Don't try to parse strings that don't contain blocks (#3903)

* Short circuit gutenberg_parse_blocks() calls when there are no blocks to parse
* Fix linting errors.
* Add checks for <!--more--> and <!--noteaser-->
* Use gutenberg_content_has_blocks to check for existance of blocks

lib/blocks.php

@@ -53,6 +53,19 @@ function unregister_block_type( $name ) {
  * @return array  Array of parsed block objects.
  */
 function gutenberg_parse_blocks( $content ) {
+	/*
+	 * If there are no blocks in the content, return a single block, rather
+	 * than wasting time trying to parse the string.
+	 */
+	if ( ! gutenberg_content_has_blocks( $content ) ) {
+		return array(
+			array(
+				'attrs'     => array(),
+				'innerHTML' => $content,
+			),
+		);
+	}
+
 	$parser = new Gutenberg_PEG_Parser;
 	return $parser->parse( _gutenberg_utf8_split( $content ) );
 }

phpunit/class-parsing-test.php

@@ -58,7 +58,8 @@ function test_parser_output( $html_filename, $parsed_json_filename ) {
 		$html            = self::strip_r( file_get_contents( $html_path ) );
 		$expected_parsed = json_decode( self::strip_r( file_get_contents( $parsed_json_path ) ), true );
 
-		$result = gutenberg_parse_blocks( $html );
+		$parser = new Gutenberg_PEG_Parser;
+		$result = $parser->parse( _gutenberg_utf8_split( $html ) );
 
 		$this->assertEquals(
 			$expected_parsed,