Check kernel dependencies when a new session is started (#16040)

* check dependencies when a new session is started

* fix test

* fix issue when kernel spec is not found

extensions/notebook/src/jupyter/jupyterServerInstallation.ts

@@ -476,7 +476,7 @@ export class JupyterServerInstallation implements IJupyterServerInstallation {
 
 							await fs.remove(this._oldPythonInstallationPath);
 							this._upgradeInProcess = false;
-						} else {
+						} else if (!installSettings.packageUpgradeOnly) {
 							await vscode.commands.executeCommand('notebook.action.restartJupyterNotebookSessions');
 						}
 					})

extensions/notebook/src/jupyter/jupyterSessionManager.ts

@@ -129,6 +129,12 @@ export class JupyterSessionManager implements nb.SessionManager {
 			// no-op
 			return Promise.reject(new Error(localize('errorStartBeforeReady', "Cannot start a session, the manager is not yet initialized")));
 		}
+
+		// Prompt for Python Install to check that all dependencies are installed.
+		// This prevents the kernel from getting stuck if a user deletes a dependency after the server has been started.
+		let kernelDisplayName: string = this.specs?.kernels.find(k => k.name === options.kernelName)?.display_name;
+		await this._installation?.promptForPythonInstall(kernelDisplayName);
+
 		let sessionImpl = await this._sessionManager.startNew(options);
 		let jupyterSession = new JupyterSession(sessionImpl, this._installation, skipSettingEnvironmentVars, this._installation?.pythonEnvVarPath);
 		await jupyterSession.messagesComplete;

extensions/notebook/src/test/model/sessionManager.test.ts

@@ -115,6 +115,7 @@ describe('Jupyter Session Manager', function (): void {
 			}
 		};
 		mockJupyterManager.setup(m => m.startNew(TypeMoq.It.isAny())).returns(() => Promise.resolve(expectedSessionInfo));
+		mockJupyterManager.setup(m => m.specs).returns(() => undefined);
 
 		// When I call startSession
 		let session = await sessionManager.startNew(sessionOptions, true);