(perf) avoid duplicate patching in the ts plugin (#1404)

When the tsconfig.json is updated, tsserver would reload the project and it would cause the plugin to be loaded again.

Author: jasonlyu123

packages/typescript-plugin/src/index.ts

@@ -1,5 +1,5 @@
 import { dirname, resolve } from 'path';
-import { decorateLanguageService } from './language-service';
+import { decorateLanguageService, isPatched } from './language-service';
 import { Logger } from './logger';
 import { patchModuleLoader } from './module-loader';
 import { SvelteSnapshotManager } from './svelte-snapshots';
@@ -16,6 +16,11 @@ function init(modules: { typescript: typeof ts }) {
             return info.languageService;
         }
 
+        if (isPatched(info.languageService)) {
+            logger.log('Already patched');
+            return info.languageService;
+        }
+
         configManager.updateConfigFromPluginConfig(info.config);
         if (configManager.getConfig().enable) {
             logger.log('Starting Svelte plugin');

packages/typescript-plugin/src/language-service/index.ts

@@ -10,6 +10,12 @@ import { decorateFindReferences } from './find-references';
 import { decorateGetImplementation } from './implementation';
 import { decorateRename } from './rename';
 
+const sveltePluginPatchSymbol = Symbol('sveltePluginPatchSymbol');
+
+export function isPatched(ls: ts.LanguageService) {
+    return (ls as any)[sveltePluginPatchSymbol] === true;
+}
+
 export function decorateLanguageService(
     ls: ts.LanguageService,
     snapshotManager: SvelteSnapshotManager,
@@ -43,6 +49,11 @@ function createProxyHandler(configManager: ConfigManager): ProxyHandler<ts.Langu
 
     return {
         get(target, p) {
+            // always return patch symbol whether the plugin is enabled or not
+            if (p === sveltePluginPatchSymbol) {
+                return true;
+            }
+
             if (!configManager.getConfig().enable) {
                 return target[p as keyof ts.LanguageService];
             }