async fn: 'static lifetime not inferred for Arc trait object

[inodentry]

Playground link to reproduce: https://play.rust-lang.org/?gist=697ecc0c55cbf30bee0fb2d87736f704&version=nightly&mode=debug&edition=2018

Changing the suggested type to Arc<SomeTrait + 'static> fixes the compiler error.

Having to manually specify this does not seem intentional. Perhaps this 'static lifetime should be automatically inferred?

[nikomatsakis]

Tagging as blocking -- this issue ought to be resolved before async-await can be stabilized, because it is generally surprising and kind of a bug. However, we expect it to get fixed by fixing #56238 (see that issue for notes as to why).