FIX: supports user/group mentions and category hashtags when quoting posts

app/assets/javascripts/discourse/lib/to-markdown.js.es6

@@ -126,6 +126,14 @@ class Tag {
       decorate(text) {
         const attr = this.element.attributes;
 
+        if (/^mention/.test(attr.class) && "@" === text[0]) {
+          return text;
+        }
+
+        if ("hashtag" === attr.class && "#" === text[0]) {
+          return text;
+        }
+
         if (attr.href && text !== attr.href) {
           text = text.replace(/\n{2,}/g, "\n");
           return "[" + text + "](" + attr.href + ")";

test/javascripts/lib/to-markdown-test.js.es6

@@ -104,7 +104,7 @@ QUnit.test("converts table tags", assert => {
       <tbody>
         <tr><td>Lorem</td><td>ipsum</td></tr>
         <tr><td><b>dolor</b></td> <td><i>sit amet</i></td> </tr>
-        
+
         </tbody>
 </table>
   `;
@@ -286,3 +286,16 @@ QUnit.test("converts list tag from word", assert => {
   const markdown = `Sample\n\n* **Item 1**\n  * *Item 2*\n    * Item 3\n* Item 4\n\nList`;
   assert.equal(toMarkdown(html), markdown);
 });
+
+QUnit.test("keeps mention/hash class", assert => {
+  const html = `
+    <p>User mention: <a class="mention" href="/u/discourse">@discourse</a></p>
+    <p>Group mention: <a class="mention-group" href="/groups/discourse">@discourse-group</a></p>
+    <p>Category link: <a class="hashtag" href="/c/foo/1">#<span>foo</span></a></p>
+    <p>Sub-category link: <a class="hashtag" href="/c/foo/bar/2">#<span>foo:bar</span></a></p>
+  `;
+
+  const markdown = `User mention: @discourse\n\nGroup mention: @discourse-group\n\nCategory link: #foo\n\nSub-category link: #foo:bar`;
+
+  assert.equal(toMarkdown(html), markdown);
+});