Code change:
<ins> /*--------------------------------------------------------------------------------------------- *  Copyright (c) Microsoft Corporation. All rights reserved. *  Licensed under the MIT License. See License.txt in the project root for license information. *--------------------------------------------------------------------------------------------*/ import { ExtensionContext, NotebookCellKind, NotebookDocument, NotebookDocumentChangeEvent, NotebookEdit, workspace, WorkspaceEdit, type NotebookCell, type NotebookDocumentWillSaveEvent } from 'vscode'; import { getCellMetadata, getVSCodeCellLanguageId, removeVSCodeCellLanguageId, setVSCodeCellLanguageId } from './serializers'; import { CellMetadata } from './common'; import { getNotebookMetadata } from './notebookSerializer'; import type * as nbformat from '@jupyterlab/nbformat'; const noop = () => { // }; /** * Code here is used to ensure the Notebook Model is in sync the the ipynb JSON file. * E.g. assume you add a new cell, this new cell will not have any metadata at all. * However when we save the ipynb, the metadata will be an empty object `{}`. * Now thats completely different from the metadata os being `empty/undefined` in the model. * As a result, when looking at things like diff view or accessing metadata, we'll see differences. * * This code ensures that the model is in sync with the ipynb file. */ export const pendingNotebookCellModelUpdates = new WeakMap<NotebookDocument, Set<Thenable<void>>>(); export function activate(context: ExtensionContext) { workspace.onDidChangeNotebookDocument(onDidChangeNotebookCells, undefined, context.subscriptions); workspace.onWillSaveNotebookDocument(waitForPendingModelUpdates, undefined, context.subscriptions); } function isSupportedNotebook(notebook: NotebookDocument) { return notebook.notebookType === 'jupyter-notebook' || notebook.notebookType === 'interactive'; } function waitForPendingModelUpdates(e: NotebookDocumentWillSaveEvent) { if (!isSupportedNotebook(e.notebook)) { return; } const promises = pendingNotebookCellModelUpdates.get(e.notebook); if (!promises) { return; } e.waitUntil(Promise.all(promises)); } function cleanup(notebook: NotebookDocument, promise: PromiseLike<void>) { const pendingUpdates = pendingNotebookCellModelUpdates.get(notebook); if (pendingUpdates) { pendingUpdates.delete(promise); if (!pendingUpdates.size) { pendingNotebookCellModelUpdates.delete(notebook); } } } function trackAndUpdateCellMetadata(notebook: NotebookDocument, cell: NotebookCell, metadata: CellMetadata & { vscode?: { languageId: string } }) { const pendingUpdates = pendingNotebookCellModelUpdates.get(notebook) ?? new Set<Thenable<void>>(); pendingNotebookCellModelUpdates.set(notebook, pendingUpdates); const edit = new WorkspaceEdit(); edit.set(cell.notebook.uri, [NotebookEdit.updateCellMetadata(cell.index, { ...(cell.metadata), custom: metadata })]); const promise = workspace.applyEdit(edit).then(noop, noop); pendingUpdates.add(promise); const clean = () => cleanup(notebook, promise); promise.then(clean, clean); } function onDidChangeNotebookCells(e: NotebookDocumentChangeEvent) { if (!isSupportedNotebook(e.notebook)) { return; } const notebook = e.notebook; const notebookMetadata = getNotebookMetadata(e.notebook); // use the preferred language from document metadata or the first cell language as the notebook preferred cell language const preferredCellLanguage = notebookMetadata.metadata?.language_info?.name; // When we change the language of a cell, // Ensure the metadata in the notebook cell has been updated as well, // Else model will be out of sync with ipynb https://github.com/microsoft/vscode/issues/207968#issuecomment-2002858596 e.cellChanges.forEach(e => { if (!preferredCellLanguage || e.cell.kind !== NotebookCellKind.Code) { return; } const languageIdInMetadata = getVSCodeCellLanguageId(getCellMetadata(e.cell)); if (e.cell.document.languageId !== preferredCellLanguage && e.cell.document.languageId !== languageIdInMetadata) { const metadata: CellMetadata = JSON.parse(JSON.stringify(getCellMetadata(e.cell))); metadata.metadata = metadata.metadata || {}; setVSCodeCellLanguageId(metadata, e.cell.document.languageId); trackAndUpdateCellMetadata(notebook, e.cell, metadata); } else if (e.cell.document.languageId === preferredCellLanguage && languageIdInMetadata) { const metadata: CellMetadata = JSON.parse(JSON.stringify(getCellMetadata(e.cell))); metadata.metadata = metadata.metadata || {}; removeVSCodeCellLanguageId(metadata); trackAndUpdateCellMetadata(notebook, e.cell, metadata); } else if (e.cell.document.languageId === preferredCellLanguage && e.cell.document.languageId === languageIdInMetadata) { const metadata: CellMetadata = JSON.parse(JSON.stringify(getCellMetadata(e.cell))); metadata.metadata = metadata.metadata || {}; removeVSCodeCellLanguageId(metadata); trackAndUpdateCellMetadata(notebook, e.cell, metadata); } }); // Ensure all new cells in notebooks with nbformat >= 4.5 have an id. // Details of the spec can be found here https://jupyter.org/enhancement-proposals/62-cell-id/cell-id.html# e.contentChanges.forEach(change => { change.addedCells.forEach(cell => { // When ever a cell is added, always update the metadata // as metadata is always an empty `{}` in ipynb JSON file const cellMetadata = getCellMetadata(cell); // Avoid updating the metadata if it's not required. if (cellMetadata.metadata) { if (!isCellIdRequired(notebookMetadata)) { return; } if (isCellIdRequired(notebookMetadata) && cellMetadata?.id) { return; } } // Don't edit the metadata directly, always get a clone (prevents accidental singletons and directly editing the objects). const metadata: CellMetadata = { ...JSON.parse(JSON.stringify(cellMetadata || {})) }; metadata.metadata = metadata.metadata || {}; if (isCellIdRequired(notebookMetadata) && !cellMetadata?.id) { metadata.id = generateCellId(e.notebook); } trackAndUpdateCellMetadata(notebook, cell, metadata); }); }); } /** * Cell ids are required in notebooks only in notebooks with nbformat >= 4.5 */ function isCellIdRequired(metadata: Pick<Partial<nbformat.INotebookContent>, 'nbformat' | 'nbformat_minor'>) { if ((metadata.nbformat || 0) >= 5) { return true; } if ((metadata.nbformat || 0) === 4 && (metadata.nbformat_minor || 0) >= 5) { return true; } return false; } function generateCellId(notebook: NotebookDocument) { while (true) { // Details of the id can be found here https://jupyter.org/enhancement-proposals/62-cell-id/cell-id.html#adding-an-id-field, // & here https://jupyter.org/enhancement-proposals/62-cell-id/cell-id.html#updating-older-formats const id = generateUuid().replace(/-/g, '').substring(0, 8); let duplicate = false; for (let index = 0; index < notebook.cellCount; index++) { const cell = notebook.cellAt(index); const existingId = getCellMetadata(cell)?.id; if (!existingId) { continue; } if (existingId === id) { duplicate = true; break; } } if (!duplicate) { return id; } } } /** * Copied from src/vs/base/common/uuid.ts */ function generateUuid() { // use `randomValues` if possible function getRandomValues(bucket: Uint8Array): Uint8Array { for (let i = 0; i < bucket.length; i++) { bucket[i] = Math.floor(Math.random() * 256); } return bucket; } // prep-work const _data = new Uint8Array(16); const _hex: string[] = []; for (let i = 0; i < 256; i++) { _hex.push(i.toString(16).padStart(2, '0')); } // get data getRandomValues(_data); // set version bits _data[6] = (_data[6] & 0x0f) | 0x40; _data[8] = (_data[8] & 0x3f) | 0x80; // print as string let i = 0; let result = ''; result += _hex[_data[i++]]; result += _hex[_data[i++]]; result += _hex[_data[i++]]; result += _hex[_data[i++]]; result += '-'; result += _hex[_data[i++]]; result += _hex[_data[i++]]; result += '-'; result += _hex[_data[i++]]; result += _hex[_data[i++]]; result += '-'; result += _hex[_data[i++]]; result += _hex[_data[i++]]; result += '-'; result += _hex[_data[i++]]; result += _hex[_data[i++]]; result += _hex[_data[i++]]; result += _hex[_data[i++]]; result += _hex[_data[i++]]; result += _hex[_data[i++]]; return result; } </ins>

Related discussion:
text: <details<summaryInternal Notes</summaryHere's the work flow Add a cell A change event is triggered, undo redo stack is updated Last undo redo is User hits save button Working copy starts to handle the save operation Save participants start We add a save participant and update the model via a work space edit Now a new change event is triggered This results in a whole new undo redo stack The latest (last) undo redo item is Save participants done Working copy keeps track of the last as the entry for Problems Time line does not include , time line shows only I guess this is correct, However from a users perspective, the labels are never going to be meaningful as we'd always say . </details