--lineseparator option to use whatever separator the file is already using

[DetachHead]

in my team, some people use git core.autocrlf=true and others use input, which means robotidy will change the line endings unnecessarily. it would be nice if there was an option to make it use whatever line endings the file already has

[bhirsz]

Currently we have three (fixed) options: native, windows and linux. To implement your idea we would need to implement some sort of checker for separator type before running transformations (and we could call --lineseparator detect or --lineseparator keep). Is it what you have in mind?

What if line separator are not consistent? Easiest would be just use the first line separator. We could also try to count and pick most popular one (with small hit to performance but nothing noticeable).

[DetachHead]

i'm not sure what the best way is, maybe see how other formatters handle this issue? for example prettier: https://prettier.io/docs/en/options.html#end-of-line

"auto" - Maintain existing line endings (mixed values within one file are normalised by looking at what’s used after the first line)

[bhirsz]

"The other are doing this" is deciding factor ;) We can go with 'auto' and just check for first line ending. Basically if linesep is set to auto and we're saving the model to disk here:

robotframework-tidy/robotidy/app.py

Line 98 in d9a7cd6

ModelWriter(output=output, newline=self.formatting_config.line_sep).write(model)

then we could check the source for line endinds and use it instead. Here usage of 'newlines' attribute:
https://stackoverflow.com/questions/2798627/how-can-i-detect-dos-line-breaks-in-a-file

[bhirsz]

I can do it - or leave if for you if you want to create PR.

[DetachHead]

thanks! sorry i didn't see your comment