`overwrite = false` should return contents of file

[kdheepak]

Currently overwrite = false creates a new file instead.

https://github.com/domluna/JuliaFormatter.jl/blob/9c2f82fb5a5a4699390b3c4dd42d35de3d325483/src/JuliaFormatter.jl#L344

It is possible that the user has a file in by that name in that location. I think overwrite = false should instead return the contents of the file.

This will make it easier to interface with vim plugins too.

[norru]

Or perhaps build a unique random temp file name?

[fleimgruber]

Or even change the behaviour so that it more closely resembles what gofmt and black do: If given the -d flag, they will print the diff of what would be done to stdout. Without the -d flag they will change the files in place.

Another thing I noticed in the help for --overwrite: https://github.com/domluna/JuliaFormatter.jl/blob/d1a2f0a95e923fb408bf39e126fe31a7d8d78928/bin/format.jl#L32

where for me this reads as saying that if --overwrite is true it will create a *_fmt file - but the implementation is actually the other way around as seen in OP code snippet.

[StefanKarpinski]

If overwrite = false is not going to write anything and just return the content of the formatted file, that should just be a completely separate function that does that.

[domluna]

I'm no longer convinced writing to a separate file is all that useful. In a realistic workflow you would just check the git diff. So I'm thinking of just removing the overwrite option.

Both gofmt and black shell out to diff -u (not sure about Windows) for the diff.

[fleimgruber]

AFAICS from a quick look black uses the difflib from stdlib for the actual diffing.

[SimonDanisch]

The overwrite=false option creating a new file seems pretty unusable ;)
I'd be in favor of it not doing anything, for lint checking without touching any files - that's how I thought I can use it, but can't because it still writes out new files...
Of course, in that case, it'd be nice to print any diffs :D

[penelopeysm]

I'm pretty sure it doesn't create a new file anymore, just returns the boolean indicating whether it's formatted or not.