error: `C` is object-safe and has multiple supertraits --> $DIR/multiple_supertrait_upcastable.rs:7:1 | LL | trait C: A + B {} | ^^^^^^^^^^^^^^ | note: the lint level is defined here --> $DIR/multiple_supertrait_upcastable.rs:2:9 | LL | #![deny(multiple_supertrait_upcastable)] | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ error: aborting due to 1 previous error