Add java.import.mode setting for on-demand project import

Adds the `java.import.mode` setting with "full" (default) and "ondemand"
values.
In on-demand mode, projects are imported lazily when a Java file is
opened
instead of importing everything at startup.

The import mode is also passed as a JVM arg (-Djdt.ls.importMode) so
JDT-LS
can read it early in plugin startup, before LSP initializationOptions
are
available. This allows skipping waitForProjectRegistryRefreshJob in
on-demand
mode to avoid refreshing stale projects from a previous crashed session.

Signed-off-by: azerr <azerr@redhat.com>

Author: angelozerr

package.json

@@ -503,6 +503,21 @@
         "title": "Project Import/Update",
         "order": 20,
         "properties": {
+          "java.import.mode": {
+            "type": "string",
+            "enum": [
+              "full",
+              "ondemand"
+            ],
+            "enumDescriptions": [
+              "All projects are imported at startup.",
+              "Projects are imported lazily when a file is opened."
+            ],
+            "default": "full",
+            "markdownDescription": "Controls how projects are imported into the workspace.\n- `full`: all projects are discovered and imported at startup (default). Safe and well-tested, but slow for large workspaces.\n- `ondemand`: projects are imported lazily when the user first opens a file belonging to that module. This drastically reduces startup time and memory usage for large multi-module workspaces (e.g. Quarkus with 1300+ modules).",
+            "scope": "window",
+            "order": 5
+          },
           "java.import.projectSelection": {
             "type": "string",
             "enum": [

src/extension.ts

@@ -758,28 +758,34 @@ async function startStandardServer(
 }
 
 async function doStartStandardServer(context: ExtensionContext, requirements: requirements.RequirementsData, clientOptions: LanguageClientOptions, workspacePath: string, triggeredByCommand: boolean = false): Promise<LanguageClient | undefined> {
-	const selector: BuildFileSelector = new BuildFileSelector(context, []);
-	const importMode: ImportMode = await getImportMode(context, selector);
-	if (importMode === ImportMode.automatic) {
-		if (!await ensureNoBuildToolConflicts(context, clientOptions)) {
-			return undefined;
-		}
-	} else {
-		const buildFiles: string[] = [];
-		if (importMode === ImportMode.manual) {
-			const cache = context.workspaceState.get<string[]>(PICKED_BUILD_FILES);
-			if (cache === undefined || cache.length === 0 && triggeredByCommand) {
-				buildFiles.push(...await selector.selectBuildFiles() || []);
-			} else {
-				buildFiles.push(...cache);
+	// In on-demand mode, the build tool is determined by the file being opened
+	// (each importer tries its own build file lookup), so no upfront project
+	// selection or build tool conflict prompt is needed.
+	const javaImportMode = getJavaConfiguration().get<string>("import.mode", "full");
+	if (javaImportMode !== "ondemand") {
+		const selector: BuildFileSelector = new BuildFileSelector(context, []);
+		const importMode: ImportMode = await getImportMode(context, selector);
+		if (importMode === ImportMode.automatic) {
+			if (!await ensureNoBuildToolConflicts(context, clientOptions)) {
+				return undefined;
 			}
+		} else {
+			const buildFiles: string[] = [];
+			if (importMode === ImportMode.manual) {
+				const cache = context.workspaceState.get<string[]>(PICKED_BUILD_FILES);
+				if (cache === undefined || cache.length === 0 && triggeredByCommand) {
+					buildFiles.push(...await selector.selectBuildFiles() || []);
+				} else {
+					buildFiles.push(...cache);
+				}
+			}
+			if (buildFiles.length === 0) {
+				commands.executeCommand('setContext', 'java:serverMode', ServerMode.lightWeight);
+				serverStatusBarProvider.showNotImportedStatus();
+				return undefined;
+			}
+			clientOptions.initializationOptions.projectConfigurations = buildFiles;
 		}
-		if (buildFiles.length === 0) {
-			commands.executeCommand('setContext', 'java:serverMode', ServerMode.lightWeight);
-			serverStatusBarProvider.showNotImportedStatus();
-			return undefined;
-		}
-		clientOptions.initializationOptions.projectConfigurations = buildFiles;
 	}
 
 	if (apiManager.getApiInstance().serverMode === ServerMode.lightWeight) {
@@ -789,7 +795,13 @@ async function doStartStandardServer(context: ExtensionContext, requirements: re
 	}
 	await standardClient.initialize(context, requirements, clientOptions, workspacePath, jdtEventEmitter);
 	standardClient.start().then(async () => {
-		standardClient.registerLanguageClientActions(context, await fse.pathExists(path.join(workspacePath, ".metadata", ".plugins")), jdtEventEmitter);
+		// Register handlers immediately (no await before) so they are ready
+		// when the server sends synchronizeBundles and ServiceReady right after 'initialized'.
+		// In on-demand mode with no Java file open, zero projects are loaded at startup,
+		// so the server reaches synchronizeBundles so fast that an await here would cause
+		// the ExecuteClientCommandRequest handler to not be registered in time.
+		const hasImportedPromise = fse.pathExists(path.join(workspacePath, ".metadata", ".plugins"));
+		standardClient.registerLanguageClientActions(context, hasImportedPromise, jdtEventEmitter);
 		// Send auto-detected JDKs after server startup to avoid blocking initialization
 		standardClient.getClient().sendNotification(DidChangeConfigurationNotification.type, {
 			settings: {

src/javaServerStarter.ts

@@ -266,6 +266,16 @@ function prepareParams(requirements: RequirementsData, workspacePath, context: E
 	if (vmargs.indexOf('-DDetectVMInstallationsJob.disabled=') < 0) {
 		params.push('-DDetectVMInstallationsJob.disabled=true');
 	}
+	// Pass import mode as JVM arg so JDT-LS can read it early in plugin startup,
+	// before LSP initializationOptions are available. This allows skipping
+	// waitForProjectRegistryRefreshJob in on-demand mode to avoid refreshing
+	// stale projects from a previous crashed session.
+	if (vmargs.indexOf('-Djdt.ls.importMode=') < 0) {
+		const importMode = getJavaConfiguration().get<string>('import.mode', 'full');
+		if (importMode !== 'full') {
+			params.push(`-Djdt.ls.importMode=${importMode}`);
+		}
+	}
 	const encodingKey = '-Dfile.encoding=';
 	if (vmargs.indexOf(encodingKey) < 0) {
 		params.push(encodingKey + getJavaEncoding());

src/standardLanguageClient.ts

@@ -118,7 +118,7 @@ export class StandardLanguageClient {
 		this.status = ClientStatus.initialized;
 	}
 
-	public registerLanguageClientActions(context: ExtensionContext, hasImported: boolean, jdtEventEmitter: EventEmitter<Uri>) {
+	public registerLanguageClientActions(context: ExtensionContext, hasImportedPromise: Promise<boolean>, jdtEventEmitter: EventEmitter<Uri>) {
 		activationProgressNotification.showProgress();
 		this.languageClient.onNotification(StatusNotification.type, async (report) => {
 			// Resolve serverRunning on the first status notification from the server,
@@ -142,6 +142,7 @@ export class StandardLanguageClient {
 						logger.error(error);
 					}
 					activationProgressNotification.hide();
+					const hasImported = await hasImportedPromise;
 					if (!hasImported) {
 						showImportFinishNotification(context);
 					}