Unnecessarily check to see site is using a child theme in the theme functions.

[spacedmonkey]

Follow on from #58576 / [56357].

There are a number of functions methods that check to see if file exists in a child theme before falling back to parent theme. However these functions do not check to see if current theme. These functions include.

• ​WP_Theme::get_file_path
• ​get_theme_file_path
• ​get_theme_file_uri

The function is_child_theme can not be used, as TEMPLATEPATH and STYLESHEETPATH, might be different from the result of get_stylesheet_directory() and get_template_directory(). These functions have filters.

Only check to see if file exists if the current theme is a child theme. is_child_theme can not be used as get_stylesheet_directory has a filter.

Trac ticket: https://core.trac.wordpress.org/ticket/59279#ticket

[spacedmonkey]

We could maybe include _get_block_template_file in this.

[spacedmonkey]

Brenchmark data.

PHP 7.4.33, WordPress develop docker env. Trunk - [56512].

Theme - 2021

	Trunk	PR
Response Time (median)	54.37	54.08
wp-load-alloptions-query (median)	0.56	0.55
wp-before-template (median)	20.24	20.1
wp-template (median)	29.57	29.29
wp-total (median)	49.86	49.56

Theme 2022

	Trunk	PR
Response Time (median)	131.74	128.89
wp-load-alloptions-query (median)	0.59	0.58
wp-before-template (median)	82.09	79.87
wp-template (median)	44.99	44.79
wp-total (median)	127.35	124.57

Blackfire see a 6% improvement ( on 2022 theme )
​https://blackfire.io/profiles/compare/3caa6f25-0dea-4cd7-a545-4fef945deb0f/graph

Trac ticket: https://core.trac.wordpress.org/ticket/59279

Committed https://core.trac.wordpress.org/changeset/56522

[spacedmonkey]

In 56523:

Themes: Remove unnecessary check if file exists in the theme functions.

Previously, several functions and methods in themes api were designed to check for the existence of files in a child theme before falling back to the parent theme. However, these checks did not consider whether the current theme was a child theme or not, resulting in unnecessary file existence checks for non-child themes. Check to see if stylesheet directory matches the template directory before doing the file exists. This optimization helps reduce unnecessary file system access, as file existence checks can be resource-intensive in PHP.

The following functions and methods have been updated as part of this enhancement:

• WP_Theme::get_file_path
• get_theme_file_path
• get_theme_file_uri

Props spacedmonkey, flixos90, sabernhardt, 10upsimon, mukesh27.
Fixes #59279.

Committed ​https://github.com/WordPress/wordpress-develop/commit/bd594f72a83e0512d60aec5436ab653ed5966678