(perf) improve svelte-check performance (#872)

Because of the setTimeout in the debounceSameArg. The document update in LSAndTSDocResolver is actually done after all the diagnostic is done. Because of that, the typescript language service has to rebuild its type checker multiple times due to a new document being loaded in. Fix that by not debouncing the call on a new document. This makes svelte-check run a lot faster.

Author: jasonlyu123

packages/language-server/src/plugins/typescript/LSAndTSDocResolver.ts

@@ -19,17 +19,24 @@ export class LSAndTSDocResolver {
         private readonly configManager: LSConfigManager,
         private readonly transformOnTemplateError = true
     ) {
+        const handleDocumentChange = (document: Document) => {
+            // This refreshes the document in the ts language service
+            this.getLSAndTSDoc(document);
+        };
         docManager.on(
             'documentChange',
             debounceSameArg(
-                async (document: Document) => {
-                    // This refreshes the document in the ts language service
-                    this.getLSAndTSDoc(document);
-                },
+                handleDocumentChange,
                 (newDoc, prevDoc) => newDoc.uri === prevDoc?.uri,
                 1000
             )
         );
+
+        // New files would cause typescript to rebuild its type-checker.
+        // Open it immediately to reduce rebuilds in the startup
+        // where multiple files and their dependencies
+        // being loaded in a short period of times
+        docManager.on('documentOpen', handleDocumentChange);
     }
 
     /**