improve stimulus controller template to import from correct module

Stimulus changed the location of their module from `stimulus` to `@hotwired/stimulus`.
Depending on that, the import in the controller template should change.

For `stimulus` it should be

```js
import { Controller } from "stimulus"
```

For `@hotwired/stimulus` it should be

```js
import { Controller } from "@hotwired/stimulus"
```

Author: lxxxvi

docs/CHANGELOG.md

@@ -7,6 +7,10 @@ title: Changelog
 
 ## main
 
+* Improve Stimulus controller template to import from `stimulus` or `@hotwired/stimulus`.
+
+    *Mario Schüttel*
+
 ## 2.41.0
 
 * Add `sprockets-rails` development dependency to fix test suite failures when using rails@main.

lib/rails/generators/stimulus/component_generator.rb

@@ -12,6 +12,12 @@ def create_stimulus_controller
         template "component_controller.js", destination
       end
 
+      def stimulus_module
+        return "stimulus" if legacy_stimulus?
+
+        "@hotwired/stimulus"
+      end
+
       private
 
       def destination
@@ -21,6 +27,11 @@ def destination
           File.join(component_path, class_path, "#{file_name}_component_controller.js")
         end
       end
+
+      def legacy_stimulus?
+        package_json_pathname = Rails.root.join("package.json")
+        package_json_pathname.exist? && JSON.parse(package_json_pathname.read).dig("dependencies", "stimulus").present?
+      end
     end
   end
 end

lib/rails/generators/stimulus/templates/component_controller.js.tt

@@ -1,4 +1,4 @@
-import { Controller } from "stimulus";
+import { Controller } from "<%= stimulus_module %>";
 
 export default class extends Controller {
   connect() {

test/generators/component_generator_test.rb

@@ -216,10 +216,22 @@ def test_component_with_stimulus_and_inline
     assert_file "app/components/user_component_controller.js"
   end
 
+  def test_component_with_legacy_stimulus_and_sidecar
+    with_package_json({ dependencies: { "stimulus": "0.0.0" } }) do
+      run_generator %w[user --stimulus --sidecar]
+
+      assert_file "app/components/user_component/user_component_controller.js" do |file|
+        assert_match(/import { Controller } from "stimulus"/, file)
+      end
+    end
+  end
+
   def test_component_with_stimulus_and_sidecar
     run_generator %w[user --stimulus --sidecar]
 
-    assert_file "app/components/user_component/user_component_controller.js"
+    assert_file "app/components/user_component/user_component_controller.js" do |file|
+      assert_match(/import { Controller } from "@hotwired\/stimulus"/, file)
+    end
   end
 
   def test_component_with_stimulus_and_sidecar_and_inline
@@ -231,4 +243,14 @@ def test_component_with_stimulus_and_sidecar_and_inline
 
     assert_file "app/components/user_component/user_component_controller.js"
   end
+
+  private
+
+  def with_package_json(content, &block)
+    package_json_pathname = Rails.root.join("package.json")
+    package_json_pathname.write(JSON.generate(content))
+    yield
+  ensure
+    package_json_pathname.delete
+  end
 end