Source

File: wp-includes/class-wp-theme.php

private static function scandir( $path, $extensions = null, $depth = 0, $relative_path = '' ) {
		if ( ! is_dir( $path ) ) {
			return false;
		}

		if ( $extensions ) {
			$extensions  = (array) $extensions;
			$_extensions = implode( '|', $extensions );
		}

		$relative_path = trailingslashit( $relative_path );
		if ( '/' === $relative_path ) {
			$relative_path = '';
		}

		$results = scandir( $path );
		$files   = array();

		/**
		 * Filters the array of excluded directories and files while scanning theme folder.
		 *
		 * @since 4.7.4
		 *
		 * @param string[] $exclusions Array of excluded directories and files.
		 */
		$exclusions = (array) apply_filters( 'theme_scandir_exclusions', array( 'CVS', 'node_modules', 'vendor', 'bower_components' ) );

		foreach ( $results as $result ) {
			if ( '.' === $result[0] || in_array( $result, $exclusions, true ) ) {
				continue;
			}
			if ( is_dir( $path . '/' . $result ) ) {
				if ( ! $depth ) {
					continue;
				}
				$found = self::scandir( $path . '/' . $result, $extensions, $depth - 1, $relative_path . $result );
				$files = array_merge_recursive( $files, $found );
			} elseif ( ! $extensions || preg_match( '~\.(' . $_extensions . ')$~', $result ) ) {
				$files[ $relative_path . $result ] = $path . '/' . $result;
			}
		}

		return $files;
	}