pub(crate) fn cast_to_dyn_star<'tcx>(
    fx: &mut FunctionCx<'_, '_, 'tcx>,
    src: Value,
    src_ty_and_layout: TyAndLayout<'tcx>,
    dst_ty: Ty<'tcx>,
    old_info: Option<Value>,
) -> (Value, Value) {
    assert!(
        matches!(dst_ty.kind(), ty::Dynamic(_, _, ty::DynStar)),
        "destination type must be a dyn*"
    );
    (src, unsized_info(fx, src_ty_and_layout.ty, dst_ty, old_info))
}
Coerces `src` to `dst_ty` which is guaranteed to be a `dyn*` type.
src/unsize.rs