Restrict FE assignees to 1

app/assets/javascripts/users_select.js

@@ -388,10 +388,12 @@ import eventHub from './sidebar/event_hub';
               page = $('body').data('page');
               isIssueIndex = page === 'projects:issues:index';
               isMRIndex = (page === page && page === 'projects:merge_requests:index');
-              isSelecting = (user.id !== selectedId);
-              selectedId = isSelecting ? user.id : selectedIdDefault;
               if ($dropdown.hasClass('js-filter-bulk-update') || $dropdown.hasClass('js-issuable-form-dropdown')) {
                 e.preventDefault();
+
+                let isSelecting = (user.id !== selectedId);
+                selectedId = isSelecting ? user.id : selectedIdDefault;
+
                 if (selectedId === gon.current_user_id) {
                   $('.assign-to-me-link').hide();
                 } else {

app/views/projects/boards/components/sidebar/_assignee.html.haml

@@ -16,11 +16,11 @@
         "v-if" => "issue.assignees",
         "v-for" => "assignee in issue.assignees" }
       .dropdown
-        %button.dropdown-menu-toggle.js-user-search.js-author-search.js-multiselect.js-save-user-data.js-issue-board-sidebar{ type: "button", ref: "assigneeDropdown", data: { toggle: "dropdown", field_name: "issue[assignee_ids][]", first_user: (current_user.username if current_user), current_user: "true", project_id: @project.id, null_user: "true", multi_select: "true", dropdown: { header: 'Assignee(s)'} },
+        %button.dropdown-menu-toggle.js-user-search.js-author-search.js-multiselect.js-save-user-data.js-issue-board-sidebar{ type: "button", ref: "assigneeDropdown", data: { toggle: "dropdown", field_name: "issue[assignee_ids][]", first_user: (current_user.username if current_user), current_user: "true", project_id: @project.id, null_user: "true", multi_select: "true", 'max-select' => 1, dropdown: { header: 'Assignee' } },
           ":data-issuable-id" => "issue.id",
           ":data-selected" => "assigneeId",
           ":data-issue-update" => "'#{namespace_project_issues_path(@project.namespace, @project)}/' + issue.id + '.json'" }
-          Select assignee(s)
+          Select assignee
           = icon("chevron-down")
         .dropdown-menu.dropdown-select.dropdown-menu-user.dropdown-menu-selectable.dropdown-menu-author
           = dropdown_title("Assign to")

app/views/shared/issuable/_sidebar.html.haml

@@ -53,17 +53,18 @@
           - issuable.assignees.each do |assignee|
             = hidden_field_tag "#{issuable.to_ability_name}[assignee_ids][]", assignee.id, id: nil
 
-          - options = { toggle_class: 'js-user-search js-author-search', title: 'Assign to', filter: true, dropdown_class: 'dropdown-menu-user dropdown-menu-selectable dropdown-menu-author', placeholder: 'Search users', data: { first_user: (current_user.username if current_user), current_user: true, project_id: (@project.id if @project), author_id: issuable.author_id, field_name: "#{issuable.to_ability_name}[assignee_id]", issue_update: issuable_json_path(issuable), ability_name: issuable.to_ability_name, null_user: true } }
+          - options = { toggle_class: 'js-user-search js-author-search', title: 'Assign to', filter: true, dropdown_class: 'dropdown-menu-user dropdown-menu-selectable dropdown-menu-author', placeholder: 'Search users', data: { first_user: (current_user.username if current_user), current_user: true, project_id: (@project.id if @project), author_id: issuable.author_id, field_name: "#{issuable.to_ability_name}[assignee_ids][]", issue_update: issuable_json_path(issuable), ability_name: issuable.to_ability_name, null_user: true } }
 
           - if issuable.instance_of?(Issue)
             - if issuable.assignees.length == 0
               = hidden_field_tag "#{issuable.to_ability_name}[assignee_ids][]", 0, id: nil
-            - title = 'Select assignee(s)'
+            - title = 'Select assignee'
             - options[:toggle_class] += ' js-multiselect js-save-user-data'
             - options[:data][:field_name] = "#{issuable.to_ability_name}[assignee_ids][]"
             - options[:data][:multi_select] = true
             - options[:data]['dropdown-title'] = title
-            - options[:data]['dropdown-header'] = 'Assignee(s)'
+            - options[:data]['dropdown-header'] = 'Assignee'
+            - options[:data]['max-select'] = 1
           - else
             - title = 'Select assignee'