Fixes #3636 - Replacing a mention with a new leads to mentioning both agents.

app/assets/javascripts/app/lib/base/jquery.textmodule.js

@@ -43,6 +43,7 @@
 
   Plugin.prototype.bindEvents = function () {
     this.$element.on('keydown', this.onKeydown.bind(this))
+    this.$element.on('keyup', this.onKeyup.bind(this))
     // using onInput event to trigger onKeyPress behavior
     // since keyPress doesn't work on Mobile Chrome / Android
     this.$element.on('input', this.onKeypress.bind(this))
@@ -150,6 +151,15 @@
     }
   }
 
+  Plugin.prototype.onKeyup = function (e) {
+
+    // in normal use we make sure that mentions
+    // which has no text anymore get deleted
+    if (e.keyCode == 8 && !this.buffer) {
+      this.removeInvalidMentions()
+    }
+  }
+
   Plugin.prototype.onKeypress = function (e) {
     this.log('BUFF', this.buffer, e.keyCode, String.fromCharCode(e.which))
 
@@ -203,6 +213,15 @@
     }
   }
 
+  // remove invalid mentions
+  Plugin.prototype.removeInvalidMentions = function() {
+    this.$element.find('a[data-mention-user-id]').each(function() {
+      if ($(this).text() != '') return true
+
+      $(this).remove()
+    })
+  }
+
   // check if at least one trigger is available with the given prefix
   Plugin.prototype.hasAvailableTriggers = function(prefix) {
     var result = _.find(this.helpers, function(helper) {

spec/system/examples/text_modules_examples.rb

@@ -1,7 +1,7 @@
 # Copyright (C) 2012-2021 Zammad Foundation, http://zammad-foundation.org/
 
 RSpec.shared_examples 'text modules' do |path:|
-
+  let!(:agent_fixed_name)          { create :agent, firstname: 'FFFF1', lastname: 'GGGG1', groups: [Group.find_by(name: 'Users')] }
   let!(:group1)                    { create :group }
   let!(:group2)                    { create :group }
   let!(:text_module_without_group) { create :text_module }
@@ -40,6 +40,34 @@ RSpec.shared_examples 'text modules' do |path:|
     end
   end
 
+  it 'does delete empty mentions (issue #3636 / FF only)' do
+    visit path
+    within(:active_content) do
+      find('select[name="group_id"]').select('Users')
+      find(:richtext).send_keys('@@FFFF1')
+      find(:richtext).send_keys(:enter)
+      find(:richtext).send_keys(:enter)
+      (agent_fixed_name.firstname.length + agent_fixed_name.lastname.length + 2).times do
+        find(:richtext).send_keys(:backspace)
+      end
+      expect(find(:richtext).all('a[data-mention-user-id]', visible: :all).count).to eq(0)
+    end
+  end
+
+  it 'does delete empty mentions (issue #3636 / simulation)' do
+    visit path
+    within(:active_content) do
+      find('select[name="group_id"]').select('Users')
+      find(:richtext).send_keys('@@FFFF1')
+      find(:richtext).send_keys(:enter)
+      find(:richtext).send_keys(:enter)
+      find(:richtext).send_keys('test')
+      page.execute_script("$('a[data-mention-user-id]').first().html('<br>')")
+      find(:richtext).send_keys(:backspace)
+      expect(find(:richtext).all('a[data-mention-user-id]', visible: :all).count).to eq(0)
+    end
+  end
+
   it 'supports group-dependent text modules' do
 
     # give user access to all groups including those created