trait Trait: Send: upcasting from dyn Trait to dyn Send does not work · Issue #126313 · rust-lang/rust (original) (raw)

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Description

The following compiles:

#![feature(trait_upcasting)] trait Super {} trait Trait: Super {} fn foo(x: &dyn Trait) -> &dyn Super { x }

while this does not:

#![feature(trait_upcasting)] trait Super {} trait Trait: Send {} fn foo(x: &dyn Trait) -> &dyn Send { x }

cc @compiler-errors I thought we actually had a PR for that at some point 🤔 I think that's actually not the case though. It wasn't part of #119338

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