using black as formatter will need two runs on four+ newlines

[hochreitercorpuls]

Environment data

• VS Code version: 1.43.2
• Extension version (available under the Extensions sidebar): 2020.3.71659
• OS and version: Windows 10 18363.752
• Python version (& distribution if applicable, e.g. Anaconda): 3.7.7 (Anaconda)
• Type of virtual environment used (N/A | venv | virtualenv | conda | ...): conda
• Relevant/affected Python packages and their versions: black 19.10b0
• Jedi or Language Server? (i.e. what is "python.jediEnabled" set to; more info How to update the language server to the latest stable version #3977): disabled
• Black arguments: "python.formatting.blackArgs": []

Expected behaviour

given a python file like this (with 4+ lines between import statements and the first function definition):

import numpy as np




def test():
    return 0

I'd expect running black inside VS Code to reformat the given file would lead to a file like this:

import numpy as np


def test():
    return 0

with two newlines after the import statements. Running black link_to_file.py manually in a conda shell does exactly what is expected.

Actual behaviour

Actually a first run of black leads to three newlines inbetween imports and first definition

import numpy as np



def test():
    return 0

and a second run is needed to get to the expectet result.

Steps to reproduce:

see above

[karthiknadig]

The issue seems to be with this line where we parse diffs:
https://github.com/Microsoft/vscode-python/blob/61b179b2092050709e3c373a6738abad8ce581c4/src/client/common/editor.ts#L74-L79

We should likely get rid of the diff-match-patch and generate the edits directly. somewhere between extracting the patches and re-applying line ending we are adding additional line endings.

[hochreitercorpuls]

Now with VS Code Python 2020.10.332... also the second black run fails - leaving the file with two lines between imports and function definition.

import numpy as np


def test():
    return 0

sorry for the confusion - @ichard26 is absolutely right - i got confused about what was exepcted and what wasn't

yet the other issues remain.

[ichard26]

@hochreitercorpuls that is expected behaviour as top level functions (and classes too) are always surrounded by two empty lines (unless it's at the start or the end of the file) by Black.

[TBBle]

I've just found that the VSCode-black integration is not adding a newline to the end of a file that does not have one.

I suspect this is the same problem as this, based on other similar problems being duplicated to this issue.

Manually adding the missing line is not removed when saving, suggesting that it's the same issue as this.

With the same binary, black --check rejects such a file (as does my CI pipeline, thankfully), and manually running black without --diff (as used by VSCode) does add the missing newline.

As a workaround for this, I can set Python files to always insert the final newline in my setings.json.

  "[python]": {
    "files.insertFinalNewline": true
  },

although I'm not currently having problems with excess final newlines being removed, I assume setting files.trimFinalNewlines similarly would work around that form of this problem.

As a quick sanity check, I confirmed that the problem happens in both LF and CRLF file modes.

[ichard26]

@TBBle it's an issue on Black's side not VS Code's -> psf/black#1662

[TBBle]

Ah, thank you. Sorry for the noise.

[karthiknadig]

This should be working better with the formatter extension, please try that.
https://marketplace.visualstudio.com/items?itemName=ms-python.black-formatter

This feature is moved to the extension, and future features and bugs will be addressed there: https://github.com/microsoft/vscode-black-formatter