Diagnostic customization

[Niki4tap]

Rustc has a good API for this that clippy uses: https://doc.rust-lang.org/stable/nightly-rustc/rustc_errors/struct.DiagnosticBuilder.html

Marker should probably have something like this too :)

[xFrednet]

Agreed, related to: #47

We should be careful, to decide which API we want to provide since we'll require all backends to support that. On the other hand there is currently only rustc and RA which support the same things

[Niki4tap]

Oh, hmm, the issue you linked seems nearly identical, somehow overlooked it, should I close this in favor of #47?

[xFrednet]

Yeah, I'll copy my comment over to that one :)