Enable process to write to terminal before the panel exists

Fixes #12000

src/vs/workbench/parts/terminal/electron-browser/terminalInstance.ts

@@ -97,7 +97,9 @@ export class TerminalInstance implements ITerminalInstance {
 		this._onTitleChanged = new Emitter<string>();
 
 		this._createProcess(this._contextService.getWorkspace(), this._shellLaunchConfig);
+		this._createXterm();
 
+		// Only attach xterm.js to the DOM if the terminal panel has been opened before.
 		if (_container) {
 			this.attachToElement(_container);
 		}
@@ -107,21 +109,13 @@ export class TerminalInstance implements ITerminalInstance {
 		this._instanceDisposables.push(disposable);
 	}
 
-	public attachToElement(container: HTMLElement): void {
-		if (this._wrapperElement) {
-			throw new Error('The terminal instance has already been attached to a container');
-		}
-
-		this._container = container;
-		this._wrapperElement = document.createElement('div');
-		DOM.addClass(this._wrapperElement, 'terminal-wrapper');
-		this._xtermElement = document.createElement('div');
-
+	/**
+	 * Create xterm.js instance and attach data listeners.
+	 */
+	protected _createXterm(): void {
 		this._xterm = xterm({
 			scrollback: this._configHelper.getScrollback()
 		});
-		this._xterm.open(this._xtermElement);
-
 		this._process.on('message', (message) => this._sendPtyDataToXterm(message));
 		this._xterm.on('data', (data) => {
 			if (this._process) {
@@ -132,6 +126,19 @@ export class TerminalInstance implements ITerminalInstance {
 			}
 			return false;
 		});
+	}
+
+	public attachToElement(container: HTMLElement): void {
+		if (this._wrapperElement) {
+			throw new Error('The terminal instance has already been attached to a container');
+		}
+
+		this._container = container;
+		this._wrapperElement = document.createElement('div');
+		DOM.addClass(this._wrapperElement, 'terminal-wrapper');
+		this._xtermElement = document.createElement('div');
+
+		this._xterm.open(this._xtermElement);
 		this._xterm.attachCustomKeydownHandler((event: KeyboardEvent) => {
 			// Disable all input if the terminal is exiting
 			if (this._isExiting) {
@@ -387,9 +394,6 @@ export class TerminalInstance implements ITerminalInstance {
 	}
 
 	private _sendPtyDataToXterm(message: { type: string, content: string }): void {
-		if (!this._xterm) {
-			return;
-		}
 		if (message.type === 'data') {
 			this._xterm.write(message.content);
 		}

src/vs/workbench/parts/terminal/test/electron-browser/terminalInstance.test.ts

@@ -25,6 +25,7 @@ class TestTerminalInstance extends TerminalInstance {
 	}
 
 	protected _createProcess(workspace: IWorkspace, shell: IShellLaunchConfig): void { }
+	protected _createXterm(): void { }
 }
 
 suite('Workbench - TerminalInstance', () => {

src/vs/workbench/parts/terminal/test/electron-browser/terminalService.test.ts

@@ -20,7 +20,7 @@ import { TPromise } from 'vs/base/common/winjs.base';
 
 class TestTerminalProcessFactory implements ITerminalProcessFactory {
 	public create(env: { [key: string]: string }): cp.ChildProcess {
-		return <any>{};
+		return <any>{ on: () => { } };
 	}
 }