Slices and printfs

[zhiayang]

Currently the compiler automatically converts a str to its pointer when passing it to a C-style vararg function (eg. printf) (see

flax/source/codegen/call.cpp

Line 193 in 8402c46

// auto-convert strings and char slices into char* when passing to va_args

)

Of course this kinda defeats the purpose, since slices are not necessarily null-terminated. The proposed alternative (which I'm proposing now) is to pass the entire struct to printf, which will cause it to get both the length and the pointer.

(aside: the layout of str is like this: struct str { len: i64; ptr: &i8 })

Then, we would need to call printf with %.*s instead of just %s.

[zhiayang]

I lied, the layout of a slice currently is struct str { ptr: &i8; len: i64 } which needs to change.