Fix: PDF thumbnails to WEBP/AVIF

[AhmarZaidi]

Summary

This PR adds support for generating Modern Format (webp/aif) image thumbnails from PDF files.

Fixes #1766

Relevant technical choices

• Added application/pdf mimetype to the default transforms list and use get_attached_file() function for getting the original pdf file path if mime type is application/pdf to bypass $image_path = wp_get_original_image_path( $attachment_id );
• Add unit tests for web uploads helper functions to check if 'application/pdf' is included in the MIME transforms array.

Screen records

Screen.Recording.2025-02-12.at.8.48.56.AM.mov

[AhmarZaidi]

As mentioned in the issue comment, the solution doesn't seem work when we test it on the dev environment run using npm run wp-env start and shows security policy error:

WP_Error Object
(
    [errors] => Array
    (
        [invalid_image] => Array
        (
            [0] => attempt to perform an operation not allowed by the security policy `PDF' @ error/constitute.c/IsCoderAuthorized/426
        )
    )

    [error_data] => Array
    (
        [invalid_image] => /var/www/html/wp-content/uploads/2025/02/test.pdf
    )

    [additional_data:protected] => Array ()
)

This appears to be an issue with ImageMagick policy used in the docker WordPress environment. Solutions suggest changing the ImageMagick policy

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 66.72%. Comparing base (42bd7a8) to head (7b3facd).

Additional details and impacted files

@@            Coverage Diff             @@
##            trunk    #1868      +/-   ##
==========================================
+ Coverage   66.70%   66.72%   +0.01%     
==========================================
  Files          88       88              
  Lines        7029     7032       +3     
==========================================
+ Hits         4689     4692       +3     
  Misses       2340     2340              

Flag	Coverage Δ
multisite	66.72% <100.00%> (+0.01%)	⬆️
single	37.22% <100.00%> (+0.02%)	⬆️

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[westonruter]

Minor point: This is easier to read and it would facilitate ensuring test coverage is present for both code paths. Also, in the future maybe there will be more such special cases.

Suggested change

	$image_path = 'application/pdf' !== get_post_mime_type( $attachment_id ) ? wp_get_original_image_path( $attachment_id ) : get_attached_file( $attachment_id );
	if ( 'application/pdf' === get_post_mime_type( $attachment_id ) {
	$image_path = get_attached_file( $attachment_id );
	} else {
	$image_path = wp_get_original_image_path( $attachment_id ); }

[AhmarZaidi]

I was thinking something like this:

$image_path = wp_attachment_is_image( $attachment_id ) ? wp_get_original_image_path( $attachment_id ) : get_attached_file( $attachment_id );

This way we can use wp_get_original_image_path() only when attatchment is an image and in all other cases we can use get_attached_file ()

This is also more in accordance with latest suggestions made on the issue thread: #1766 (comment)

[westonruter]

Let's still avoid the ternary for readability and to ensure we have code coverage for both conditions:

Suggested change

	$image_path = wp_attachment_is_image( $attachment_id ) ? wp_get_original_image_path( $attachment_id ) : get_attached_file( $attachment_id );
	if ( wp_attachment_is_image( $attachment_id ) ) {
	$image_path = wp_get_original_image_path( $attachment_id );
	} else {
	$image_path = get_attached_file( $attachment_id );
	}