Intrinsic for type_name_of_id to power a better impl Debug for TypeId? · Issue #61533 · rust-lang/rust (original) (raw)

Currently TypeIds have uninformative derived Debug impls:

fn main() { println!("{:?}", std::any::TypeId::of::()); }

   Compiling playground v0.0.1 (/playground)
    Finished dev [unoptimized + debuginfo] target(s) in 0.91s
     Running `target/debug/playground`
TypeId { t: 8766594652559642870 }

This results in fairly poor Debug output for dynamic types like anymap.

I think it could be quite nice for debugging/logging/etc to allow printing the type name from a TypeId in the Debug impl. It would provide an out of the box improvement to debugging existing dynamic typing tools, and IIUC the contents of Debug impls in the standard library are not considered stable so there's neither a breaking change here nor a de facto stabilization of the type_name representation.

I assume this would need to rely on some unstable intrinsic being exposed to get the type_name of an ID at run time, but I'm not really aware what would be needed.

Thoughts? cc @oli-obk as we had discussed this a bit on IRC.