Add frontend support for parsing assignee_username[] parameters

app/assets/javascripts/filtered_search/filtered_search_token_keys_issues_ee.js

@@ -18,6 +18,13 @@ const weightConditions = [{
   value: 'any',
 }];
 
+const alternativeTokenKeys = [{
+  key: 'assignee',
+  type: 'string',
+  param: 'username',
+  symbol: '@',
+}];
+
 class FilteredSearchTokenKeysIssuesEE extends gl.FilteredSearchTokenKeys {
   static init(availableFeatures) {
     this.availableFeatures = availableFeatures;
@@ -30,6 +37,7 @@ class FilteredSearchTokenKeysIssuesEE extends gl.FilteredSearchTokenKeys {
     if (this.availableFeatures && this.availableFeatures.multipleAssignees) {
       const assigneeTokenKey = tokenKeys.find(tk => tk.key === 'assignee');
       assigneeTokenKey.type = 'array';
+      assigneeTokenKey.param = 'username[]';
     }
 
     tokenKeys.push(weightTokenKey);
@@ -42,7 +50,7 @@ class FilteredSearchTokenKeysIssuesEE extends gl.FilteredSearchTokenKeys {
   }
 
   static getAlternatives() {
-    return super.getAlternatives();
+    return alternativeTokenKeys.concat(super.getAlternatives());
   }
 
   static getConditions() {
@@ -62,8 +70,8 @@ class FilteredSearchTokenKeysIssuesEE extends gl.FilteredSearchTokenKeys {
 
   static searchByKeyParam(keyParam) {
     const tokenKeys = FilteredSearchTokenKeysIssuesEE.get();
-    const alternativeTokenKeys = FilteredSearchTokenKeysIssuesEE.getAlternatives();
-    const tokenKeysWithAlternative = tokenKeys.concat(alternativeTokenKeys);
+    const alternatives = FilteredSearchTokenKeysIssuesEE.getAlternatives();
+    const tokenKeysWithAlternative = tokenKeys.concat(alternatives);
 
     return tokenKeysWithAlternative.find((tokenKey) => {
       let tokenKeyParam = tokenKey.key;