markdown: Disable definition/reference links in marked.

We had disabled reference style links in bugdown, however,
we hadn't disabled them in marked. This commit rectifies
that and adds test cases for the same.

Fixes #11350.

static/third/marked/lib/marked.js

@@ -356,14 +356,7 @@ Lexer.prototype.token = function(src, top, bq) {
     }
 
     // def
-    if ((!bq && top) && (cap = this.rules.def.exec(src))) {
+    // We disable definition style links in Zulip.
-      src = src.substring(cap[0].length);
-      this.tokens.links[cap[1].toLowerCase()] = {
-        href: cap[2],
-        title: cap[3]
-      };
-      continue;
-    }
 
     // table (gfm)
     if (top && (cap = this.rules.table.exec(src))) {

zerver/tests/fixtures/markdown_test_cases.json

@@ -120,6 +120,16 @@
       "marked_expected_output": "<p>  notcode</p>",
       "text_content": "notcode"
     },
+    {
+      "name": "reference_links_disabled",
+      "input": "Hello [world]\n\n[world]: https://google.com",
+      "expected_output": "<p>Hello [world]</p>\n<p>[world]: <a href=\"https://google.com\" target=\"_blank\" title=\"https://google.com\">https://google.com</a></p>"
+    },
+    {
+      "name": "reference_links_disabled_2",
+      "input": "Hello [world][ref-name]\n\n[ref-name]: https://google.com",
+      "expected_output": "<p>Hello [world][ref-name]</p>\n<p>[ref-name]: <a href=\"https://google.com\" target=\"_blank\" title=\"https://google.com\">https://google.com</a></p>"
+    },
     {
       "name": "ulist_standard",
       "input": "Some text with a list:\n\n* One item\n* Two items\n* Three items",