Only register the reticulate runtime manager when at least one R runt…

…ime exists.

extensions/positron-reticulate/src/extension.ts

@@ -406,15 +406,78 @@ class ReticulateRuntimeMetadata implements positron.LanguageRuntimeMetadata {
 
 export class ReticulateProvider {
 	_client: positron.RuntimeClientInstance | undefined = undefined;
-	constructor(readonly manager: ReticulateRuntimeManager) { }
+	manager: ReticulateRuntimeManager | undefined;
+	registrationHook: vscode.Disposable | undefined;
+
+	constructor(readonly context: vscode.ExtensionContext) {
+		// Check if the reticulate runtime manager has been registered before
+		// in this workspace. If it happened, we register the reticulate manager
+		// automatically, no need to wait for R.
+		if (this.context.workspaceState.get<boolean>('reticulate_registered', false)) {
+			this.registerReticulateRuntimeManager();
+		} else {
+			// Launch an async task that might register the reticulate runtime manager
+			// if conditions are match.
+			this.maybeRegisterReticulateManager();
+		}
+	}
+
+	async maybeRegisterReticulateManager() {
+		// Get a fixed list of all current runtimes.
+		const runtimes = await positron.runtime.getRegisteredRuntimes();
+
+		// Hook that will register the reticulate runtime if an R
+		// runtime is found.
+		this.registrationHook = positron.runtime.onDidRegisterRuntime((metadata) => {
+			if (!this.manager && metadata.languageId === 'r') {
+				this.registerReticulateRuntimeManager();
+			}
+		});
+
+		this.context.subscriptions.push(this.registrationHook);
+
+		// Walk trough the list of runtimes looking for an R runtime,
+		// if one exists we register the reticulate runtime manager.
+		// We also dispose the above hook if we get to register the
+		// runtime.
+		for (const runtime of runtimes) {
+			if (!this.manager && runtime.languageId === 'r') {
+				this.registerReticulateRuntimeManager();
+				return;
+			}
+		}
+	}
+
+	registerReticulateRuntimeManager() {
+		this.manager = new ReticulateRuntimeManager(this.context);
+		this.context.subscriptions.push(positron.runtime.registerLanguageRuntimeManager(this.manager));
+
+		// Dispose the registration hook so we don't keep checking for new runtimes
+		// once we already registered ours.
+		if (this.registrationHook) {
+			this.registrationHook.dispose();
+			this.registrationHook = undefined;
+		}
+
+		// Once the reticulate manager has been registered, we store a project flag that will
+		// always load the manager later on.
+		this.context.workspaceState.update('reticulate_registered', true);
+	}
 
 	async registerClient(client: positron.RuntimeClientInstance) {
 		if (this._client) {
 			this._client.dispose();
 		}
+
 		this._client = client;
 
-		await this.manager.discoverRuntimes();
+		if (!this.manager) {
+			// No ReticulateRuntimeManager!
+			// We won't be able to start the reticulate sesssion.
+			console.error('No reticulate runtime manager. We will not be able to start the reticulate session.');
+			return;
+		}
+
 		await positron.runtime.selectLanguageRuntime('reticulate');
 
 		this.manager._session?.onDidEndSession(() => {
@@ -462,11 +525,7 @@ let CONTEXT: vscode.ExtensionContext;
  */
 export function activate(context: vscode.ExtensionContext) {
 	CONTEXT = context;
-
-	const manager = new ReticulateRuntimeManager(context);
-	context.subscriptions.push(positron.runtime.registerLanguageRuntimeManager(manager));
-
-	const reticulateProvider = new ReticulateProvider(manager);
+	const reticulateProvider = new ReticulateProvider(context);
 
 	context.subscriptions.push(
 		positron.runtime.registerClientHandler({
@@ -479,6 +538,6 @@ export function activate(context: vscode.ExtensionContext) {
 
 	context.subscriptions.push(reticulateProvider);
 
-	return manager;
+	return reticulateProvider;
 }