allow returning undefined if file was not saved

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

@@ -335,7 +335,6 @@ export class ExtHostNotebookController implements ExtHostNotebookShape {
 			throw new files.FileOperationError(localize('err.readonly', "Unable to modify read-only file '{0}'", this._resourceForError(uri)), files.FileOperationResult.FILE_PERMISSION_DENIED);
 		}
 
-
 		const data: vscode.NotebookData = {
 			metadata: filter(document.apiNotebook.metadata, key => !(serializer.options?.transientDocumentMetadata ?? {})[key]),
 			cells: [],
@@ -360,7 +359,15 @@ export class ExtHostNotebookController implements ExtHostNotebookShape {
 		// validate write
 		await this._validateWriteFile(uri, options);
 
+		if (token.isCancellationRequested) {
+			throw new Error('canceled');
+		}
 		const bytes = await serializer.serializer.serializeNotebook(data, token);
+		if (token.isCancellationRequested) {
+			throw new Error('canceled');
+		}
+
+		// Don't accept any cancellation beyond this point, we need to report the result of the file write
 		this.trace(`serialized versionId: ${versionId} ${uri.toString()}`);
 		await this._extHostFileSystem.value.writeFile(uri, bytes);
 		this.trace(`Finished write versionId: ${versionId} ${uri.toString()}`);

src/vs/workbench/services/workingCopy/common/storedFileWorkingCopy.ts

@@ -103,6 +103,18 @@ export interface IStoredFileWorkingCopyModelContentChangedEvent {
 	readonly isRedoing: boolean;
 }
 
+async function optionalIfCancelled<T>(callback: (token: CancellationToken) => Promise<T>, token: CancellationToken): Promise<T | undefined> {
+	try {
+		return await callback(token);
+	} catch (error) {
+		if (token.isCancellationRequested) {
+			return undefined;
+		}
+
+		throw error;
+	}
+}
+
 /**
  * A stored file based `IWorkingCopy` is backed by a `URI` from a
  * known file system provider. Given this assumption, a lot
@@ -1029,7 +1041,11 @@ export class StoredFileWorkingCopy<M extends IStoredFileWorkingCopyModel> extend
 
 					// Delegate to working copy model save method if any
 					if (typeof resolvedFileWorkingCopy.model.save === 'function') {
-						stat = await resolvedFileWorkingCopy.model.save(writeFileOptions, saveCancellation.token);
+						const result = await optionalIfCancelled((token) => resolvedFileWorkingCopy.model.save!(writeFileOptions, token), saveCancellation.token);
+						if (!result) {
+							return;
+						}
+						stat = result;
 					}
 
 					// Otherwise ask for a snapshot and save via file services