Plugins: Skips existence of module.js for renderer plugins (#19318)

* Fix: Skips test for module.js for plugins of renderer type
Fixes #19130

* Refactor: Changes after PR comments

* Chore: Fixes go lint issue

pkg/plugins/plugins.go

@@ -217,7 +217,7 @@ func (scanner *PluginScanner) loadPluginJson(pluginJsonFilePath string) error {
 	loader = reflect.New(reflect.TypeOf(pluginGoType)).Interface().(PluginLoader)
 
 	// External plugins need a module.js file for SystemJS to load
-	if !strings.HasPrefix(pluginJsonFilePath, setting.StaticRootPath) {
+	if !strings.HasPrefix(pluginJsonFilePath, setting.StaticRootPath) && !scanner.IsBackendOnlyPlugin(pluginCommon.Type) {
 		module := filepath.Join(filepath.Dir(pluginJsonFilePath), "module.js")
 		if _, err := os.Stat(module); os.IsNotExist(err) {
 			plog.Warn("Plugin missing module.js",
@@ -231,6 +231,10 @@ func (scanner *PluginScanner) loadPluginJson(pluginJsonFilePath string) error {
 	return loader.Load(jsonParser, currentDir)
 }
 
+func (scanner *PluginScanner) IsBackendOnlyPlugin(pluginType string) bool {
+	return pluginType == "renderer"
+}
+
 func GetPluginMarkdown(pluginId string, name string) ([]byte, error) {
 	plug, exists := Plugins[pluginId]
 	if !exists {

pkg/plugins/plugins_test.go

@@ -42,4 +42,18 @@ func TestPluginScans(t *testing.T) {
 		So(Apps["test-app"].Info.Screenshots[1].Path, ShouldEqual, "public/plugins/test-app/img/screenshot2.png")
 	})
 
+	Convey("When checking if renderer is backend only plugin", t, func() {
+		pluginScanner := &PluginScanner{}
+		result := pluginScanner.IsBackendOnlyPlugin("renderer")
+
+		So(result, ShouldEqual, true)
+	})
+
+	Convey("When checking if app is backend only plugin", t, func() {
+		pluginScanner := &PluginScanner{}
+		result := pluginScanner.IsBackendOnlyPlugin("app")
+
+		So(result, ShouldEqual, false)
+	})
+
 }