Jetpack_PostImages::from_attachment: Prevent warning when $thumb_post_data cannot be found

[mreishus]

Fixes warnings like:

[25-Jan-2024 21:08:38 UTC] Warning: Attempt to read property "guid" on null in (...)/class.jetpack-post-images.php on line 342

Proposed changes:

• When Jetpack_PostImages::from_attachment runs, it tries to get data from a thumbnail post:

			if ( ! is_array( $img_src ) ) {
				// If wp_get_attachment_image_src returns false but we know that there should be an image that could be used.
				// we try a bit harder and user the data that we have.
				$thumb_post_data = get_post( $thumb );
				$img_src         = array( $thumb_post_data->guid, $meta['width'], $meta['height'] );
			}

get_post() can return null, so sometimes $thumb_post_data->guid is null and generates a warning.

However, the 0th (first) entry of $img_src isn't always used. The code block after it is:

			if ( defined( 'IS_WPCOM' ) && IS_WPCOM ) {
				$featured_image = get_post_meta( $post->ID, '_jetpack_featured_image' );
				if ( $featured_image ) {
					$url = $featured_image[0];
				} else {
					$url = $img_src[0];
				}
			} else {
				$url = $img_src[0];
			}
			$images = array(
				array( // Other methods below all return an array of arrays.
					'type'       => 'image',
					'from'       => 'thumbnail',
					'src'        => $url,
					'src_width'  => $img_src[1],
					'src_height' => $img_src[2],
					'href'       => get_permalink( $thumb ),
					'alt_text'   => self::get_alt_text( $thumb ),
				),
			);

Note that at least one of the code paths uses $featured_image[0] instead of $img_src[0]. In the real world case that I tried of seeing the warning generated, that was the case. So my solution is only to silence the warning by using $thumb_post_data->guid ?? null instead of $thumb_post_data->guid. That should keep the behavior the same, but stop the warning from happening.

As far as I know, there is no unwanted behavior or bugs happening here, only a warning.

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

Does this pull request change what data or activity we track or use?

Testing instructions:

• See D135990-code for a testing helper and directions

[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WordPress.com Simple site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin, and enable the update/post-images-2 branch.

• To test on Simple, run the following command on your sandbox:

  bin/jetpack-downloader test jetpack update/post-images-2
  

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[github-actions]

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[anomiex]

Not sure what's going on to make it not get a post there. But this shouldn't make it any worse, whatever it is.