Merge branches 't/ckeditor5/5988' and 't/ckeditor5/6007' into github-rte

# Conflicts:
#	package.json

.gitignore

@@ -1 +1,4 @@
-node_modules/
+/node_modules/
+/build/
+/package-lock.json
+/yarn.lock

package.json

@@ -10,7 +10,11 @@
     "ckeditor5-plugin"
   ],
   "dependencies": {
-    "@ckeditor/ckeditor5-engine": "^19.0.0"
+    "@ckeditor/ckeditor5-core": "^19.0.0",
+    "@ckeditor/ckeditor5-engine": "^19.0.0",
+    "marked": "^0.7.0",
+    "turndown": "^6.0.0",
+    "turndown-plugin-gfm": "^1.0.2"
   },
   "devDependencies": {
     "eslint": "^5.5.0",

src/gfmdataprocessor.js

@@ -7,11 +7,10 @@
  * @module markdown-gfm/gfmdataprocessor
  */
 
-import marked from './lib/marked/marked';
-import toMarkdown from './lib/to-markdown/to-markdown';
 import HtmlDataProcessor from '@ckeditor/ckeditor5-engine/src/dataprocessor/htmldataprocessor';
-import GFMRenderer from './lib/marked/renderer';
-import converters from './lib/to-markdown/converters';
+
+import markdown2html from './markdown2html/markdown2html';
+import html2markdown, { turndownService } from './html2markdown/html2markdown';
 
 /**
  * This data processor implementation uses GitHub Flavored Markdown as input/output data.
@@ -36,21 +35,26 @@ export default class GFMDataProcessor {
 		this._htmlDP = new HtmlDataProcessor( document );
 	}
 
+	/**
+	 * Keeps the specified element in the output as HTML. This is useful if the editor contains
+	 * features that produce HTML that are not part of the markdon standards.
+	 *
+	 * By default, all HTML tags are removed.
+	 *
+	 * @param element {String} The element name to be kept.
+	 */
+	keepHtml( element ) {
+		turndownService.keep( [ element ] );
+	}
+
 	/**
 	 * Converts the provided Markdown string to view tree.
 	 *
 	 * @param {String} data A Markdown string.
 	 * @returns {module:engine/view/documentfragment~DocumentFragment} The converted view element.
 	 */
 	toView( data ) {
-		const html = marked.parse( data, {
-			gfm: true,
-			breaks: true,
-			tables: true,
-			xhtml: true,
-			renderer: new GFMRenderer()
-		} );
-
+		const html = markdown2html( data );
 		return this._htmlDP.toView( html );
 	}
 
@@ -63,7 +67,6 @@ export default class GFMDataProcessor {
 	 */
 	toData( viewFragment ) {
 		const html = this._htmlDP.toData( viewFragment );
-
-		return toMarkdown( html, { gfm: true, converters } );
+		return html2markdown( html );
 	}
 }

src/html2markdown/html2markdown.js

@@ -0,0 +1,82 @@
+/**
+ * @license Copyright (c) 2003-2019, CKSource - Frederico Knabben. All rights reserved.
+ * For licensing, see LICENSE.md.
+ */
+
+import TurndownService from 'turndown';
+import { gfm } from 'turndown-plugin-gfm';
+
+// Overrides the escape() method, enlarging it.
+{
+	const originalEscape = TurndownService.prototype.escape;
+	TurndownService.prototype.escape = function( string ) {
+		// Urls should not be escaped. Our strategy is using a regex to find them and escape everything
+		// which is out of the matches parts.
+
+		// eslint-disable-next-line max-len
+		const regex = /\b(?:https?:\/\/|www\.)(?:[^\s()<>]+|\(([^\s()<>]+|(\([^\s()<>]+\)))*\))+(?:\(([^\s()<>]+|(\([^\s()<>]+\)))*\)|[^\s`!()[\]{};:'".,<>?«»“”‘’])/g;
+
+		let escaped = '';
+		let lastIndex = 0;
+		let m;
+		do {
+			m = regex.exec( string );
+
+			// The substring should to to the matched index or, if nothing found, the end of the string.
+			const index = m ? m.index : string.length;
+
+			// Append the substring between the last match and the current one (if anything).
+			if ( index > lastIndex ) {
+				escaped += escape( string.substring( lastIndex, index ) );
+			}
+
+			// Append the match itself now, if anything.
+			m && ( escaped += m[ 0 ] );
+
+			lastIndex = regex.lastIndex;
+		}
+		while ( m );
+
+		return escaped;
+
+		function escape( string ) {
+			string = originalEscape( string );
+
+			// Escape "<".
+			string = string.replace( /</g, '\\<' );
+
+			return string;
+		}
+	};
+}
+
+const turndownService = new TurndownService( {
+	codeBlockStyle: 'fenced',
+	hr: '---',
+	headingStyle: 'atx'
+} );
+
+turndownService.use( [
+	gfm,
+	todoList
+] );
+
+export default function html2markdown( html ) {
+	return turndownService.turndown( html );
+}
+
+export { turndownService };
+
+// This is a copy of the original taskListItems rule from turdown-plugin-gfm, with minor changes.
+function todoList( turndownService ) {
+	turndownService.addRule( 'taskListItems', {
+		filter( node ) {
+			return node.type === 'checkbox' &&
+				// Changes here as CKEditor outputs a deeper structure.
+				( node.parentNode.nodeName === 'LI' || node.parentNode.parentNode.nodeName === 'LI' );
+		},
+		replacement( content, node ) {
+			return ( node.checked ? '[x]' : '[ ]' ) + ' ';
+		}
+	} );
+}