Themes: Improve the performance of _get_block_templates_paths.

This avoids redundant recursive lookups for block template paths in the same base directory by implementing a static cache. It also replaces an potentially expensive `file_exists` call in favor of doing recursive iteration of files inside a try/catch block. 

Props thekt12, spacedmonkey, flixos90, mukesh27, joemcgill.
Fixes #58196.


git-svn-id: https://develop.svn.wordpress.org/trunk@57215 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/block-template-utils.php

@@ -224,14 +224,21 @@ static function ( $item ) {
  * @return string[] A list of paths to all template part files.
  */
 function _get_block_templates_paths( $base_directory ) {
+	static $template_path_list = array();
+	if ( isset( $template_path_list[ $base_directory ] ) ) {
+		return $template_path_list[ $base_directory ];
+	}
 	$path_list = array();
-	if ( file_exists( $base_directory ) ) {
+	try {
 		$nested_files      = new RecursiveIteratorIterator( new RecursiveDirectoryIterator( $base_directory ) );
 		$nested_html_files = new RegexIterator( $nested_files, '/^.+\.html$/i', RecursiveRegexIterator::GET_MATCH );
 		foreach ( $nested_html_files as $path => $file ) {
 			$path_list[] = $path;
 		}
+	} catch ( Exception $e ) {
+		// Do nothing.
 	}
+	$template_path_list[ $base_directory ] = $path_list;
 	return $path_list;
 }
 

tests/phpunit/tests/block-template.php

@@ -387,6 +387,49 @@ public function data_get_block_theme_folders() {
 		);
 	}
 
+	/**
+	 * Tests `_get_block_templates_paths()` for an invalid directory.
+	 *
+	 * @ticket 58196
+	 *
+	 * @covers ::_get_block_templates_paths
+	 */
+	public function test_get_block_templates_paths_dir_exists() {
+		$theme_dir = get_template_directory();
+		// Templates in the current theme.
+		$templates = array(
+			'parts/small-header.html',
+			'templates/custom-single-post-template.html',
+			'templates/index.html',
+			'templates/page-home.html',
+			'templates/page.html',
+			'templates/single.html',
+		);
+
+		$expected_template_paths = array_map(
+			static function ( $template ) use ( $theme_dir ) {
+				return $theme_dir . '/' . $template;
+			},
+			$templates
+		);
+
+		$template_paths = _get_block_templates_paths( $theme_dir );
+		$this->assertSameSets( $expected_template_paths, $template_paths );
+	}
+
+	/**
+	 * Test _get_block_templates_paths() for a invalid dir.
+	 *
+	 * @ticket 58196
+	 *
+	 * @covers ::_get_block_templates_paths
+	 */
+	public function test_get_block_templates_paths_dir_doesnt_exists() {
+		// Should return empty array for invalid path.
+		$template_paths = _get_block_templates_paths( '/tmp/random-invalid-theme-path' );
+		$this->assertSame( array(), $template_paths );
+	}
+
 	/**
 	 * Registers a test block to log `in_the_loop()` results.
 	 *