Extra newline added to cells after formatting with any formatter

[jucor]

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

vscode-python/src/client/formatters/baseFormatter.ts

Line 78 in 3698950

.then((output) => output.stdout)

or after applying the pach in

vscode-python/src/client/formatters/baseFormatter.ts

Line 84 in 3698950

})

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)

[jucor]

Tagging @DonJayamanne who kindly authored the support for formatting notebooks in #12199, and @rchiodo and @IanMatthewHuff who reviewed so might be familiar with the topic. Thanks for your attention and your time :)

[karthiknadig]

@jucor Thanks for investigating this issue. We have marked this as needs PR, so it is ready to be worked on. We are happy to review any PR fixing this issue.

[karthiknadig]

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

[alex180500]

Any temporary fix?

[ghost]

Any temporary fix?

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

[gsnidero]

works for me too!
VSC Version: 1.73.1 (Universal)
jupyter: v2022.9.1202862440
black formatter: v2022.6.0

[karthiknadig]

Thank for try the black formatter extension. Going forward that will be the way we provide formatting feature. We have started the process of migrating users over from current experience to the new extensions.