Formatting replaces the entire file

[WhyNotHugo]

When formatting a file, ruff will replace the entire file with a formatted copy. It should only replace lines that have changed (as far as I can tell, this is what most LSPs do).

The issue with replacing the whole file, is that (at least on neovim) the cursor position is reset to the beginning of the file on background windows/splits, because the entire file was deleted/replaced.

Reproduction steps

• Open a well formatted file in neovim
• Open a split window (:vsp)
• Scroll on window to the middle of the file
• Switch to the unscrolled window
• Add an empty line at the beginning of the file
• Format the file using ruff-lsp

The cursor for the second split will now jump to the top of the file.

[WhyNotHugo]

I think that imara-diff can be used to actually calculate the regions that have changed:

https://docs.rs/imara-diff/0.1.5/imara_diff/sink/trait.Sink.html

[WhyNotHugo]

The format returned by imara-diff is also very close to the TextEdit format used in the LSP response:

https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#textEdit

Basically it is a matter of getting the ranges from the diff, and then serialising those as a TextEdit. Mostly a bit of glue code is needed here.

[WhyNotHugo]

Huh, looking at the source in _fixed_source_to_edits, is seems that the change is already narrowed down to a single TextEdit, which should avoid replacing the whole file in most cases.

I wonder if the root cause of the issue that I'm seeing is something else then.

[dhruvmanila]

Thanks for providing the reproduction steps!

I might be doing something wrong here but I'm unable to reproduce this in the way you've described in the "Reproduction steps" section. I've attached a screen recording of the same. Can you verify if that's what you intended on doing? I'm using the vim.lsp.buf.format() function to run the formatter through the ruff-lsp.

Screen.Recording.2024-02-12.at.11.55.52.mov

[MichaReiser]

@WhyNotHugo what LSP version are you using? I'm asking because the narrow edits feature has only been released with v0.0.52