Unsaved notebook fails to render when a folder is added to the workspace

[minsa110]

Does this issue occur when all extensions are disabled?: Yes/No

Version: 1.75.0-insider (user setup)
Commit: e2816fe
Date: 2023-02-01T15:16:18.248Z
Electron: 19.1.9
Chromium: 102.0.5005.194
Node.js: 16.14.2
V8: 10.2.154.23-electron.0
OS: Windows_NT x64 10.0.22621
Sandboxed: Yes

Steps to Reproduce:

1. Open a folder
2. Make changes to an ipynb file but don't save
3. Add a folder to the workspace
4. Click "Cancel" when prompted to save
5. The ipynb file doesn't render in notebook view (I could open it as json if I click "Open in Text Editor" though)
6. Workaround is to reload the window

[bpasero]

The underlying reason is very likely the fact that we restart the extension host which is tough for any editor that requires the EH to work (for example custom editors).

Here the stack trace is:

notebookEditor.js:194 TypeError: Cannot read properties of undefined (reading 'onDidChangeContent')
    at NotebookEditor.setInput (notebookEditor.js:154:64)
    at async EditorPanes.doSetInput (editorPanes.js:292:17)
    at async EditorPanes.doOpenEditor (editorPanes.js:166:44)
    at async EditorPanes.openEditor (editorPanes.js:65:24)
    at async editorGroupView.js:809:65

I suspect some disposal code running from notebooks clearing out the model.

[roblourens]

I guess

1. Why is it forcing a save?
2. And if I cancel the save, why doesn't that cancel reloading the EH?

[bpasero]

@roblourens because all notebooks get disposed:

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

Lines 41 to 44 in 43db9d2

	dispose(): void {
	this._disposables.dispose();
	dispose(this._notebookSerializer.values());
	}

Which triggers closing:

vscode/src/vs/workbench/contrib/notebook/browser/notebook.contribution.ts

Lines 562 to 568 in 43db9d2

	// CLOSE notebook editor for models that have no more serializer
	this._disposables.add(notebookService.onWillRemoveViewType(e => {
	for (const group of editorGroups.groups) {
	const staleInputs = group.editors.filter(input => input instanceof NotebookEditorInput && input.viewType === e);
	group.closeEditors(staleInputs);
	}
	}));

We cannot cancel restart of the EH today through any user interaction and to be fair, restarting the EH is somewhat silly still and just to support deprecated API for the root path...

[roblourens]

Yeah, I just would have to read more to follow how this is different than closing vscode where hot exit works. But true, we still have the huge thread at #69335 and I think that getting rid of restarting the EH is the right fix for this situation.