Adds a backup method (#88948)

Adds a backup method to the custom editor API proposal. This method allows custom editors to hook in to VS Code's hot exit behavior

If `backup` is not implemented, VS Code will assume that the custom editor cannot be hot exited.

When `backup` is implemented, VS Code will invoke the method after every edit (this is debounced). At this point, this extension should back up the current resource.  The result is a promise indicating if the backup was successful or not

VS Code will only hot exit if all backups were successful.

src/vs/workbench/api/browser/mainThreadWebview.ts

@@ -3,6 +3,7 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
+import { createCancelablePromise } from 'vs/base/common/async';
 import { onUnexpectedError } from 'vs/base/common/errors';
 import { Disposable, DisposableStore, IDisposable } from 'vs/base/common/lifecycle';
 import { Schemas } from 'vs/base/common/network';
@@ -355,7 +356,10 @@ export class MainThreadWebviews extends Disposable implements extHostProtocol.Ma
 		});
 
 		if (capabilitiesSet.has(extHostProtocol.WebviewEditorCapabilities.SupportsHotExit)) {
-			// TODO: Hook up hot exit / backup logic
+			model.onBackup(() => {
+				return createCancelablePromise(token =>
+					this._proxy.$backup(model.resource.toJSON(), viewType, token));
+			});
 		}
 
 		return model;

src/vs/workbench/api/common/extHost.protocol.ts

@@ -612,6 +612,8 @@ export interface ExtHostWebviewsShape {
 
 	$onSave(resource: UriComponents, viewType: string): Promise<void>;
 	$onSaveAs(resource: UriComponents, viewType: string, targetResource: UriComponents): Promise<void>;
+
+	$backup(resource: UriComponents, viewType: string, cancellation: CancellationToken): Promise<boolean>;
 }
 
 export interface MainThreadUrlsShape extends IDisposable {

src/vs/workbench/api/common/extHostWebview.ts

@@ -18,6 +18,7 @@ import type * as vscode from 'vscode';
 import { Cache } from './cache';
 import { ExtHostWebviewsShape, IMainContext, MainContext, MainThreadWebviewsShape, WebviewEditorCapabilities, WebviewPanelHandle, WebviewPanelViewStateData } from './extHost.protocol';
 import { Disposable as VSCodeDisposable } from './extHostTypes';
+import { CancellationToken } from 'vs/base/common/cancellation';
 
 type IconPath = URI | { light: URI, dark: URI };
 
@@ -478,6 +479,14 @@ export class ExtHostWebviews implements ExtHostWebviewsShape {
 		return provider?.editingDelegate?.saveAs(URI.revive(resource), URI.revive(targetResource));
 	}
 
+	async $backup(resource: UriComponents, viewType: string, cancellation: CancellationToken): Promise<boolean> {
+		const provider = this.getEditorProvider(viewType);
+		if (!provider?.editingDelegate?.backup) {
+			return false;
+		}
+		return provider.editingDelegate.backup(URI.revive(resource), cancellation);
+	}
+
 	private getWebviewPanel(handle: WebviewPanelHandle): ExtHostWebviewEditor | undefined {
 		return this._webviewPanels.get(handle);
 	}
@@ -491,6 +500,9 @@ export class ExtHostWebviews implements ExtHostWebviewsShape {
 		if (capabilities.editingDelegate) {
 			declaredCapabilites.push(WebviewEditorCapabilities.Editable);
 		}
+		if (capabilities.editingDelegate?.backup) {
+			declaredCapabilites.push(WebviewEditorCapabilities.SupportsHotExit);
+		}
 		return declaredCapabilites;
 	}
 }