Ensure we do not switch kernel if already the same

src/client/datascience/jupyter/kernels/kernel.ts

@@ -32,7 +32,7 @@ export class Kernel implements IKernel {
         if (this._notebook) {
             return this._notebook.getKernelSpec();
         }
-        return this._metadata.kernelSpec || this._metadata.kernelModel;
+        return this.metadata.kernelSpec || this.metadata.kernelModel;
     }
     get onStatusChanged(): Event<ServerStatus> {
         return this._onStatusChanged.event;
@@ -63,7 +63,7 @@ export class Kernel implements IKernel {
     private restarting?: Deferred<void>;
     constructor(
         public readonly uri: Uri,
-        private readonly _metadata: KernelSelection,
+        public readonly metadata: Readonly<KernelSelection>,
         private readonly notebookProvider: INotebookProvider,
         private readonly disposables: IDisposableRegistry,
         private readonly waitForIdleTimeoutMs: number,
@@ -93,8 +93,8 @@ export class Kernel implements IKernel {
             const metadata = ((getDefaultNotebookContent().metadata || {}) as unknown) as nbformat.INotebookMetadata;
             updateNotebookMetadata(
                 metadata,
-                this._metadata.interpreter,
-                this._metadata.kernelSpec || this._metadata.kernelModel
+                this.metadata.interpreter,
+                this.metadata.kernelSpec || this.metadata.kernelModel
             );
 
             this._notebookPromise = this.notebookProvider.getOrCreateNotebook({

src/client/datascience/jupyter/kernels/kernelProvider.ts

@@ -3,6 +3,7 @@
 
 'use strict';
 
+import * as fastDeepEqual from 'fast-deep-equal';
 import { inject, injectable } from 'inversify';
 import { Uri } from 'vscode';
 import { traceWarning } from '../../../common/logger';
@@ -25,10 +26,7 @@ export class KernelProvider {
     }
     public getOrCreate(uri: Uri, options: KernelOptions): IKernel | undefined {
         const existingKernelInfo = this.kernelsByUri.get(uri.toString());
-        if (
-            existingKernelInfo &&
-            JSON.stringify(existingKernelInfo.options.metadata) === JSON.stringify(options.metadata)
-        ) {
+        if (existingKernelInfo && fastDeepEqual(existingKernelInfo.options.metadata, options.metadata)) {
             return existingKernelInfo.kernel;
         }
 

src/client/datascience/jupyter/kernels/types.ts

@@ -57,6 +57,7 @@ export interface IKernelSelectionUsage {
 export interface IKernel extends IAsyncDisposable {
     readonly uri: Uri;
     readonly kernelSpec?: IJupyterKernelSpec | LiveKernelModel;
+    readonly metadata: Readonly<KernelSelection>;
     readonly onStatusChanged: Event<ServerStatus>;
     readonly onDisposed: Event<void>;
     readonly onRestarted: Event<void>;

src/client/datascience/notebook/helpers/executionHelpers.ts

@@ -5,6 +5,7 @@
 
 import type { nbformat } from '@jupyterlab/coreutils';
 import type { KernelMessage } from '@jupyterlab/services';
+import * as fastDeepEqual from 'fast-deep-equal';
 import { NotebookCell, NotebookCellRunState, NotebookDocument } from 'vscode';
 import { createErrorOutput } from '../../../../datascience-ui/common/cellFactory';
 import { createIOutputFromCellOutputs, createVSCCellOutputsFromOutputs, translateErrorOutput } from './helpers';
@@ -106,7 +107,7 @@ export function updateCellOutput(vscCell: NotebookCell, outputs: nbformat.IOutpu
     }
     // Compare outputs (at the end of the day everything is serializable).
     // Hence this is a safe comparison.
-    if (vscCell.outputs.length === newOutput.length && JSON.stringify(vscCell.outputs) === JSON.stringify(newOutput)) {
+    if (vscCell.outputs.length === newOutput.length && fastDeepEqual(vscCell.outputs, newOutput)) {
         return;
     }
     vscCell.outputs = newOutput;

src/client/datascience/notebook/kernelProvider.ts

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT License.
 
+import * as fastDeepEqual from 'fast-deep-equal';
 import { inject, injectable } from 'inversify';
 import { CancellationToken, Event, EventEmitter } from 'vscode';
 import {
@@ -13,6 +14,7 @@ import { IVSCodeNotebook } from '../../common/application/types';
 import { createPromiseFromCancellation } from '../../common/cancellation';
 import { IDisposableRegistry } from '../../common/types';
 import { noop } from '../../common/utils/misc';
+import { KernelProvider } from '../jupyter/kernels/kernelProvider';
 import { KernelSelectionProvider } from '../jupyter/kernels/kernelSelections';
 import { KernelSelector } from '../jupyter/kernels/kernelSelector';
 import { KernelSwitcher } from '../jupyter/kernels/kernelSwitcher';
@@ -22,6 +24,7 @@ import { INotebook, INotebookProvider } from '../types';
 import { getNotebookMetadata, isJupyterNotebook, updateKernelInNotebookMetadata } from './helpers/helpers';
 import { NotebookKernel } from './notebookKernel';
 import { INotebookContentProvider, INotebookExecutionService } from './types';
+
 @injectable()
 export class VSCodeKernelPickerProvider implements NotebookKernelProvider {
     public get onDidChangeKernels(): Event<void> {
@@ -33,6 +36,7 @@ export class VSCodeKernelPickerProvider implements NotebookKernelProvider {
         @inject(INotebookExecutionService) private readonly execution: INotebookExecutionService,
         @inject(KernelSelectionProvider) private readonly kernelSelectionProvider: KernelSelectionProvider,
         @inject(KernelSelector) private readonly kernelSelector: KernelSelector,
+        @inject(KernelProvider) private readonly kernelProvider: KernelProvider,
         @inject(IVSCodeNotebook) private readonly notebook: IVSCodeNotebook,
         @inject(INotebookStorageProvider) private readonly storageProvider: INotebookStorageProvider,
         @inject(INotebookProvider) private readonly notebookProvider: INotebookProvider,
@@ -87,14 +91,14 @@ export class VSCodeKernelPickerProvider implements NotebookKernelProvider {
             if (
                 preferredKernel.kernelSpec &&
                 item.kernelSpec &&
-                JSON.stringify(preferredKernel.kernelSpec) === JSON.stringify(item.kernelSpec)
+                fastDeepEqual(preferredKernel.kernelSpec, item.kernelSpec)
             ) {
                 return true;
             }
             if (
                 preferredKernel.kernelModel &&
                 item.kernelModel &&
-                JSON.stringify(preferredKernel.kernelModel) === JSON.stringify(item.kernelModel)
+                fastDeepEqual(preferredKernel.kernelModel, item.kernelModel)
             ) {
                 return true;
             }
@@ -130,12 +134,23 @@ export class VSCodeKernelPickerProvider implements NotebookKernelProvider {
             // Possibly closed or different kernel picked.
             return;
         }
+
         const model = await this.storageProvider.getOrCreateModel(document.uri);
         if (!model || !model.isTrusted) {
             // If a model is not trusted, we cannot change the kernel (this results in changes to notebook metadata).
             // This is because we store selected kernel in the notebook metadata.
             return;
         }
+
+        // Check what the existing kernel is.
+        const existingKernel = this.kernelProvider.get(document.uri);
+        if (existingKernel && fastDeepEqual(existingKernel.metadata, newKernelInfo.kernel.selection)) {
+            return;
+        }
+
+        // Make this the new kernel (calling this method will associate the new kernel with this Uri).
+        this.kernelProvider.getOrCreate(document.uri, { metadata: newKernelInfo.kernel.selection });
+
         // Change kernel and update metadata.
         const notebook = await this.notebookProvider.getOrCreateNotebook({
             resource: document.uri,

src/client/datascience/notebook/notebookKernel.ts

@@ -57,7 +57,7 @@ export class NotebookKernel implements VSCNotebookKernel {
     constructor(
         public readonly label: string,
         public readonly description: string,
-        private readonly selection: KernelSelection,
+        public readonly selection: Readonly<KernelSelection>,
         public readonly isPreferred: boolean,
         private readonly execution: INotebookExecutionService,
         private readonly kernelSelectionUsage: IKernelSelectionUsage