Fix background-image styled tag visitor's handling of parsing style without background-image

[westonruter]

In a support forum topic, a user reported Image Prioritizer was causing a warning and fatal error in the Image_Prioritizer_Background_Image_Styled_Tag_Visitor class.

PHP Warning: Undefined array key “background_image” in .../image-prioritizer/class-image-prioritizer-background-image-styled-tag-visitor.php on line 44

PHP Fatal error: Uncaught TypeError: Image_Prioritizer_Tag_Visitor::is_data_url(): Argument #1 ($url) must be of type string, null given, called in .../image-prioritizer/class-image-prioritizer-background-image-styled-tag-visitor.php on line 46 and defined in .../image-prioritizer/class-image-prioritizer-tag-visitor.php:61

Stack trace:
#0 /srv/data/web/vhosts/[domain removed]/htdocs/wp-content/plugins/image-prioritizer/class-image-prioritizer-background-image-styled-tag-visitor.php(46): Image_Prioritizer_Tag_Visitor->is_data_url()
#1 /srv/data/web/vhosts/[domain removed]/htdocs/wp-content/plugins/optimization-detective/optimization.php(183): Image_Prioritizer_Background_Image_Styled_Tag_Visitor->__invoke()
#2 /srv/data/web/vhosts/[domain removed]/htdocs/wp-includes/class-wp-hook.php(324): od_optimize_template_output_buffer()
#3 /srv/data/web/vhosts/[domain removed]/htdocs/wp-includes/plugin.php(205): WP_Hook->apply_filters()
#4 /srv/data/web/vhosts/[domain removed]/htdocs/wp-content/plugins/optimization-detective/optimization.php(44): apply_filters()
#5 [internal function]: {closure}()
#6 /srv/data/web/vhosts/[domain removed]/htdocs/wp-includes/functions.php(5420): ob_end_flush()
#7 /srv/data/web/vhosts/[domain removed]/htdocs/wp-includes/class-wp-hook.php(324): wp_ob_end_flush_all()
#8 /srv/data/web/vhosts/[domain removed]/htdocs/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters()
#9 /srv/data/web/vhosts/[domain removed]/htdocs/wp-includes/plugin.php(517): WP_Hook->do_action()
#10 /srv/data/web/vhosts/[domain removed]/htdocs/wp-includes/load.php(1270): do_action()
#11 [internal function]: shutdown_action_hook()
#12 {main} thrown in /srv/data/web/vhosts/[domain removed]/htdocs/wp-content/plugins/image-prioritizer/class-image-prioritizer-tag-visitor.php on line 61

The issue is faulty logic here:

performance/plugins/image-prioritizer/class-image-prioritizer-background-image-styled-tag-visitor.php

Line 42 in 5a2d306

false !== preg_match( '/background(-image)?\s*:[^;]*?url\(\s*[\'"]?\s*(?<background_image>.+?)\s*[\'"]?\s*\)/', $style, $matches )

Namely, preg_match() returns false only if there is a pattern compilation error. It returns zero (0) when no matches are made. So this should have rather been:

0 < (int) preg_match( '/background(-image)?\s*:[^;]*?url\(\s*[\'"]?\s*(?<background_image>.+?)\s*[\'"]?\s*\)/', $style, $matches )

Which handles both the error case and the non-match case.

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

If you're merging code through a pull request on GitHub, copy and paste the following into the bottom of the merge commit message.

Co-authored-by: westonruter <[email protected]>
Co-authored-by: thelovekesh <[email protected]>

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

[westonruter]

Released 0.1.1 to WordPress.org.