Function rustc_hir_analysis::check::check::check_opaque_meets_bounds

fn check_opaque_meets_bounds<'tcx>(
    tcx: TyCtxt<'tcx>,
    def_id: LocalDefId,
    substs: SubstsRef<'tcx>,
    span: Span,
    origin: &OpaqueTyOrigin
)

Check that the concrete type behind impl Trait actually implements Trait.

This is mostly checked at the places that specify the opaque type, but we check those cases in the param_env of that function, which may have bounds not on this opaque type:

type X = impl Clone fn f<T: Clone>(t: T) -> X { t }

Without this check the above code is incorrectly accepted: we would ICE if some tried, for example, to clone an Option<X<&mut ()>>.