error[E0700]: hidden type for `Opaque(DefId(0:13 ~ impl_trait_captures[aeb9]::foo::{opaque#0}), [ReEarlyBound(0, 'a), T, ReEarlyBound(0, 'a)])` captures lifetime that does not appear in bounds --> $DIR/impl-trait-captures.rs:11:5 | LL | fn foo<'a, T>(x: &T) -> impl Foo<'a> { | -- ------------ opaque type defined here | | | hidden type `&ReFree(DefId(0:8 ~ impl_trait_captures[aeb9]::foo), BrNamed(DefId(0:12 ~ impl_trait_captures[aeb9]::foo::'_), '_)) T` captures the anonymous lifetime defined here LL | x | ^ | help: to declare that `Opaque(DefId(0:13 ~ impl_trait_captures[aeb9]::foo::{opaque#0}), [ReEarlyBound(0, 'a), T, ReEarlyBound(2, 'a)])` captures `ReFree(DefId(0:8 ~ impl_trait_captures[aeb9]::foo), BrNamed(DefId(0:12 ~ impl_trait_captures[aeb9]::foo::'_), '_))`, you can add an explicit `ReFree(DefId(0:8 ~ impl_trait_captures[aeb9]::foo), BrNamed(DefId(0:12 ~ impl_trait_captures[aeb9]::foo::'_), '_))` lifetime bound | LL | fn foo<'a, T>(x: &T) -> impl Foo<'a> + ReFree(DefId(0:8 ~ impl_trait_captures[aeb9]::foo), BrNamed(DefId(0:12 ~ impl_trait_captures[aeb9]::foo::'_), '_)) { | ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ error: aborting due to previous error For more information about this error, try `rustc --explain E0700`.