107 and released with Gutenberg 22.1. Is that included in 6.9?

[t-hamano]

@westonruter Sorry, I was mistaken. Gutenberg 22.1 is NOT to be included in WordPress 6.9, so there is no need to backport this PR.