From c2b02df9ab208b025b214599660ee86027ca7df9 Mon Sep 17 00:00:00 2001
From: Matt Bierner <matb@microsoft.com>
Date: Wed, 22 May 2019 15:23:22 -0700
Subject: [PATCH] Allow hidden (but persisted) webviews to recieve messages

Fixes #47534
---
 .../src/singlefolder-tests/webview.test.ts    | 87 +++++++++++--------
 .../api/electron-browser/mainThreadWebview.ts | 17 ++--
 2 files changed, 61 insertions(+), 43 deletions(-)

diff --git a/extensions/vscode-api-tests/src/singlefolder-tests/webview.test.ts b/extensions/vscode-api-tests/src/singlefolder-tests/webview.test.ts
index 5e28b247b07..3cc1cb3863b 100644
--- a/extensions/vscode-api-tests/src/singlefolder-tests/webview.test.ts
+++ b/extensions/vscode-api-tests/src/singlefolder-tests/webview.test.ts
@@ -132,24 +132,7 @@ suite('Webview tests', () => {
 		// Open webview in same column
 		const webview = _register(vscode.window.createWebviewPanel(webviewId, 'title', { viewColumn: vscode.ViewColumn.One }, { enableScripts: true }));
 		const ready = getMesssage(webview);
-		webview.webview.html = createHtmlDocumentWithBody(/*html*/`
-			<script>
-				const vscode = acquireVsCodeApi();
-				let value = 0;
-				window.addEventListener('message', (message) => {
-					switch (message.data.type) {
-						case 'get':
-							vscode.postMessage({ value });
-							break;
-
-						case 'add':
-							++value;;
-							vscode.postMessage({ value });
-							break;
-					}
-				});
-				vscode.postMessage({ type: 'ready' });
-			</script>`);
+		webview.webview.html = statefulWebviewHtml;
 		await ready;
 
 		const firstResponse = await sendRecieveMessage(webview, { type: 'add' });
@@ -167,25 +150,7 @@ suite('Webview tests', () => {
 		const webview = _register(vscode.window.createWebviewPanel(webviewId, 'title', { viewColumn: vscode.ViewColumn.One }, { enableScripts: true, retainContextWhenHidden: true }));
 		const ready = getMesssage(webview);
 
-		webview.webview.html = createHtmlDocumentWithBody(/*html*/`
-			<script>
-				const vscode = acquireVsCodeApi();
-				let value = 0;
-				window.addEventListener('message', (message) => {
-					switch (message.data.type) {
-						case 'get':
-							vscode.postMessage({ value });
-							break;
-
-						case 'add':
-							++value;;
-							vscode.setState({ value });
-							vscode.postMessage({ value });
-							break;
-					}
-				});
-				vscode.postMessage({ type: 'ready' });
-			</script>`);
+		webview.webview.html = statefulWebviewHtml;
 		await ready;
 
 		const firstResponse = await sendRecieveMessage(webview, { type: 'add' });
@@ -244,6 +209,33 @@ suite('Webview tests', () => {
 		assert.strictEqual(secondResponse.value, 100);
 	});
 
+	conditionalTest('webviews with retainContextWhenHidden should be able to recive messages while hidden', async () => {
+		const webview = _register(vscode.window.createWebviewPanel(webviewId, 'title', { viewColumn: vscode.ViewColumn.One }, { enableScripts: true, retainContextWhenHidden: true }));
+		const ready = getMesssage(webview);
+
+		webview.webview.html = statefulWebviewHtml;
+		await ready;
+
+		const firstResponse = await sendRecieveMessage(webview, { type: 'add' });
+		assert.strictEqual((await firstResponse).value, 1);
+
+		// Swap away from the webview
+		const doc = await vscode.workspace.openTextDocument(testDocument);
+		await vscode.window.showTextDocument(doc);
+
+		// Try posting a message to our hidden webview
+		const secondResponse = await sendRecieveMessage(webview, { type: 'add' });
+		assert.strictEqual((await secondResponse).value, 2);
+
+		// Now show webview again
+		webview.reveal(vscode.ViewColumn.One);
+
+		// We should still have old state
+		const thirdResponse = await sendRecieveMessage(webview, { type: 'get' });
+		assert.strictEqual(thirdResponse.value, 2);
+	});
+
+
 	conditionalTest('webviews should only be able to load resources from workspace by default', async () => {
 		const webview = _register(vscode.window.createWebviewPanel(webviewId, 'title', { viewColumn: vscode.ViewColumn.One }, { enableScripts: true }));
 
@@ -356,6 +348,27 @@ function createHtmlDocumentWithBody(body: string): string {
 </html>`;
 }
 
+const statefulWebviewHtml = createHtmlDocumentWithBody(/*html*/ `
+	<script>
+		const vscode = acquireVsCodeApi();
+		let value = 0;
+		window.addEventListener('message', (message) => {
+			switch (message.data.type) {
+				case 'get':
+					vscode.postMessage({ value });
+					break;
+
+				case 'add':
+					++value;;
+					vscode.setState({ value });
+					vscode.postMessage({ value });
+					break;
+			}
+		});
+		vscode.postMessage({ type: 'ready' });
+	</script>`);
+
+
 function getMesssage<R = any>(webview: vscode.WebviewPanel): Promise<R> {
 	return new Promise<R>(resolve => {
 		const sub = webview.webview.onDidReceiveMessage(message => {
diff --git a/src/vs/workbench/api/electron-browser/mainThreadWebview.ts b/src/vs/workbench/api/electron-browser/mainThreadWebview.ts
index 09e372750d1..e0abea919a8 100644
--- a/src/vs/workbench/api/electron-browser/mainThreadWebview.ts
+++ b/src/vs/workbench/api/electron-browser/mainThreadWebview.ts
@@ -210,11 +210,10 @@ export class MainThreadWebviews extends Disposable implements MainThreadWebviews
 		}
 	}
 
-	public $postMessage(handle: WebviewPanelHandle | WebviewInsetHandle, message: any): Promise<boolean> {
+	public async $postMessage(handle: WebviewPanelHandle | WebviewInsetHandle, message: any): Promise<boolean> {
 		if (typeof handle === 'number') {
 			this.getWebviewElement(handle).sendMessage(message);
-			return Promise.resolve(true);
-
+			return true;
 		} else {
 			const webview = this.getWebview(handle);
 			const editors = this._editorService.visibleControls
@@ -222,11 +221,17 @@ export class MainThreadWebviews extends Disposable implements MainThreadWebviews
 				.map(e => e as WebviewEditor)
 				.filter(e => e.input!.matches(webview));
 
-			for (const editor of editors) {
-				editor.sendMessage(message);
+			if (editors.length > 0) {
+				editors[0].sendMessage(message);
+				return true;
 			}
 
-			return Promise.resolve(editors.length > 0);
+			if (webview.webview) {
+				webview.webview.sendMessage(message);
+				return true;
+			}
+
+			return false;
 		}
 	}