Merge pull request #367 from haskellfoundation/404

Higher-tech 404 page

Author: david-christiansen

message-index/404.html

@@ -5,8 +5,9 @@
 <div id="documentation-pointer">Page not found.</div>
 
 <script>
-const messageRe = /^\/messages\/[A-Z]+-[0-9]+/;
+const messageRe = /^\/messages\/([A-Z]+-[0-9]+)/;
 if (messageRe.test(window.location.pathname)) {
-  document.getElementById("documentation-pointer").innerHTML = "This message is currently undocumented. You can help out by <a href=\"https://github.com/haskellfoundation/error-message-index/issues\">opening an issue</a> or <a href=\"https://github.com/haskellfoundation/error-message-index/pulls\">contributing documentation</a>."
+  const messageNum = window.location.pathname.match(messageRe)[1];
+  document.getElementById("documentation-pointer").innerHTML = "Message <code>" + messageNum + "</code> is currently undocumented. You can help out by <a href=\"https://github.com/haskellfoundation/error-message-index/issues?q=is%3Aissue+is%3Aopen+" + messageNum + "\">opening or commenting on an issue</a> or <a href=\"https://github.com/haskellfoundation/error-message-index/blob/main/CONTRIBUTING.md\">contributing documentation</a>."
 }
 </script>