auto-link mentions with user names having symbols

this also handles the case where user_name having '_'

web/react/utils/markdown.jsx

@@ -121,8 +121,11 @@ export class MattermostMarkdownRenderer extends marked.Renderer {
     paragraph(text) {
         let outText = text;
 
+        // required so markdown does not strip '_' from @user_names
+        outText = TextFormatting.doFormatMentions(text);
+
         if (!('emoticons' in this.options) || this.options.emoticon) {
-            outText = TextFormatting.doFormatEmoticons(text);
+            outText = TextFormatting.doFormatEmoticons(outText);
         }
 
         if (this.formattingOptions.singleline) {
@@ -136,7 +139,7 @@ export class MattermostMarkdownRenderer extends marked.Renderer {
         return `<table class="markdown__table"><thead>${header}</thead><tbody>${body}</tbody></table>`;
     }
 
-    text(text) {
-        return TextFormatting.doFormatText(text, this.formattingOptions);
+    text(txt) {
+        return TextFormatting.doFormatText(txt, this.formattingOptions);
     }
 }

web/react/utils/text_formatting.jsx

@@ -47,8 +47,8 @@ export function doFormatText(text, options) {
     const tokens = new Map();
 
     // replace important words and phrases with tokens
-    output = autolinkUrls(output, tokens);
     output = autolinkAtMentions(output, tokens);
+    output = autolinkUrls(output, tokens);
     output = autolinkHashtags(output, tokens);
 
     if (!('emoticons' in options) || options.emoticon) {
@@ -78,6 +78,13 @@ export function doFormatEmoticons(text) {
     return output;
 }
 
+export function doFormatMentions(text) {
+    const tokens = new Map();
+    let output = autolinkAtMentions(text, tokens);
+    output = replaceTokens(output, tokens);
+    return output;
+}
+
 export function sanitizeHtml(text) {
     let output = text;
 
@@ -188,6 +195,7 @@ function autolinkAtMentions(text, tokens) {
 
     let output = text;
     output = output.replace(/(^|\s)(@([a-z0-9.\-_]*))/gi, replaceAtMentionWithToken);
+
     return output;
 }