First attempt

src/vs/code/electron-main/menus.ts

@@ -31,6 +31,9 @@ interface IConfiguration extends IFilesConfiguration {
 		},
 		statusBar: {
 			visible: boolean;
+		},
+		activityBar: {
+			visible: boolean;
 		}
 	};
 }
@@ -44,6 +47,7 @@ export class VSCodeMenu {
 	private currentAutoSaveSetting: string;
 	private currentSidebarLocation: 'left' | 'right';
 	private currentStatusbarVisible: boolean;
+	private currentActivityBarVisible: boolean;
 
 	private isQuitting: boolean;
 	private appMenuInstalled: boolean;
@@ -151,6 +155,15 @@ export class VSCodeMenu {
 				this.currentStatusbarVisible = newStatusbarVisible;
 				updateMenu = true;
 			}
+
+			let newActivityBarVisible = config.workbench.activityBar && config.workbench.activityBar.visible;
+			if (typeof newActivityBarVisible !== 'boolean') {
+				newActivityBarVisible = true;
+			}
+			if (newActivityBarVisible !== this.currentActivityBarVisible) {
+				this.currentActivityBarVisible = newActivityBarVisible;
+				updateMenu = true;
+			}
 		}
 
 		if (handleMenu && updateMenu) {
@@ -543,6 +556,14 @@ export class VSCodeMenu {
 		}
 		const toggleStatusbar = this.createMenuItem(statusBarLabel, 'workbench.action.toggleStatusbarVisibility');
 
+		let activityBarLabel: string;
+		if (this.currentActivityBarVisible) {
+			activityBarLabel = 'Show Activity Bar';
+		} else {
+			activityBarLabel = 'Hide Activity Bar';
+		}
+		const toggleActivtyBar = this.createMenuItem(activityBarLabel, 'workbench.action.toggleActivityBarVisibility');
+
 		const toggleWordWrap = this.createMenuItem(nls.localize({ key: 'miToggleWordWrap', comment: ['&& denotes a mnemonic'] }, "Toggle &&Word Wrap"), 'editor.action.toggleWordWrap');
 		const toggleRenderWhitespace = this.createMenuItem(nls.localize({ key: 'miToggleRenderWhitespace', comment: ['&& denotes a mnemonic'] }, "Toggle &&Render Whitespace"), 'editor.action.toggleRenderWhitespace');
 		const toggleRenderControlCharacters = this.createMenuItem(nls.localize({ key: 'miToggleRenderControlCharacters', comment: ['&& denotes a mnemonic'] }, "Toggle &&Control Characters"), 'editor.action.toggleRenderControlCharacter');
@@ -574,6 +595,7 @@ export class VSCodeMenu {
 			toggleSidebar,
 			togglePanel,
 			toggleStatusbar,
+			toggleActivtyBar,
 			__separator__(),
 			toggleWordWrap,
 			toggleRenderWhitespace,

src/vs/test/utils/servicesTestUtils.ts

@@ -240,6 +240,12 @@ export class TestPartService implements IPartService {
 		return false;
 	}
 
+	public isActivityBarHidden(): boolean {
+		return false;
+	}
+
+	public setActivityBarHidden(hidden: boolean): void { }
+
 	public isSideBarHidden(): boolean {
 		return false;
 	}

src/vs/workbench/browser/actions/toggleActivityBarVisibility.ts

+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+'use strict';
+
+import { TPromise } from 'vs/base/common/winjs.base';
+import nls = require('vs/nls');
+import { Registry } from 'vs/platform/platform';
+import { Action } from 'vs/base/common/actions';
+import { SyncActionDescriptor } from 'vs/platform/actions/common/actions';
+import { IWorkbenchActionRegistry, Extensions } from 'vs/workbench/common/actionRegistry';
+import { IMessageService, Severity } from 'vs/platform/message/common/message';
+import { IConfigurationEditingService, ConfigurationTarget } from 'vs/workbench/services/configuration/common/configurationEditing';
+import { IPartService } from 'vs/workbench/services/part/common/partService';
+
+export class ToggleActivityBarVisibilityAction extends Action {
+
+	public static ID = 'workbench.action.toggleActivityBarVisibility';
+	public static LABEL = nls.localize('toggleActivityBar', "Toggle Activity Bar Visibility");
+
+	private static activityBarVisibleKey = 'workbench.activitybar.visible';
+
+	constructor(
+		id: string,
+		label: string,
+		@IPartService private partService: IPartService,
+		@IMessageService private messageService: IMessageService,
+		@IConfigurationEditingService private configurationEditingService: IConfigurationEditingService
+	) {
+		super(id, label);
+
+		this.enabled = !!this.partService;
+	}
+
+	public run(): TPromise<any> {
+		const visibility = !this.partService.isActivityBarHidden();
+		const newVisibilityValue = !visibility;
+
+		this.configurationEditingService.writeConfiguration(ConfigurationTarget.USER, { key: ToggleActivityBarVisibilityAction.activityBarVisibleKey, value: newVisibilityValue }).then(null, error => {
+			this.messageService.show(Severity.Error, error);
+		});
+
+		return TPromise.as(null);
+	}
+}
+
+let registry = <IWorkbenchActionRegistry>Registry.as(Extensions.WorkbenchActions);
+registry.registerWorkbenchAction(new SyncActionDescriptor(ToggleActivityBarVisibilityAction, ToggleActivityBarVisibilityAction.ID, ToggleActivityBarVisibilityAction.LABEL), 'View: Toggle Activity Bar Visibility', nls.localize('view', "View"));
\ No newline at end of file

src/vs/workbench/browser/layout.ts

@@ -343,6 +343,7 @@ export class WorkbenchLayout implements IVerticalSashLayoutProvider, IHorizontal
 
 		this.workbenchSize = this.getWorkbenchArea();
 
+		const isActivityBarHidden = this.partService.isActivityBarHidden();
 		const isSidebarHidden = this.partService.isSideBarHidden();
 		const isPanelHidden = this.partService.isPanelHidden();
 		const sidebarPosition = this.partService.getSideBarPosition();
@@ -366,7 +367,13 @@ export class WorkbenchLayout implements IVerticalSashLayoutProvider, IHorizontal
 
 		// Activity Bar
 		let activityBarMinWidth = this.computedStyles.activitybar.minWidth;
-		let activityBarSize = new Dimension(activityBarMinWidth, sidebarSize.height);
+		let activityBarWidth: number;
+		if (isActivityBarHidden) {
+			activityBarWidth = 0;
+		} else {
+			activityBarWidth = activityBarMinWidth;
+		}
+		let activityBarSize = new Dimension(activityBarWidth, sidebarSize.height);
 
 		// Panel part
 		let panelHeight: number;
@@ -399,7 +406,7 @@ export class WorkbenchLayout implements IVerticalSashLayoutProvider, IHorizontal
 
 		// Sidebar hidden
 		if (isSidebarHidden) {
-			editorSize.width = Math.min(this.workbenchSize.width - activityBarSize.width, this.workbenchSize.width - activityBarMinWidth);
+			editorSize.width = this.workbenchSize.width - activityBarSize.width;
 
 			if (sidebarPosition === Position.LEFT) {
 				editorSize.remainderLeft = Math.round((this.workbenchSize.width - editorSize.width + activityBarSize.width) / 2);
@@ -531,7 +538,8 @@ export class WorkbenchLayout implements IVerticalSashLayoutProvider, IHorizontal
 	public getVerticalSashLeft(sash: Sash): number {
 		let isSidebarHidden = this.partService.isSideBarHidden();
 		let sidebarPosition = this.partService.getSideBarPosition();
-		let activitybarWidth = this.computedStyles.activitybar.minWidth;
+		let isActivityBarHidden = this.partService.isActivityBarHidden();
+		let activitybarWidth = !isActivityBarHidden ? this.computedStyles.activitybar.minWidth : 0;
 
 		if (sidebarPosition === Position.LEFT) {
 			return !isSidebarHidden ? this.sidebarWidth + activitybarWidth : activitybarWidth;

src/vs/workbench/browser/parts/activitybar/media/activitybarpart.css

@@ -13,6 +13,11 @@
 	height: 100%;
 }
 
+.monaco-workbench.noactivitybar > .activitybar {
+	display: none !important;
+	visibility: hidden !important;
+}
+
 .monaco-workbench > .activitybar > .content .monaco-action-bar {
 	text-align: left;
 	background-color: inherit;

src/vs/workbench/electron-browser/main.contribution.ts

@@ -120,6 +120,11 @@ configurationRegistry.registerConfiguration({
 			'type': 'boolean',
 			'default': true,
 			'description': nls.localize('statusBarVisibility', "Controls the visibility of the status bar at the bottom of the workbench.")
+		},
+		'workbench.activitybar.visible': {
+			'type': 'boolean',
+			'default': true,
+			'description': nls.localize('activityBarVisibility', "Controls the visibility of the activity bar on the left side of the workbench.")
 		}
 	}
 });

src/vs/workbench/electron-browser/workbench.ts

@@ -113,6 +113,8 @@ export class Workbench implements IPartService {
 	private static sidebarPositionConfigurationKey = 'workbench.sideBar.location';
 	private static statusbarVisibleConfigurationKey = 'workbench.statusBar.visible';
 
+	private static activityBarVisibleConfigurationKey = 'workbench.activitybar.visible';
+
 	public _serviceBrand: any;
 
 	private container: HTMLElement;
@@ -140,6 +142,7 @@ export class Workbench implements IPartService {
 	private creationPromiseComplete: ValueCallback;
 	private sideBarHidden: boolean;
 	private statusBarHidden: boolean;
+	private activityBarHidden: boolean;
 	private sideBarPosition: Position;
 	private panelHidden: boolean;
 	private editorBackgroundDelayer: Delayer<void>;
@@ -452,6 +455,11 @@ export class Workbench implements IPartService {
 		// Statusbar visibility
 		const statusBarVisible = this.configurationService.lookup<string>(Workbench.statusbarVisibleConfigurationKey).value;
 		this.statusBarHidden = !statusBarVisible;
+
+		// Activity bar visibility
+		const activityBarVisible = this.configurationService.lookup<string>(Workbench.activityBarVisibleConfigurationKey).value;
+		this.activityBarHidden = !activityBarVisible;
+
 	}
 
 	/**
@@ -512,6 +520,8 @@ export class Workbench implements IPartService {
 				return !this.panelHidden;
 			case Parts.STATUSBAR_PART:
 				return !this.statusBarHidden;
+			case Parts.ACTIVITYBAR_PART:
+				return !this.activityBarHidden;
 		}
 
 		return true; // any other part cannot be hidden
@@ -530,6 +540,26 @@ export class Workbench implements IPartService {
 		}
 	}
 
+	public isActivityBarHidden(): boolean {
+		return this.activityBarHidden;
+	}
+
+	public setActivityBarHidden(hidden: boolean, skipLayout?: boolean): void {
+		this.activityBarHidden = hidden;
+
+		// Adjust CSS
+		if (hidden) {
+			this.workbench.addClass('noactivitybar');
+		} else {
+			this.workbench.removeClass('noactivitybar');
+		}
+
+		// Layout
+		if (!skipLayout) {
+			this.workbenchLayout.layout({ forceStyleReCompute: true });
+		}
+	}
+
 	public isSideBarHidden(): boolean {
 		return this.sideBarHidden;
 	}
@@ -715,6 +745,11 @@ export class Workbench implements IPartService {
 		if (newStatusbarHiddenValue !== this.isStatusBarHidden()) {
 			this.setStatusBarHidden(newStatusbarHiddenValue);
 		}
+
+		const newActivityBarHiddenValue = !this.configurationService.lookup<boolean>(Workbench.activityBarVisibleConfigurationKey).value;
+		if (newActivityBarHiddenValue !== this.isActivityBarHidden()) {
+			this.setActivityBarHidden(newActivityBarHiddenValue);
+		}
 	}
 
 	private createWorkbenchLayout(): void {

src/vs/workbench/services/part/common/partService.ts

@@ -55,6 +55,16 @@ export interface IPartService {
 	 */
 	isVisible(part: Parts): boolean;
 
+	/**
+	 * Checks if the activity bar is currently hidden or not
+	 */
+	isActivityBarHidden(): boolean;
+
+	/**
+	 * Set activity bar hidden or not
+	 */
+	setActivityBarHidden(hidden: boolean): void;
+
 	/**
 	 * Checks if the statusbar is currently hidden or not
 	 */

src/vs/workbench/workbench.main.ts

@@ -20,6 +20,7 @@ import 'vs/editor/browser/editor.all';
 import 'vs/platform/actions/browser/menusExtensionPoint';
 
 // Workbench
+import 'vs/workbench/browser/actions/toggleActivityBarVisibility';
 import 'vs/workbench/browser/actions/toggleStatusbarVisibility';
 import 'vs/workbench/browser/actions/toggleSidebarVisibility';
 import 'vs/workbench/browser/actions/toggleSidebarPosition';