Themes: Optimize WP_Theme::get_post_templates() for efficiency.

This aims to speed up processing and reduce memory footprint when parsing the `Template Name` and `Template Post Type` headers for themes with many template files by replacing two `file_get_contents()` calls with a single `get_file_data()` call, which only reads the first 8KB of each file instead of the entire contents.

`get_file_data()` already calls `_cleanup_header_comment()` internally, so the parsed output is equivalent to the previous manual cleanup. Additionally, the `extra_theme_headers` filter is now applied, bringing consistency with parsing the other theme file headers, such as in the `WP_Theme` constructor.

Includes unit tests covering the caching behavior, cache invalidation on theme switch, and `get_file_data()` integration.

Follow-up to [20029], [20041], [20317], [20327], [20588], [38951], [62809].

Props gschoppe, MythThrazz, birgire, swissspidy, sukhendu2002, sachinrajcp123, SergeyBiryukov.
Fixes #42513.

git-svn-id: https://develop.svn.wordpress.org/trunk@62810 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov

src/wp-includes/class-wp-theme.php

@@ -1338,13 +1338,22 @@ public function get_post_templates() {
 			$files = (array) $this->get_files( 'php', 1, true );
 
 			foreach ( $files as $file => $full_path ) {
-				if ( ! preg_match( '|Template Name:(.*)$|mi', file_get_contents( $full_path ), $header ) ) {
+				$headers = get_file_data(
+					$full_path,
+					array(
+						'TemplateName'     => 'Template Name',
+						'TemplatePostType' => 'Template Post Type',
+					),
+					'theme'
+				);
+
+				if ( ! $headers['TemplateName'] ) {
 					continue;
 				}
 
 				$types = array( 'page' );
-				if ( preg_match( '|Template Post Type:(.*)$|mi', file_get_contents( $full_path ), $type ) ) {
-					$types = explode( ',', _cleanup_header_comment( $type[1] ) );
+				if ( $headers['TemplatePostType'] ) {
+					$types = explode( ',', $headers['TemplatePostType'] );
 				}
 
 				foreach ( $types as $type ) {
@@ -1353,7 +1362,7 @@ public function get_post_templates() {
 						$post_templates[ $type ] = array();
 					}
 
-					$post_templates[ $type ][ $file ] = _cleanup_header_comment( $header[1] );
+					$post_templates[ $type ][ $file ] = $headers['TemplateName'];
 				}
 			}
 

tests/phpunit/tests/theme/wpThemeGetPostTemplates.php

@@ -47,4 +47,74 @@ public function test_get_post_templates_child_theme() {
 			$post_templates['page']
 		);
 	}
+
+	/**
+	 * @ticket 42513
+	 */
+	public function test_get_post_templates_caches_results() {
+		$theme = wp_get_theme( 'page-templates' );
+		$this->assertNotEmpty( $theme );
+
+		$filter = new MockAction();
+		add_filter( 'extra_theme_headers', array( $filter, 'filter' ) );
+
+		// First call populates the cache.
+		$first_result = $theme->get_post_templates();
+		$this->assertNotEmpty( $first_result );
+		$filter_call_count = $filter->get_call_count();
+		$this->assertGreaterThan( 0, $filter_call_count, 'The `extra_theme_headers` filter should be called at least once.' );
+
+		// Second call should return the same result from cache.
+		$second_result = $theme->get_post_templates();
+		$this->assertSame( $first_result, $second_result );
+		$this->assertSame( $filter_call_count, $filter->get_call_count(), 'The `extra_theme_headers` filter should not have extra calls.' );
+	}
+
+	/**
+	 * @ticket 42513
+	 */
+	public function test_get_post_templates_clears_cache_on_theme_switch() {
+		$theme = wp_get_theme( 'page-templates' );
+		$this->assertNotEmpty( $theme );
+
+		$filter = new MockAction();
+		add_filter( 'extra_theme_headers', array( $filter, 'filter' ) );
+
+		// Populate cache.
+		$theme->get_post_templates();
+
+		$filter_call_count = $filter->get_call_count();
+		$this->assertGreaterThan( 0, $filter_call_count, 'The `extra_theme_headers` filter should be called at least once.' );
+
+		$child_theme = wp_get_theme( 'page-templates-child' );
+		switch_theme( $child_theme['Template'], $child_theme['Stylesheet'] );
+
+		$child_templates = $child_theme->get_post_templates();
+
+		// Child theme should include its own templates.
+		$this->assertArrayHasKey( 'foo', $child_templates );
+		$this->assertArrayHasKey( 'template-top-level-post-types-child.php', $child_templates['foo'] );
+		$this->assertGreaterThan( $filter_call_count, $filter->get_call_count(), 'The `extra_theme_headers` filter should have extra calls.' );
+	}
+
+	/**
+	 * @ticket 42513
+	 */
+	public function test_get_post_templates_uses_get_file_data() {
+		$theme = wp_get_theme( 'page-templates' );
+		$this->assertNotEmpty( $theme );
+
+		$filter = new MockAction();
+		add_filter( 'extra_theme_headers', array( $filter, 'filter' ) );
+
+		$post_templates = $theme->get_post_templates();
+
+		// Verify single-line header format is parsed correctly via get_file_data().
+		$this->assertArrayHasKey( 'page', $post_templates );
+		$this->assertArrayHasKey( 'template-header.php', $post_templates['page'] );
+		$this->assertSame( 'This Template Header Is On One Line', $post_templates['page']['template-header.php'] );
+
+		// Verify the `extra_theme_headers` filter is called.
+		$this->assertGreaterThan( 0, $filter->get_call_count(), 'The `extra_theme_headers` filter should be called at least once.' );
+	}
 }