Clarify unsafety

[konsumlamm]

unsafeEncodeUtf only throws a (pure) exception on invalid input. This is not unsafe in the same way as e.g. unsafePerformIO, which can cause undefined behaviour. Other functions that also throw pure exceptions (like head) are documented as partial (which is more correct in my opinion).

unsafeFromChar only truncates its input. In what way is this unsafe? Can it cause undefined behaviour?

I think the documentation for these functions should be clarified.

[hasufell]

I don't think there's a clear consensus about what "safe"/"unsafe" means.

If you loook at Safe then it uses the "(un)safe" terminology for things that may crash.

My motivation to name these unsafe is because Data.ByteString.Char8 has been a common source of confusion and bugs, although it's perfectly memory safe and doesn't exhibit undefined behavior. These functions are also (mostly) not partial (truncation is neither partial, nor unsafe in that sense).

But I want to make very clear that you're essentially leaving the guaranteed invariants of the library when you're using these functions. That is what "unsafe" means here: use at your own risk.