`-w` doesn't work when there are no windows open (fixes #4150)

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

@@ -12,6 +12,7 @@ import {assign} from 'vs/base/common/objects';
 import platform = require('vs/base/common/platform');
 import env = require('vs/workbench/electron-main/env');
 import windows = require('vs/workbench/electron-main/windows');
+import window = require('vs/workbench/electron-main/window');
 import lifecycle = require('vs/workbench/electron-main/lifecycle');
 import menu = require('vs/workbench/electron-main/menus');
 import settings = require('vs/workbench/electron-main/settings');
@@ -28,20 +29,22 @@ export class LaunchService {
 		env.log('Received data from other instance', args);
 
 		let killOtherInstance = args.waitForWindowClose;
+		let usedWindows: window.VSCodeWindow[];
 
 		// Otherwise handle in windows manager
 		if (!!args.extensionDevelopmentPath) {
 			windows.manager.openPluginDevelopmentHostWindow({ cli: args, userEnv: userEnv });
 		} else if (args.pathArguments.length === 0 && args.openNewWindow) {
-			windows.manager.open({ cli: args, userEnv: userEnv, forceNewWindow: true, forceEmpty: true });
+			usedWindows = windows.manager.open({ cli: args, userEnv: userEnv, forceNewWindow: true, forceEmpty: true });
 		} else if (args.pathArguments.length === 0) {
-			windows.manager.focusLastActive(args);
+			usedWindows = [windows.manager.focusLastActive(args)];
 		} else {
-			let usedWindows = windows.manager.open({ cli: args, userEnv: userEnv, forceNewWindow: args.waitForWindowClose || args.openNewWindow, preferNewWindow: !args.openInSameWindow });
+			usedWindows = windows.manager.open({ cli: args, userEnv: userEnv, forceNewWindow: args.waitForWindowClose || args.openNewWindow, preferNewWindow: !args.openInSameWindow });
+		}
 
 		// If the other instance is waiting to be killed, we hook up a window listener if one window
 		// is being used and kill the other instance when that window is being closed
-			if (args.waitForWindowClose && usedWindows && usedWindows.length === 1) {
+		if (args.waitForWindowClose && usedWindows && usedWindows.length === 1 && usedWindows[0]) {
 			let windowToObserve = usedWindows[0];
 			killOtherInstance = false; // only scenario where the "-w" switch is supported and makes sense
 
@@ -52,7 +55,6 @@ export class LaunchService {
 				}
 			});
 		}
-		}
 
 		if (killOtherInstance) {
 			process.kill(otherInstancePid);

src/vs/workbench/electron-main/windows.ts

@@ -964,17 +964,19 @@ export class WindowsManager {
 		});
 	}
 
-	public focusLastActive(cli: env.ICommandLineArguments): void {
+	public focusLastActive(cli: env.ICommandLineArguments): window.VSCodeWindow {
 		let lastActive = this.getLastActiveWindow();
 		if (lastActive) {
 			lastActive.focus();
+
+			return lastActive;
 		}
 
 		// No window - open new one
-		else {
 		this.windowsState.openedFolders = []; // make sure we do not open too much
-			this.open({ cli: cli });
-		}
+		const res = this.open({ cli: cli });
+
+		return res && res[0];
 	}
 
 	public getLastActiveWindow(): window.VSCodeWindow {