Add registerWindowTitleVariable command

src/vs/workbench/browser/parts/titlebar/titlebarPart.ts

@@ -182,10 +182,12 @@ export class BrowserTitleService extends MultiWindowParts<BrowserTitlebarPart> i
 	private variables: ITitleVariable[] = [];
 
 	registerVariables(variables: ITitleVariable[]): void {
-		this.variables.push(...variables);
+		const unregisteredVariables = variables.filter(v => !this.variables.some(v2 => v2.contextKey === v.contextKey));
+
+		this.variables.push(...unregisteredVariables);
 
 		for (const part of this.parts) {
-			part.registerVariables(variables);
+			part.registerVariables(unregisteredVariables);
 		}
 	}
 

src/vs/workbench/contrib/windowTitle/browser/windowTitle.contribution.ts

@@ -0,0 +1,11 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+import { CommandsRegistry } from 'vs/platform/commands/common/commands';
+import { InstantiationType, registerSingleton } from 'vs/platform/instantiation/common/extensions';
+import { IWindowTitleVariableService, registerWindowTitleVariable, WindowTitleVariableService } from 'vs/workbench/contrib/windowTitle/browser/windowTitleVariableService';
+
+registerSingleton(IWindowTitleVariableService, WindowTitleVariableService, InstantiationType.Delayed);
+
+CommandsRegistry.registerCommand('registerWindowTitleVariable', registerWindowTitleVariable);

src/vs/workbench/contrib/windowTitle/browser/windowTitleVariableService.ts

@@ -0,0 +1,47 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+import { IContextKey, IContextKeyService } from 'vs/platform/contextkey/common/contextkey';
+import { createDecorator, ServicesAccessor } from 'vs/platform/instantiation/common/instantiation';
+import { ITitleService } from 'vs/workbench/services/title/browser/titleService';
+import { Disposable } from 'vs/base/common/lifecycle';
+
+export interface IWindowTitleVariableService {
+	readonly _serviceBrand: undefined;
+	setVariable(key: string, value: string): void;
+}
+
+export const IWindowTitleVariableService = createDecorator<IWindowTitleVariableService>('windowTitleVariableService');
+
+export class WindowTitleVariableService extends Disposable implements IWindowTitleVariableService {
+	declare readonly _serviceBrand: undefined;
+	private readonly _contextKeyMap = new Map<string, IContextKey<string>>();
+
+	constructor(
+		@IContextKeyService private readonly contextKeyService: IContextKeyService,
+		@ITitleService private readonly titleService: ITitleService
+	) {
+		super();
+	}
+
+	setVariable(key: string, value: string): void {
+		const prefixedKey = `windowTitleVariable.${key}`;
+
+		let contextKey = this._contextKeyMap.get(prefixedKey);
+		if (!contextKey) {
+			contextKey = this.contextKeyService.createKey(prefixedKey, value);
+			this._contextKeyMap.set(prefixedKey, contextKey);
+			this.titleService.registerVariables([
+				{ name: prefixedKey, contextKey: prefixedKey }
+			]);
+		} else {
+			contextKey.set(value);
+		}
+	}
+}
+
+export function registerWindowTitleVariable(accessor: ServicesAccessor, key: string, value: string) {
+	const windowTitleVariableService = accessor.get(IWindowTitleVariableService);
+	windowTitleVariableService.setVariable(key, value);
+}

src/vs/workbench/workbench.common.main.ts

@@ -397,4 +397,7 @@ import 'vs/workbench/contrib/accountEntitlements/browser/accountsEntitlements.co
 
 // Synchronized Scrolling
 import 'vs/workbench/contrib/scrollLocking/browser/scrollLocking.contribution';
+
+// Window Title
+import 'vs/workbench/contrib/windowTitle/browser/windowTitle.contribution';
 //#endregion