Introduces Stimulus as a Javascript framework (#42510):

* old @application.js@ from @app/assets/javascripts@ become @application-legacy.js@ in favour of @application.js@ provided by Stimulus
 * adds @importmap@ gem to handle JavaScript modules using logical names that map to versioned/digested files
 
 Stimulus will be used for new functionality and, over time, to migrate existing features from JQuery / JQuery UI.

git-svn-id: https://svn.redmine.org/redmine/trunk@23697 e93f8b46-1217-0410-a6f0-8f06a7374b81

Gemfile

@@ -16,6 +16,8 @@ gem 'addressable'
 gem 'rubyzip', '~> 2.4.0'
 gem 'propshaft', '~> 1.1.0'
 gem 'rack', '>= 3.1.3'
+gem "stimulus-rails", "~> 1.3"
+gem "importmap-rails", "~> 2.0"
 
 #  Ruby Standard Gems
 gem 'csv', '~> 3.3.2'

app/helpers/application_helper.rb

@@ -1805,7 +1805,7 @@ module ApplicationHelper
     if Setting.wiki_tablesort_enabled?
       tags << javascript_include_tag('tablesort-5.2.1.min.js', 'tablesort-5.2.1.number.min.js')
     end
-    tags << javascript_include_tag('application', 'responsive')
+    tags << javascript_include_tag('application-legacy', 'responsive')
     unless User.current.pref.warn_on_leaving_unsaved == '0'
       warn_text = escape_javascript(l(:text_warn_on_leaving_unsaved))
       tags <<

app/javascript/application.js

@@ -0,0 +1 @@
+import "controllers"

app/javascript/controllers/application.js

@@ -0,0 +1,8 @@
+import { Application } from '@hotwired/stimulus'
+
+const application = Application.start()
+
+application.debug = false
+window.Stimulus   = application
+
+export { application }

app/javascript/controllers/index.js

@@ -0,0 +1,3 @@
+import { application } from "controllers/application"
+import { eagerLoadControllersFrom } from "@hotwired/stimulus-loading"
+eagerLoadControllersFrom("controllers", application)

app/views/layouts/base.html.erb

@@ -10,6 +10,7 @@
 <%= favicon %>
 <%= stylesheet_link_tag 'jquery/jquery-ui-1.13.2', 'tribute-5.1.3', 'application', 'responsive', :media => 'all' %>
 <%= stylesheet_link_tag 'rtl', :media => 'all' if l(:direction) == 'rtl' %>
+<%= javascript_importmap_tags %>
 <%= javascript_heads %>
 <%= heads_for_theme %>
 <%= heads_for_i18n %>

bin/importmap

@@ -0,0 +1,4 @@
+#!/usr/bin/env ruby
+
+require_relative "../config/application"
+require "importmap/commands"

config/importmap.rb

@@ -0,0 +1,6 @@
+# Pin npm packages by running ./bin/importmap
+
+pin "application"
+pin "@hotwired/stimulus", to: "stimulus.min.js"
+pin "@hotwired/stimulus-loading", to: "stimulus-loading.js"
+pin_all_from "app/javascript/controllers", under: "controllers"