Implement formatting using Language Server Protocol

[karthiknadig]

Implement following formatters using LSP:

• black
• autopep8
• yapf

[memeplex]

#18121 was closed in favor of this. Ok, but I'm not sure that moving formatting to LSP will automatically work without quirks inside notebook cells. For example, black works at the file level, some criteria that is sensible at that level isn't at the cell level. I reckon that Jupyter Lab extensions that do black formatting use specific heuristics to deal with these issues.

[breathe]

Any update on this -- trying to decide if its worth it to file a bug about the existing formatting behaviors ...

For example -- it doesn't seem to be possible to force the yapf extension to use one specific yapf implementation for a python mono-repo ... The extension won't expand variables in the path arguments provided to yapf and will always choose the python environment associated with the file as the root path from which to search for python ... This forces you to install yapf in every virtual env within a monorepo -- which is highly undesirable.

With below for example: trying to point the extension at the yapf installed in the venv associated with the 'iac' workspace:

  "python.formatting.provider": "yapf",
  "python.formatting.yapfArgs": [
    "--style",
    "${workspaceFolder:iac}/.style.yapf"
  ],
  "python.formatting.yapfPath": "${workspaceFolder:iac}/.venv/bin/yapf"

Error: spawn /path/to/some/python/workspace/${workspaceFolder:iac}/blah/.venv/bin/yapf ENOENT

[karthiknadig]

${workspaceFolder:iac} this type of expansion is not support. Actually VS Code itself does not support expanding variables in settings. This was something that python extension added. We do expand it but in limited scenarios, so ${workspaceFolder} should work for now, but ${workspaceFolder:iac} won't.

I am currently working on this for this milestone.

[karthiknadig]

Black formatter (pre-release) now available here: https://marketplace.visualstudio.com/items?itemName=ms-python.black-formatter