fix: avoid activating Java during debug configuration discovery

Author: wenytang-ms

README.md

@@ -62,6 +62,8 @@ The debugger will automatically attach. See [No-Config Debug Documentation](bund
 
 No-Config Debug is enabled by default. To disable the terminal integration and the AI `debug_java_application` tool, set `"java.debug.settings.enableNoConfigDebug": false`, reload VS Code, and recreate existing terminals. Standard Java launch/attach debugging, including F5 and Run/Debug CodeLens, remains available.
 
+Preparing the terminal integration does not start or wait for the Java language extension. The wrapper uses `JAVA_HOME`, then `VSCODE_JAVA_EXEC` when available, then `java` on `PATH`. If Java support activates later, recreate an existing terminal to use the newly discovered Java executable.
+
 ## AI-Assisted Debugging
 
 When using GitHub Copilot Chat, you can now ask AI to help you debug Java applications! The extension provides a Language Model Tool that enables natural language debugging:

bundled/scripts/noConfigScripts/README.md

@@ -11,6 +11,10 @@ When you open a terminal in VS Code with this extension installed, the following
 
 Note: `JAVA_TOOL_OPTIONS` is NOT set globally to avoid affecting other Java tools (javac, maven, gradle). Instead, it's set only when you run the `debugjava` command.
 
+Terminal setup does not activate or wait for Language Support for Java. Opening the debug configuration picker in a non-Java workspace therefore does not start Java just to discover its executable. If Java support is already active, its tooling JDK is contributed as `VSCODE_JAVA_EXEC`; otherwise, the integration observes activation in the background and adds it when available. Observation stops after activation or when the integration is disposed.
+
+The wrapper keeps its selection order: `JAVA_HOME`, then `VSCODE_JAVA_EXEC`, then `java` on `PATH`. An existing cached `VSCODE_JAVA_EXEC` is retained while Java support is unavailable. Terminals created before Java executable discovery must be recreated to receive the new value. Actual Java launch/attach still requires Java support and may activate it.
+
 ## Disabling No-Config Debug
 
 No-Config Debug is enabled by default. To opt out for all workspaces or just the current workspace, add this to the corresponding VS Code settings:

src/extension.ts

@@ -31,7 +31,6 @@ import { initializeThreadOperations } from "./threadOperations";
 import * as utility from "./utility";
 import { registerBreakpointCommands } from "./breakpointCommands";
 import { registerVariableMenuCommands } from "./variableMenu";
-import { promisify } from "util";
 
 export async function activate(context: vscode.ExtensionContext): Promise<any> {
     await initializeFromJsonFile(context.asAbsolutePath("./package.json"));
@@ -97,7 +96,7 @@ function initializeExtension(_operationId: string, context: vscode.ExtensionCont
     initializeHotCodeReplace(context);
     initializeCodeLensProvider(context);
     initializeThreadOperations(context);
-    subscribeToJavaExtensionEvents();
+    subscribeToJavaExtensionEvents(context);
 
     context.subscriptions.push(vscode.languages.registerInlineValuesProvider("java", new JavaInlineValuesProvider()));
     return {
@@ -110,8 +109,6 @@ export async function deactivate() {
     await disposeTelemetryWrapper();
 }
 
-const delay = promisify(setTimeout);
-
 /**
  * Register Language Model Tools after Java Language Server is ready.
  * The debug tools depend on JDT.LS for compilation, classpath resolution,
@@ -157,22 +154,11 @@ async function registerLanguageModelToolsWhenReady(context: vscode.ExtensionCont
     }
 }
 
-async function subscribeToJavaExtensionEvents(): Promise<void> {
-    const javaExt = vscode.extensions.getExtension("redhat.java");
-    if (!javaExt) {
-       return;
-    }
-
-    // wait javaExt to activate
-    const timeout = 30 * 60 * 1000; // wait 30 min at most
-    let count = 0;
-    while (!javaExt.isActive && count < timeout) {
-       await delay(1000);
-       count += 1000;
-    }
-
-    if (javaExt.isActive) {
-        javaExt.exports?.onDidSourceInvalidate?.((event: any) => {
+function subscribeToJavaExtensionEvents(context: vscode.ExtensionContext): void {
+    context.subscriptions.push(utility.onDidActivateJavaExtension((api: {
+        onDidSourceInvalidate?: vscode.Event<{ affectedRootPaths?: string[] }>;
+    } | undefined) => {
+        const subscription = api?.onDidSourceInvalidate?.((event) => {
             if (event?.affectedRootPaths?.length) {
                 const activeDebugSession = vscode.debug.activeDebugSession;
                 if (activeDebugSession?.type === "java") {
@@ -182,7 +168,10 @@ async function subscribeToJavaExtensionEvents(): Promise<void> {
                 }
             }
         });
-    }
+        if (subscription) {
+            context.subscriptions.push(subscription);
+        }
+    }));
 }
 
 function registerDebugEventListener(context: vscode.ExtensionContext) {

src/noConfigDebugInit.ts

@@ -6,7 +6,7 @@ import * as path from 'path';
 import * as vscode from 'vscode';
 
 import { sendInfo, sendError } from "vscode-extension-telemetry-wrapper";
-import { getJavaHome } from "./utility";
+import { onDidActivateJavaExtension } from "./utility";
 import { buildNoConfigPathAppendValue } from "./pathUtil";
 import { applyAppendIfChanged, applyReplaceIfChanged } from "./envVarSync";
 
@@ -237,7 +237,7 @@ export async function registerNoConfigDebug(
         });
     };
 
-    // Listen before publishing the endpoint or awaiting Java/script setup.
+    // Listen before publishing the endpoint or awaiting script setup.
     // Terminals surviving a reload may already have the stable endpoint path.
     const fileCreationEvent = fileSystemWatcher.onDidCreate(handleEndpointFile);
     const fileChangeEvent = fileSystemWatcher.onDidChange(handleEndpointFile);
@@ -267,21 +267,6 @@ export async function registerNoConfigDebug(
     // only in the debugjava wrapper scripts (debugjava.ps1, debugjava.bat, debugjava)
     applyReplaceIfChanged(collection, 'VSCODE_JDWP_ADAPTER_ENDPOINTS', tempFilePath);
 
-    // Try to get Java executable from Java Language Server
-    // This ensures we use the same Java version as the project is compiled with.
-    // If detection fails or returns nothing, we deliberately keep any previously
-    // set VSCODE_JAVA_EXEC to avoid churn from transient startup failures.
-    try {
-        const javaHome = await getJavaHome();
-        if (javaHome) {
-            const javaExec = path.join(javaHome, 'bin', 'java');
-            applyReplaceIfChanged(collection, 'VSCODE_JAVA_EXEC', javaExec);
-        }
-    } catch (error) {
-        // If we can't get Java from Language Server, that's okay
-        // The wrapper script will fall back to JAVA_HOME or PATH
-    }
-
     const noConfigScriptsDir = path.join(extPath, 'bundled', 'scripts', 'noConfigScripts');
     const debugJavaScriptPath = path.join(noConfigScriptsDir, "debugjava");
     try {
@@ -294,9 +279,16 @@ export async function registerNoConfigDebug(
         sendError(error);
     }
     applyAppendIfChanged(collection, 'PATH', buildNoConfigPathAppendValue(noConfigScriptsDir));
+    const javaExecutableSync = onDidActivateJavaExtension((api: { javaRequirement?: { java_home?: string } } | undefined) => {
+        const javaHome = api?.javaRequirement?.java_home;
+        if (javaHome) {
+            applyReplaceIfChanged(collection, "VSCODE_JAVA_EXEC", path.join(javaHome, "bin", "java"));
+        }
+    });
 
     return Promise.resolve(
         new vscode.Disposable(() => {
+            javaExecutableSync.dispose();
             fileSystemWatcher.dispose();
             fileCreationEvent.dispose();
             fileChangeEvent.dispose();

src/stackTraceLinkProvider.ts

@@ -2,12 +2,12 @@
 // Licensed under the MIT license.
 
 import { CancellationToken, commands, DocumentLink, DocumentLinkProvider, DocumentSelector,
-    env, ExtensionContext, languages, Position, ProviderResult, Range, TextDocument, Uri,
+    env, Event, ExtensionContext, languages, Position, ProviderResult, Range, TextDocument, Uri,
     window, workspace } from "vscode";
 import { instrumentOperationAsVsCodeCommand, sendInfo } from "vscode-extension-telemetry-wrapper";
 import { resolveSourceUri } from "./languageServerPlugin";
 import { parseJavaStackFrame } from "./stackFrameParser";
-import { getJavaExtensionAPI, isJavaExtEnabled, ServerMode } from "./utility";
+import { onDidActivateJavaExtension, ServerMode } from "./utility";
 
 const ANALYZE_STACK_TRACE_COMMAND = "java.debug.analyzeStackTrace";
 const NAVIGATE_TO_STACK_FRAME_COMMAND = "_java.debug.navigateToStackFrame";
@@ -177,16 +177,14 @@ export function registerStackTraceLinkProvider(context: ExtensionContext): void
 }
 
 function registerLinkProviderWhenReady(context: ExtensionContext): void {
-    // Without the Java language server, frames cannot be resolved to source - nothing to linkify.
-    if (!isJavaExtEnabled()) {
-        return;
-    }
-
     const doRegister = () => context.subscriptions.push(
         languages.registerDocumentLinkProvider(STACK_TRACE_DOCUMENT_SELECTOR, new JavaStackTraceLinkProvider()),
     );
 
-    getJavaExtensionAPI().then((api) => {
+    context.subscriptions.push(onDidActivateJavaExtension((api: {
+        serverMode: string;
+        onDidServerModeChange: Event<string>;
+    } | undefined) => {
         if (!api) {
             return;
         }
@@ -205,5 +203,5 @@ function registerLinkProviderWhenReady(context: ExtensionContext): void {
             // Already in Standard mode.
             doRegister();
         }
-    });
+    }));
 }

src/utility.ts

@@ -177,19 +177,69 @@ export function getJavaExtensionAPI(progressReporter?: IProgressReporter): Thena
         throw new JavaExtensionNotEnabledError("VS Code Java Extension is not enabled.");
     }
 
-    return new Promise<any>(async (resolve) => {
-        progressReporter?.getCancellationToken().onCancellationRequested(() => {
-            resolve(undefined);
-        });
+    const token = progressReporter?.getCancellationToken();
+    if (token?.isCancellationRequested) {
+        return Promise.resolve(undefined);
+    }
 
-        resolve(await extension.activate());
-    });
+    const activation = extension.activate();
+    if (!token) {
+        return activation;
+    }
+
+    let listener: vscode.Disposable | undefined;
+    return Promise.race([
+        activation,
+        new Promise<undefined>((resolve) => {
+            listener = token.onCancellationRequested(() => resolve(undefined));
+        }),
+    ]).finally(() => listener?.dispose());
 }
 
 export function getJavaExtension(): vscode.Extension<any> | undefined {
     return vscode.extensions.getExtension(JAVA_EXTENSION_ID);
 }
 
+export function onDidActivateJavaExtension<T>(listener: (api: T) => void): vscode.Disposable {
+    let disposed = false;
+    let timer: NodeJS.Timeout | undefined;
+    const update = (): boolean => {
+        if (disposed) {
+            return true;
+        }
+        try {
+            const extension = vscode.extensions.getExtension<T>(JAVA_EXTENSION_ID);
+            if (!extension?.isActive) {
+                return false;
+            }
+            listener(extension.exports);
+        } catch {
+            sendError({
+                name: "JavaExtensionError",
+                message: "Could not initialize integration with the active Java extension.",
+            });
+        }
+        return true;
+    };
+
+    // VS Code has no extension-activation event. Observe without activating Java,
+    // including when the first Java file is opened much later in this workspace.
+    if (!update()) {
+        timer = setInterval(() => {
+            if (update()) {
+                clearInterval(timer);
+            }
+        }, 1000);
+        timer.unref();
+    }
+    return new vscode.Disposable(() => {
+        disposed = true;
+        if (timer) {
+            clearInterval(timer);
+        }
+    });
+}
+
 export function isJavaExtEnabled(): boolean {
     const javaExt = vscode.extensions.getExtension(JAVA_EXTENSION_ID);
     return !!javaExt;