perf: cache exp result for not-started experiment (#711)

Signed-off-by: Yan Zhang <[email protected]>

Author: Eskibear

src/utils/walkthrough.ts

@@ -5,11 +5,15 @@ import { workspace } from "vscode";
 import { getExpService } from "../exp";
 import { TreatmentVariables } from "../exp/TreatmentVariables";
 
-export function isWalkthroughEnabled() {
-
-    const fromExp = getExpService()?.getTreatmentVariableAsync<boolean>(TreatmentVariables.VSCodeConfig, TreatmentVariables.JavaWalkthroughEnabled, true /* checkCache */) ?? false;
-    // 	can be overridden by local settings "experiments.override.gettingStarted.overrideCategory.vscjava.vscode-java-pack#javaWelcome.when": "true"
-    const fromSettings = workspace.getConfiguration("experiments.override.gettingStarted.overrideCategory").get<string>("vscjava.vscode-java-pack#javaWelcome.when") === "true";
+// local cache before EXP starts, otherwise it always returns undefined, and keeps querying service.
+let fromExpCache: boolean;
+export async function isWalkthroughEnabled() {
+    const fromExp = fromExpCache ?? await getExpService()?.getTreatmentVariableAsync<boolean>(TreatmentVariables.VSCodeConfig, TreatmentVariables.JavaWalkthroughEnabled, true /* checkCache */) ?? false;
+    fromExpCache = fromExp;
+    
+    // can be overridden by local settings "experiments.override.gettingStarted.overrideCategory.vscjava.vscode-java-pack.javaWelcome.when": "true"
+    // '#' -> '.' since https://github.com/microsoft/vscode/commit/fe671f300845ca5161885125b1e12d43fc25ccf8
+    const fromSettings = workspace.getConfiguration("experiments.override.gettingStarted.overrideCategory").get<string>("vscjava.vscode-java-pack.javaWelcome.when") === "true";
 
     return fromExp || fromSettings;
-}
+}

src/welcome/index.ts

@@ -86,8 +86,8 @@ const setFirstTimeRun = (context: vscode.ExtensionContext, firstTimeRun: boolean
     context.globalState.update(KEY_IS_WELCOME_PAGE_VIEWED, !firstTimeRun);
 };
 
-const fetchInitProps = (context: vscode.ExtensionContext) => {
-    const walkthrough = isWalkthroughEnabled();
+const fetchInitProps = async (context: vscode.ExtensionContext) => {
+    const walkthrough = await isWalkthroughEnabled();
     welcomeView?.webview.postMessage({
         command: "onDidFetchInitProps",
         props: {
@@ -99,8 +99,8 @@ const fetchInitProps = (context: vscode.ExtensionContext) => {
     setFirstTimeRun(context, false);
 };
 
-const showTourPage = (context: vscode.ExtensionContext) => {
-    const walkthrough = isWalkthroughEnabled();
+const showTourPage = async (context: vscode.ExtensionContext) => {
+    const walkthrough = await isWalkthroughEnabled();
     welcomeView?.webview.postMessage({
         command: "onDidFetchInitProps",
         props: {