Change cell language fires change event

[DonJayamanne]

Version: 1.46.0-insider

• Commit: cd41dd1
• Date: 2020-05-29T05:45:24.735Z
• Electron: 7.3.0
• Chrome: 78.0.3904.130
• Node.js: 12.8.1
• V8: 7.8.279.23-electron.0
• OS: Darwin x64 19.5.0

Steps to Reproduce:

1.Open a notebook
2.Create a markdown cell and change the language to markdown.

A notebook event if fires for change of cell language even though the current language is already the same.

I would not expect the event to get fired if the cell language is the same.
Also as a side effect the cell output change event also gets fired (feels this is a noop change, hence events shouldn't get fired)

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

@rebornix

[vscodebot]

(Experimental duplicate detection)
Thanks for submitting this issue. Please also check if it is already covered by an existing one, like:

• API - Event that fires when a file is opened (#66143)

[RMacfarlane]

I'm trying to use a vscode.notebook.onDidChangeCellLanguage listener, but this seems to never be called now, even if I do change a cell to a different language.

vscode.notebook.onDidChangeNotebookCells does get fired when the language is changed.

[rebornix]

@RMacfarlane did you switch only between Markdown and GitHub Issue Notebook, if so it's expected as switching between markdown and code cells is a cellsChange event but not a language change event.

[RMacfarlane]

Ah, yes, that is what I did. How do I change to a language outside of those?

[rebornix]

@RMacfarlane you can try

• Firstly clone https://github.com/microsoft/vscode-notebook-renderer-starter
• Add multiple language support to sample provider https://github.com/microsoft/vscode-notebook-renderer-starter/blob/master/src/extension/sampleProvider.ts#L49 . Change languages to ['json', 'css']
• Register a cell language listener in https://github.com/microsoft/vscode-notebook-renderer-starter/blob/master/src/extension/extension.ts#L24
• F5
• Create a *.sample file and open
• Switch language from json to css

[RMacfarlane]

Thanks, that worked!