WP_Theme_JSON::split_selector_list( string $selector ): string[]

Source

protected static function split_selector_list( $selector ): array {
	if ( ! str_contains( $selector, ',' ) ) {
		// See note on trimming CSS whitespace in main loop.
		return array( trim( $selector, " \t\n" ) );
	}

	$selectors         = array();
	$selector_length   = strlen( $selector );
	$parentheses_depth = 0;
	$at                = 0;
	$was_at            = 0;

	while ( $at < $selector_length ) {
		$next_at = $at + strcspn( $selector, '/,\'"()<-\\', $at );
		if ( $next_at >= $selector_length ) {
			break;
		}

		$next_cp = $selector[ $next_at ];

		// Escaped syntax characters do not act as delimiters.
		if ( '\\' === $next_cp ) {
			$at = min( $next_at + 2, $selector_length );
			continue;
		}

		/*
		 * Start of a parenthesized expression, which maintains a stack of parentheses.
		 * For the sake of this function, no selector list will be split inside parentheses.
		 * Therefore it’s possible to jump ahead until this list completes.
		 */
		if ( '(' === $next_cp || ')' === $next_cp ) {
			$parentheses_depth += '(' === $next_cp ? 1 : -1;
			$at                 = $next_at + 1;
			continue;
		}

		// Start of a string, which will be incorporated into the selector in which it’s found.
		if ( "'" === $next_cp || '"' === $next_cp ) {
			$end_of_string = $next_at + 1;
			while ( $end_of_string < $selector_length ) {
				$end_of_string += strcspn( $selector, "{$next_cp}\\", $end_of_string );
				if ( $end_of_string >= $selector_length ) {
					break;
				}

				$end_cp = $selector[ $end_of_string ];

				// Skip escaped characters.
				if ( '\\' === $end_cp ) {
					$end_of_string = $end_of_string + 2;
					continue;
				}

				if ( $next_cp === $end_cp ) {
					++$end_of_string;
					break;
				}

				++$end_of_string;
			}

			$at = $end_of_string;
			continue;
		}

		// Start of a comment, which will be incorporated into the selector in which it’s found.
		if ( '/' === $next_cp && ( $next_at + 1 ) < $selector_length && '*' === $selector[ $next_at + 1 ] ) {
			$comment_end_at = strpos( $selector, '*/', $next_at + 1 );
			$is_terminated  = false !== $comment_end_at;
			$after_comment  = $is_terminated ? $comment_end_at + 2 : strlen( $selector );
			$at             = $after_comment;
			continue;
		}

		// Start of a CDO or CDC, which will be incorporated into the selector in which it’s found.
		if (
			( '<' === $next_cp && 0 === substr_compare( $selector, '<!--', $next_at, 4 ) ) ||
			( '-' === $next_cp && 0 === substr_compare( $selector, '-->', $next_at, 3 ) )
		) {
			$at = $next_at + ( '<' === $next_cp ? 4 : 3 );
			continue;
		}

		// Everything else is either a comma token or part of a selector.
		if ( ',' === $next_cp && 0 === $parentheses_depth ) {
			/**
			 * Trim each selector so that downstream code doesn’t see whitespace
			 * as the first character in a selector and get confused.
			 *
			 * There is inconsistency in this because comments and other syntax
			 * are included which are also not part of the selector itself, but
			 * a tradeoff is made between removing common syntax which carries
			 * no meaning and rarer syntax which leaves auxiliary information.
			 *
			 * > A newline, U+0009 CHARACTER TABULATION, or U+0020 SPACE.
			 * > Note that U+000D CARRIAGE RETURN and U+000C FORM FEED are
			 * > not included in this definition, as they are converted
			 * > to U+000A LINE FEED during preprocessing.
			 *
			 * @see https://www.w3.org/TR/css-syntax/#whitespace
			 * @see https://www.w3.org/TR/css-syntax/#newline
			 */
			$selectors[] = trim( substr( $selector, $was_at, $next_at - $was_at ), " \t\n" );
			$at          = $next_at + 1;
			$was_at      = $at;
			continue;
		}

		$at = $next_at + 1;
	}

	if ( $was_at < $selector_length ) {
		// See note on trimming CSS whitespace in main loop.
		$selectors[] = trim( substr( $selector, $was_at ), " \t\n" );
	}

	return $selectors;
}

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