use compilation buffer for rustfmt errors

[brotzeit]

No description provided.

[tromey]

I like this idea, but I wonder about removing the "exit code 3" handling. IIRC that is there because sometimes rustfmt can't format specific lines -- so currently the changes are applied and a warning is given, but with this change, the changes won't be applied.

[brotzeit]

I forgot about that problem. That was actually the reason I closed a previous PR.
The updated solution is not very pretty but I haven't seen any other error with exit code 3 than "line exceeded maximum width".

I will use this solution, but I have no problem with changing it again if anybody has a better idea. But IMO this is much more convenient.

[tromey]

Do you know why this code previously used a temporary file? I wonder if there was some issue with using stdin.

[tromey]

I don't understand what this loop is for. Could you add a comment explaining it?

[brotzeit]

This removes the actual file contents from the compilation buffer, but you're right that can be done better. IMO rustfmt shouldn't format files if there are any kind of errors. I mean I have to take care of them anyway as I don't want an error message every time I use rustfmt. Hopefully that will be changed when it's more mature.

I can understand if you don't want to merge it, as it won't work correctly in every situation. I can try to make this more sound, but I can also wait until there's an improvement on the rustfmt side and give it another try.

[nikomatsakis]

I know nothing, but I'm curious why we can't use compilation-start?

[brotzeit]

I think compilation-start doesn't allow piping through stdin.