Tempalte Cell if the document is empty

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

@@ -199,6 +199,14 @@ export class MainThreadNotebookController implements IMainNotebookController {
 		let notebookHandle = await this._mainThreadNotebook.resolveNotebook(viewType, uri);
 		if (notebookHandle !== undefined) {
 			mainthreadNotebook = this._mapping.get(URI.from(uri).toString());
+			if (mainthreadNotebook && mainthreadNotebook.textModel.cells.length === 0) {
+				// it's empty, we should create an empty template one
+				const templateCell = await this._proxy.$createEmptyCell(this._viewType, uri, 0, mainthreadNotebook.textModel.languages.length ? mainthreadNotebook.textModel.languages[0] : '', CellKind.Code);
+				if (templateCell) {
+					let mainCell = new NotebookCellTextModel(URI.revive(templateCell.uri), templateCell.handle, templateCell.source, templateCell.language, templateCell.cellKind, templateCell.outputs, templateCell.metadata);
+					mainthreadNotebook.textModel.insertTemplateCell(mainCell);
+				}
+			}
 			return mainthreadNotebook?.textModel;
 		}
 

src/vs/workbench/contrib/notebook/browser/view/renderers/codeCell.ts

@@ -15,6 +15,7 @@ import { IQuickInputService, IQuickPickItem } from 'vs/platform/quickinput/commo
 import { INotebookService } from 'vs/workbench/contrib/notebook/browser/notebookService';
 import { CodeCellViewModel } from 'vs/workbench/contrib/notebook/browser/viewModel/codeCellViewModel';
 import { EDITOR_TOP_PADDING, EDITOR_BOTTOM_PADDING } from 'vs/workbench/contrib/notebook/browser/constants';
+import { IModeService } from 'vs/editor/common/services/modeService';
 
 interface IMimeTypeRenderer extends IQuickPickItem {
 	index: number;
@@ -28,7 +29,8 @@ export class CodeCell extends Disposable {
 		private viewCell: CodeCellViewModel,
 		private templateData: CellRenderTemplate,
 		@INotebookService private notebookService: INotebookService,
-		@IQuickInputService private readonly quickInputService: IQuickInputService
+		@IQuickInputService private readonly quickInputService: IQuickInputService,
+		@IModeService private readonly _modeService: IModeService
 	) {
 		super();
 
@@ -85,6 +87,11 @@ export class CodeCell extends Disposable {
 			templateData.editor?.updateOptions({ readOnly: !(viewCell.getEvaluatedMetadata(notebookEditor.viewModel?.metadata).editable) });
 		}));
 
+		this._register(viewCell.onDidChangeLanguage((e) => {
+			const mode = this._modeService.create(e);
+			templateData.editor?.getModel()?.setMode(mode.languageIdentifier);
+		}));
+
 		let cellWidthResizeObserver = getResizesObserver(templateData.editorContainer!, {
 			width: width,
 			height: totalHeight

src/vs/workbench/contrib/notebook/browser/viewModel/baseCellViewModel.ts

@@ -34,6 +34,8 @@ export abstract class BaseCellViewModel extends Disposable {
 	public readonly onDidChangeCursorSelection: Event<void> = this._onDidChangeCursorSelection.event;
 	protected readonly _onDidChangeMetadata: Emitter<NotebookCellMetadata | undefined> = this._register(new Emitter<NotebookCellMetadata | undefined>());
 	public readonly onDidChangeMetadata: Event<NotebookCellMetadata | undefined> = this._onDidChangeMetadata.event;
+	protected readonly _onDidChangeLanguage: Emitter<string> = this._register(new Emitter<string>());
+	public readonly onDidChangeLanguage: Event<string> = this._onDidChangeLanguage.event;
 	get handle() {
 		return this.cell.handle;
 	}
@@ -100,6 +102,10 @@ export abstract class BaseCellViewModel extends Disposable {
 	constructor(readonly viewType: string, readonly notebookHandle: number, readonly cell: ICell, public id: string) {
 		super();
 
+		this._register(cell.onDidChangeLanguage((e) => {
+			this._onDidChangeLanguage.fire(e);
+		}));
+
 		this._register(cell.onDidChangeMetadata((e) => {
 			this._onDidChangeMetadata.fire(e);
 		}));

src/vs/workbench/contrib/notebook/browser/viewModel/codeCellViewModel.ts

@@ -89,6 +89,12 @@ export class CodeCellViewModel extends BaseCellViewModel implements ICellViewMod
 				this.layoutChange({ outerWidth: e.value.width, font: e.value.fontInfo });
 			}
 		}));
+
+		this._register(this.onDidChangeLanguage((e) => {
+			if (this._textModel && !this._textModel.isDisposed()) {
+
+			}
+		}));
 	}
 
 	layoutChange(state: CodeCellLayoutChangeEvent) {

src/vs/workbench/contrib/notebook/common/model/notebookCellTextModel.ts

@@ -18,6 +18,9 @@ export class NotebookCellTextModel implements ICell {
 	private _onDidChangeMetadata = new Emitter<NotebookCellMetadata | undefined>();
 	onDidChangeMetadata: Event<NotebookCellMetadata | undefined> = this._onDidChangeMetadata.event;
 
+	private _onDidChangeLanguage = new Emitter<string>();
+	onDidChangeLanguage: Event<string> = this._onDidChangeLanguage.event;
+
 	private _outputs: IOutput[];
 
 	get outputs(): IOutput[] {
@@ -44,13 +47,22 @@ export class NotebookCellTextModel implements ICell {
 		this._onDidChangeMetadata.fire(this._metadata);
 	}
 
+	get language() {
+		return this._language;
+	}
+
+	set language(newLanguage: string) {
+		this._language = newLanguage;
+		this._onDidChangeLanguage.fire(newLanguage);
+	}
+
 	private _buffer: PieceTreeTextBufferFactory | null = null;
 
 	constructor(
 		readonly uri: URI,
 		public handle: number,
 		private _source: string[],
-		public language: string,
+		private _language: string,
 		public cellKind: CellKind,
 		outputs: IOutput[],
 		metadata: NotebookCellMetadata | undefined

src/vs/workbench/contrib/notebook/common/model/notebookTextModel.ts

@@ -24,6 +24,7 @@ export class NotebookTextModel extends Disposable implements INotebookTextModel
 	languages: string[] = [];
 	metadata: NotebookDocumentMetadata | undefined = { editable: true };
 	renderers = new Set<number>();
+	private _isUntitled: boolean | undefined = undefined;
 
 	constructor(
 		public handle: number,
@@ -36,6 +37,11 @@ export class NotebookTextModel extends Disposable implements INotebookTextModel
 
 	updateLanguages(languages: string[]) {
 		this.languages = languages;
+
+		// TODO@rebornix metadata: default language for cell
+		if (this._isUntitled && languages.length && this.cells.length) {
+			this.cells[0].language = languages[0];
+		}
 	}
 
 	updateNotebookMetadata(metadata: NotebookDocumentMetadata) {
@@ -57,7 +63,27 @@ export class NotebookTextModel extends Disposable implements INotebookTextModel
 		});
 	}
 
+	insertTemplateCell(cell: NotebookCellTextModel) {
+		if (this.cells.length > 0 || this._isUntitled !== undefined) {
+			return;
+		}
+
+		this._isUntitled = true;
+		this.cells = [cell];
+
+		let dirtyStateListener = cell.onDidChangeContent(() => {
+			this._isUntitled = false;
+			this._onDidChangeContent.fire();
+		});
+
+		this._cellListeners.set(cell.handle, dirtyStateListener);
+		this._onDidChangeContent.fire();
+		return;
+	}
+
 	insertNewCell(index: number, cell: NotebookCellTextModel): void {
+		this._isUntitled = false;
+
 		this._mapping.set(cell.handle, cell);
 		this.cells.splice(index, 0, cell);
 		let dirtyStateListener = cell.onDidChangeContent(() => {
@@ -70,6 +96,8 @@ export class NotebookTextModel extends Disposable implements INotebookTextModel
 	}
 
 	removeCell(index: number) {
+		this._isUntitled = false;
+
 		let cell = this.cells[index];
 		this._cellListeners.get(cell.handle)?.dispose();
 		this._cellListeners.delete(cell.handle);
@@ -80,6 +108,12 @@ export class NotebookTextModel extends Disposable implements INotebookTextModel
 
 	// TODO@rebornix should this trigger content change event?
 	$spliceNotebookCells(splices: NotebookCellsSplice[]): void {
+		if (!splices.length) {
+			return;
+		}
+
+		this._isUntitled = false;
+
 		splices.reverse().forEach(splice => {
 			let cellDtos = splice[2];
 			let newCells = cellDtos.map(cell => {

src/vs/workbench/contrib/notebook/common/notebookCommon.ts

@@ -136,6 +136,7 @@ export interface ICell {
 	metadata?: NotebookCellMetadata;
 	onDidChangeOutputs?: Event<NotebookCellOutputsSplice[]>;
 	onDidChangeMetadata: Event<NotebookCellMetadata | undefined>;
+	onDidChangeLanguage: Event<string>;
 	resolveTextBufferFactory(): PieceTreeTextBufferFactory;
 	// TODO@rebornix it should be later on replaced by moving textmodel resolution into CellTextModel
 	contentChange(): void;

src/vs/workbench/contrib/notebook/test/testNotebookEditor.ts

@@ -27,6 +27,9 @@ export class TestCell implements ICell {
 	onDidChangeOutputs: Event<NotebookCellOutputsSplice[]> = this._onDidChangeOutputs.event;
 	private _onDidChangeMetadata = new Emitter<NotebookCellMetadata>();
 	onDidChangeMetadata: Event<NotebookCellMetadata> = this._onDidChangeMetadata.event;
+	private _onDidChangeLanguage = new Emitter<string>();
+	onDidChangeLanguage: Event<string> = this._onDidChangeLanguage.event;
+
 	private _isDirty: boolean = false;
 	private _outputs: IOutput[];