tests/ui/wf/wf-packed-on-proj-of-type-as-unimpl-trait.rs

   1 // rust-lang/rust#58158: We have special-case code to deal with case
   2 // when a type is both packed and needs drop glue, (we move the fields
   3 // out of their potentially unaligned locations before dropping them,
   4 // which requires they be Sized; see PR #44884).
   5 //
   6 // So, we need to check if a given type needs drop-glue. That requires
   7 // that we actually know that the concrete type, and we guard against
   8 // the type having unknown parts (i.e. type variables) by ICE'ing in
   9 // that scenario.
  10 //
  11 // But in a case where we have a projection (`Type as Trait::Assoc`)
  12 // where `Type` does not actually implement `Trait`, we of course
  13 // cannot have a concrete type, because there is no impl to look up
  14 // the concrete type for the associated type `Assoc`.
  15 //
  16 // So, this test is just making sure that in such a case that we do
  17 // not immediately ICE, and instead allow the underlying type error to
  18 // surface.
  19
  20 pub struct Matrix<S>(S);
  21 pub struct DefaultAllocator;
  22
  23 pub trait Allocator { type Buffer; }
  24
  25 // impl Allocator for DefaultAllocator { type Buffer = (); }
  26
  27 #[repr(packed)]
  28 struct Foo(Matrix<<DefaultAllocator as Allocator>::Buffer>);
  29 //~^ ERROR the trait bound `DefaultAllocator: Allocator` is not satisfied
  30
  31 fn main() { }