Fix escaping markdown by rendering plaintext

We still need to parse "plaintext" messages through the markdown
renderer so that escappes are rendered properly.

Fixes vector-im/riot-web#2870.

Signed-off-by: Johannes Löthberg <johannes@kyriasis.com>

src/Markdown.js

@@ -56,11 +56,12 @@ export default class Markdown {
         return is_plain;
     }
 
-    toHTML() {
+    render(html) {
         const parser = new commonmark.Parser();
 
         const renderer = new commonmark.HtmlRenderer({safe: true});
         const real_paragraph = renderer.paragraph;
+        if (html) {
             renderer.paragraph = function(node, entering) {
                 // If there is only one top level node, just return the
                 // bare text: it's a single line of text and so should be
@@ -75,6 +76,13 @@ export default class Markdown {
                     real_paragraph.call(this, node, entering);
                 }
             }
+        } else {
+            renderer.paragraph = function(node, entering) {
+                if (entering) {
+                    this.lit('\n\n');
+                }
+            }
+        }
 
         var parsed = parser.parse(this.input);
         return renderer.render(parsed);

src/components/views/rooms/MessageComposerInput.js

@@ -401,7 +401,7 @@ export default class MessageComposerInput extends React.Component {
         let contentState = null;
         if (enabled) {
             const md = new Markdown(this.state.editorState.getCurrentContent().getPlainText());
-            contentState = RichText.HTMLtoContentState(md.toHTML());
+            contentState = RichText.HTMLtoContentState(md.render(true));
         } else {
             let markdown = stateToMarkdown(this.state.editorState.getCurrentContent());
             if (markdown[markdown.length - 1] === '\n') {
@@ -523,8 +523,10 @@ export default class MessageComposerInput extends React.Component {
             );
         } else {
             const md = new Markdown(contentText);
-            if (!md.isPlainText()) {
-                contentHTML = md.toHTML();
+            if (md.isPlainText()) {
+                contentText = md.render(false);
+            } else {
+                contentHTML = md.render(true);
             }
         }