Preserve output channel visibility on restart

client-node-tests/src/integration.test.ts

@@ -242,6 +242,52 @@ suite('Server output', () => {
 	});
 });
 
+suite('Client restart', () => {
+
+	test('Preserves output channel visibility after restart', async () => {
+		const client = new RestartTestLanguageClient(true);
+
+		await client.restart();
+
+		assert.deepStrictEqual(client.events, ['isOutputChannelVisible', 'stop', 'start', 'restoreOutputChannelVisibility:true']);
+	});
+
+	test('Does not restore hidden output channel after restart', async () => {
+		const client = new RestartTestLanguageClient(false);
+
+		await client.restart();
+
+		assert.deepStrictEqual(client.events, ['isOutputChannelVisible', 'stop', 'start', 'restoreOutputChannelVisibility:false']);
+	});
+});
+
+class RestartTestLanguageClient extends lsclient.LanguageClient {
+
+	public readonly events: string[] = [];
+
+	public constructor(private readonly outputChannelVisible: boolean) {
+		super('test restart', { module: 'unused', transport: lsclient.TransportKind.ipc }, {});
+	}
+
+	public override async start(): Promise<void> {
+		this.events.push('start');
+	}
+
+	public override stop(): Promise<void> {
+		this.events.push('stop');
+		return Promise.resolve();
+	}
+
+	protected override isOutputChannelVisible(): boolean {
+		this.events.push('isOutputChannelVisible');
+		return this.outputChannelVisible;
+	}
+
+	protected override restoreOutputChannelVisibility(wasVisible: boolean): void {
+		this.events.push(`restoreOutputChannelVisibility:${wasVisible}`);
+	}
+}
+
 suite('Client integration', () => {
 
 	let client!: lsclient.LanguageClient;

client/src/common/client.ts

@@ -858,6 +858,26 @@ export abstract class BaseLanguageClient implements FeatureClient<Middleware, La
 		return this._outputChannel;
 	}
 
+	protected isOutputChannelVisible(): boolean {
+		if (this._outputChannel === undefined) {
+			return false;
+		}
+		const outputChannelName = this._outputChannel.name.toLowerCase();
+		return Window.visibleTextEditors.some(editor => {
+			if (editor.document.uri.scheme !== 'output') {
+				return false;
+			}
+			const outputResource = `${editor.document.uri.toString(true)}\n${editor.document.fileName}`.toLowerCase();
+			return outputResource.includes(outputChannelName);
+		});
+	}
+
+	protected restoreOutputChannelVisibility(wasVisible: boolean): void {
+		if (wasVisible) {
+			this.outputChannel.show(true);
+		}
+	}
+
 	public get traceOutputChannel(): LogOutputChannel {
 		return this._traceOutputChannel ? this._traceOutputChannel : this.outputChannel;
 	}

client/src/node/main.ts

@@ -236,6 +236,7 @@ export class LanguageClient extends BaseLanguageClient {
 	}
 
 	public async restart(): Promise<void> {
+		const outputChannelVisible = this.isOutputChannelVisible();
 		await this.stop();
 		// We are in debug mode. Wait a little before we restart
 		// so that the debug port can be freed. We can safely ignore
@@ -247,6 +248,7 @@ export class LanguageClient extends BaseLanguageClient {
 		} else {
 			await this.start();
 		}
+		this.restoreOutputChannelVisibility(outputChannelVisible);
 	}
 
 	protected shutdown(mode: ShutdownMode, timeout: number = 2000): Promise<void> {