Extra newline added to cells after formatting with any formatter

Thanks so much for the native notebook experience: it’s awesome! One niggle that keeps biting me and my team: formatting cells (with autopep8, or yapf, or black) adds an empty line after each cell.

Steps to reproduce

• create a cell in a Jupyter notebook
• add any code in it, as long as it does not finish with a blank line
• format cell (e.g. with Shift+Alt+F)

Expected behaviour

• the number of lines in the cell stays unchanged, same as if you ran e.g. black on the notebook or autopep8 on the notebook.

Observed behaviour

• an empty new line is added at the end of the cell.

Cause

This is because VSCode formats cells by, quite cleverly, saving their content to a tempfile then running the formatter on that tempfile. All good formatters ensure the last line of the file finishes with a new line \n char: this is entirely expected for Python files, but not for notebook cells. Indeed adding such a newline at the end of the last line of a Jupyter notebook cell adds it to the cell’s JSON and is then interpreted as an actual new blank line displayed in the cell. In every single cell 😕 This is why for example black for notebooks removes that newline when called on notebooks and so do autopep8 callers on notebooks. See e.g. discussion in Black issue with @MarcoGorelli.

Suggested minimum fix

I think there’s a simple way to keep the common formatting-a-tempfile logic while still fixing this bug: modifying BaseFormatter.provideDocumentFormattingEdits() to, at line https://github.com/microsoft/vscode-python/blob/3698950c97982f31bb9dbfc19c4cd8308acda284/src/client/formatters/baseFormatter.ts#L78 or after applying the pach in https://github.com/microsoft/vscode-python/blob/3698950c97982f31bb9dbfc19c4cd8308acda284/src/client/formatters/baseFormatter.ts#L84 insert a promise that calls isNotebookCell(document) (like createTempFile does ) then if true removes the final newline.

I’m looking at making a PR to help, but never coded in TS, so filing this as an issue first.

Environment data

• VS Code version: 1.61.0
• Extension version (available under the Extensions sidebar): v2021.10.1317843341
• OS and version: Windows 10 20H2 with a WSL remote to an Ubuntu 20.04 (not that it matters for this bug 😃 )
• Python version (& distribution if applicable, e.g. Anaconda): All, but in this case 3.9.5 64bit
• Type of virtual environment used (N/A | venv | virtualenv | conda | …): conda with micromamba
• Relevant/affected Python packages and their versions: All
• Relevant/affected Python-related VS Code extensions and their versions: vscode-python
• Value of the python.languageServer setting: Default (with pylance installed)

[karthiknadig]

@jucor Can you try the black formatter extension we have? https://marketplace.visualstudio.com/items?itemName=ms-python.black-formatter

[hyiyang2022]

Any temporary fix?

@karthiknadig mentions to use the black formatter https://marketplace.visualstudio.com/items?itemName=ms-python.black-formatter, it works for me.