Reproducer: ```rs fn main() { trait Trait<'a, T> {} dbg!(std::any::type_name::<dyn Trait<'_, ()>>()); // yields `"dyn playground::main::Trait<, ()>"` // notice the "bad comma" } ``` Marked T-libs for obvious reasons but this is actually something that needs to be fixed in the compiler. Earlier Zulip discussion: [#t-compiler > `type_name` omits lifetimes?](https://rust-lang.zulipchat.com/#narrow/channel/131828-t-compiler/topic/.60type_name.60.20omits.20lifetimes.3F).