Ensure `wp_editor_set_quality` filter consistently passes output mime type

[adamsilverstein]

In https://core.trac.wordpress.org/ticket/53667 we extended the capability of the wp_editor_set_quality filter so that the passed mime_type parameter could be used to set the default image quality per mime type.

Unfortunately, in my testing this filter doesn't quite work correctly: the output mime type (if set with the image_editor_output_formats filter) is not passed consistently to the filter.

I used this ​code in an mu plugin to test the adjusting just WebP output quality filter (and log the passed mime type) with a "real world" test: setting output quality either very high (100) or very low (1) for webp only and comparing the output file size. The filter worked for the -scaled.webp but not the rest of the sub-sizes.

In addition to the filter not passing the correct mimes, we need to expand our testing in test_set_quality_with_image_conversion which continues to pass even though the filter isn't working correctly, possibly because it is only testing a single image generation call, or only testing the results of calling get_quality not the actual quality used.

One test we could add would mimic what I am doing to test this manually: generate all subsizes with the filter in place - applying only to image/webp mime type images - returning first low quality, then high quality, - calling wp_create_image_subsizes with no filter, then each option, then verifying the file sizes are all smaller with the lower quality applied and bigger (than default) with high quality applied.

Note: I assume this is a bug that affected 5.8+ and have marked the ticket as such. I also verified this is still a bug in trunk.

Tests fail currently, demonstrating issue

Trac ticket:

[adamsilverstein]

56442.diff​:

• Add a new test test_quality_with_image_conversion_file_sizes to verify that the wp_editor_set_quality correctly passes the mime type and applies correctly:
  • uses the image_editor_output_format filter to generate both JPEG and WebP sub sizes for a test image (including a -scaled version).
  • sets quality very low for JPEG and very high for WebP and verifies that the file sizes are all larger for the WebP generated files.
• Update WP_Image_Editor::set_quality to set the output type by calling get_output_format.

These tests fail in trunk because the mime type is not set to the output type early enough - the first time it is called for WebP (for each editor initialization), the mime type was set to JPEG even if the eventual output was in WebP. Therefore, certain image sizes were using the JPEG quality setting, not the expected WebP quality setting.

Previous tests for mime type in wp_editor_set_quality weren't catching this because they didn't look at all runs of the filter. The new test looks at all generated sizes.

The fix is a ​single line change to call get_output_format in set_quality. This ensures that $this->output_format is properly set on the next line and the correct mime type is used. After this change, the test passes - the correct mime type is passed to the filter..

Hmm, some other tests fail now because they assert that quality will not be set until save (see test_set_quality_with_image_conversion), I'm going to think and discuss more about the best approach here.

[adamsilverstein]

In 56442.3.diff​

• All tests pass: new tests verify created size is smaller

[adamsilverstein]

56442.4.diff​ refresh against trunk

[adamsilverstein]

@azaozz or @desrosj any feedback here?

[adamsilverstein]

56442.5.diff​ is a refresh against trunk; this should be good to commit, pending review and feedback.

[flixos90]

56442.5.diff​ almost looks good for commit to me, I left feedback in ​https://github.com/WordPress/wordpress-develop/pull/3250.

[adamsilverstein]

56442.6.diff​ addresses the latest feedback on the ticket and is ready for commit

@peterwilsoncc thanks for the review and feedback. I addressed all your points and assuming tests pass this should be ready for commit.

Still manually testing the fix though.

A good way to test this filter is to output WebPs and try setting the quality very high or low, then checking your output files. A filter based on mime type won't work correctly before this fix.

Here are the filters to use:

{{{php
Output WebP.
add_filter( 'image_editor_output_format', function() {

return array(

'image/jpeg' => 'image/webp',

);

});
}}}

{{{php
Filter WebP quality.
add_filter( 'wp_editor_set_quality', function( $quality, $mime_type ) {

if ( 'image/webp' === $mime_type ) {

return 99; Very high quality, files will be very much larger than usual. Alternately, try a very low value.

}
return $quality;

}, 10, 2 );
}}}

[adamsilverstein]

Thanks for the feedback @peterwilsoncc - I have addressed and added some steps for manual testing if you still want to try to do that. I have tested manually and am confident in the fix.

[adamsilverstein]

In 54417:

Media: ensure the wp_editor_set_quality filter consistently passes the correct output mime type.

Ensure that the mime type passed to the wp_editor_set_quality filter is correct when the output format is altered with the image_editor_output_format filter and the image is saved multiple times, for example when generating sub sizes. Previously, the original image mime type was passed instead of the output type after the initial save.

Props flixos90, peterwilsoncc.
Fixes #56442.