Plugins: Selectively load plugins using script tags (#85750)

* feat(plugins): introduce logic to selectively load fe plugins via script tags

* feat(plugins): extend cache to store isAngular flag. use isAngular in shouldFetch

* revert(plugins): remove unused prepareImport from SystemJSWithLoaderHooks type

* fix(plugins): cache[path] maybe undefined if not registered or invalidated

* Update public/app/features/plugins/plugin_loader.ts

Co-authored-by: Levente Balogh <balogh.levente.hu@gmail.com>

---------

Co-authored-by: Levente Balogh <balogh.levente.hu@gmail.com>

public/app/features/plugins/loader/cache.ts

@@ -1,17 +1,22 @@
 import { clearPluginSettingsCache } from '../pluginSettings';
 
-const cache: Record<string, string> = {};
+const cache: Record<string, CacheablePlugin> = {};
 const initializedAt: number = Date.now();
 
 type CacheablePlugin = {
   path: string;
   version: string;
+  isAngular?: boolean;
 };
 
-export function registerPluginInCache({ path, version }: CacheablePlugin): void {
+export function registerPluginInCache({ path, version, isAngular }: CacheablePlugin): void {
   const key = extractPath(path);
   if (key && !cache[key]) {
-    cache[key] = encodeURI(version);
+    cache[key] = {
+      version: encodeURI(version),
+      isAngular,
+      path,
+    };
   }
 }
 
@@ -28,12 +33,19 @@ export function resolveWithCache(url: string, defaultBust = initializedAt): stri
   if (!path) {
     return `${url}?_cache=${defaultBust}`;
   }
-
+  const version = cache[path]?.version;
-  const version = cache[path];
   const bust = version || defaultBust;
   return `${url}?_cache=${bust}`;
 }
 
+export function getPluginFromCache(path: string): CacheablePlugin | undefined {
+  const key = extractPath(path);
+  if (!key) {
+    return;
+  }
+  return cache[key];
+}
+
 function extractPath(address: string): string | undefined {
   const match = /\/?.+\/(plugins\/.+\/module)\.js/i.exec(address);
   if (!match) {

public/app/features/plugins/loader/types.ts

@@ -1,7 +1,7 @@
 // Extend the System type with the loader hooks we use
 // to provide backwards compatibility with older version of Systemjs
 export type SystemJSWithLoaderHooks = typeof System & {
-  shouldFetch: () => Boolean;
+  shouldFetch: (url: string) => Boolean;
   fetch: (url: string, options?: Record<string, unknown>) => Promise<Response>;
   onload: (err: unknown, id: string) => void;
 };

public/app/features/plugins/plugin_loader.ts

@@ -11,14 +11,14 @@ import { DataQuery } from '@grafana/schema';
 import { GenericDataSourcePlugin } from '../datasources/types';
 
 import builtInPlugins from './built_in_plugins';
-import { registerPluginInCache } from './loader/cache';
+import { getPluginFromCache, registerPluginInCache } from './loader/cache';
 // SystemJS has to be imported before the sharedDependenciesMap
 import { SystemJS } from './loader/systemjs';
 // eslint-disable-next-line import/order
 import { sharedDependenciesMap } from './loader/sharedDependencies';
 import { decorateSystemJSFetch, decorateSystemJSResolve, decorateSystemJsOnload } from './loader/systemjsHooks';
 import { SystemJSWithLoaderHooks } from './loader/types';
-import { buildImportMap, resolveModulePath } from './loader/utils';
+import { buildImportMap, isHostedOnCDN, resolveModulePath } from './loader/utils';
 import { importPluginModuleInSandbox } from './sandbox/sandbox_plugin_loader';
 import { isFrontendSandboxSupported } from './sandbox/utils';
 
@@ -28,9 +28,13 @@ SystemJS.addImportMap({ imports });
 
 const systemJSPrototype: SystemJSWithLoaderHooks = SystemJS.constructor.prototype;
 
-// Monaco Editors reliance on RequireJS means we need to transform
+// This instructs SystemJS to load a plugin using fetch and eval if it returns a truthy value, otherwise it will load the plugin using a script tag.
-// the content of the plugin code at runtime which can only be done with fetch/eval.
+// We only want to fetch and eval plugins that are hosted on a CDN or are Angular plugins.
-systemJSPrototype.shouldFetch = () => true;
+systemJSPrototype.shouldFetch = function (url) {
+  const pluginInfo = getPluginFromCache(url);
+
+  return isHostedOnCDN(url) || Boolean(pluginInfo?.isAngular);
+};
 
 const originalImport = systemJSPrototype.import;
 // Hook Systemjs import to support plugins that only have a default export.
@@ -68,7 +72,7 @@ export async function importPluginModule({
   isAngular?: boolean;
 }): Promise<System.Module> {
   if (version) {
-    registerPluginInCache({ path, version });
+    registerPluginInCache({ path, version, isAngular });
   }
 
   const builtIn = builtInPlugins[path];