diff options
4 files changed, 60 insertions, 5 deletions
diff --git a/compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs b/compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs index 6045001510e..69af33e874b 100644 --- a/compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs +++ b/compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs @@ -100,10 +100,18 @@ impl<'tcx> InferCtxtSelectExt<'tcx> for InferCtxt<'tcx> { rematch_impl(self, goal, def_id, nested_obligations) } + // If an unsize goal is ambiguous, then we can manually rematch it to make + // selection progress for coercion during HIR typeck. If it is *not* ambiguous, + // but is `BuiltinImplSource::Misc`, it may have nested `Unsize` goals, + // and we need to rematch those to detect tuple unsizing and trait upcasting. + // FIXME: This will be wrong if we have param-env or where-clause bounds + // with the unsize goal -- we may need to mark those with different impl + // sources. (Certainty::Maybe(_), CandidateSource::BuiltinImpl(src)) + | (Certainty::Yes, CandidateSource::BuiltinImpl(src @ BuiltinImplSource::Misc)) if self.tcx.lang_items().unsize_trait() == Some(goal.predicate.def_id()) => { - rematch_unsize(self, goal, nested_obligations, src) + rematch_unsize(self, goal, nested_obligations, src, certainty) } // Technically some builtin impls have nested obligations, but if @@ -217,6 +225,7 @@ fn rematch_unsize<'tcx>( goal: Goal<'tcx, ty::TraitPredicate<'tcx>>, mut nested: Vec<PredicateObligation<'tcx>>, source: BuiltinImplSource, + certainty: Certainty, ) -> SelectionResult<'tcx, Selection<'tcx>> { let tcx = infcx.tcx; let a_ty = structurally_normalize(goal.predicate.self_ty(), infcx, goal.param_env, &mut nested); @@ -227,6 +236,12 @@ fn rematch_unsize<'tcx>( &mut nested, ); match (a_ty.kind(), b_ty.kind()) { + // Stall any ambiguous upcasting goals, since we can't rematch those + (ty::Dynamic(_, _, ty::Dyn), ty::Dynamic(_, _, ty::Dyn)) => match certainty { + Certainty::Yes => Ok(Some(ImplSource::Builtin(source, nested))), + _ => Ok(None), + }, + // `T` -> `dyn Trait` upcasting (_, &ty::Dynamic(data, region, ty::Dyn)) => { // Check that the type implements all of the predicates of the def-id. // (i.e. the principal, all of the associated types match, and any auto traits) @@ -354,10 +369,10 @@ fn rematch_unsize<'tcx>( ); Ok(Some(ImplSource::Builtin(source, nested))) } - // FIXME: We *could* ICE here if either: - // 1. the certainty is `Certainty::Yes`, - // 2. we're in codegen (which should mean `Certainty::Yes`). - _ => Ok(None), + _ => { + assert_ne!(certainty, Certainty::Yes); + Ok(None) + } } } diff --git a/tests/ui/traits/trait-upcasting/upcast-through-struct-tail.current.stderr b/tests/ui/traits/trait-upcasting/upcast-through-struct-tail.current.stderr new file mode 100644 index 00000000000..9f0993d65a7 --- /dev/null +++ b/tests/ui/traits/trait-upcasting/upcast-through-struct-tail.current.stderr @@ -0,0 +1,13 @@ +error[E0658]: cannot cast `dyn A` to `dyn B`, trait upcasting coercion is experimental + --> $DIR/upcast-through-struct-tail.rs:10:5 + | +LL | x + | ^ + | + = note: see issue #65991 <https://github.com/rust-lang/rust/issues/65991> for more information + = help: add `#![feature(trait_upcasting)]` to the crate attributes to enable + = note: required when coercing `Box<Wrapper<(dyn A + 'a)>>` into `Box<Wrapper<(dyn B + 'a)>>` + +error: aborting due to previous error + +For more information about this error, try `rustc --explain E0658`. diff --git a/tests/ui/traits/trait-upcasting/upcast-through-struct-tail.next.stderr b/tests/ui/traits/trait-upcasting/upcast-through-struct-tail.next.stderr new file mode 100644 index 00000000000..9f0993d65a7 --- /dev/null +++ b/tests/ui/traits/trait-upcasting/upcast-through-struct-tail.next.stderr @@ -0,0 +1,13 @@ +error[E0658]: cannot cast `dyn A` to `dyn B`, trait upcasting coercion is experimental + --> $DIR/upcast-through-struct-tail.rs:10:5 + | +LL | x + | ^ + | + = note: see issue #65991 <https://github.com/rust-lang/rust/issues/65991> for more information + = help: add `#![feature(trait_upcasting)]` to the crate attributes to enable + = note: required when coercing `Box<Wrapper<(dyn A + 'a)>>` into `Box<Wrapper<(dyn B + 'a)>>` + +error: aborting due to previous error + +For more information about this error, try `rustc --explain E0658`. diff --git a/tests/ui/traits/trait-upcasting/upcast-through-struct-tail.rs b/tests/ui/traits/trait-upcasting/upcast-through-struct-tail.rs new file mode 100644 index 00000000000..42495f45f8a --- /dev/null +++ b/tests/ui/traits/trait-upcasting/upcast-through-struct-tail.rs @@ -0,0 +1,14 @@ +// revisions: current next +//[next] compile-flags: -Ztrait-solver=next + +struct Wrapper<T: ?Sized>(T); + +trait A: B {} +trait B {} + +fn test<'a>(x: Box<Wrapper<dyn A + 'a>>) -> Box<Wrapper<dyn B + 'a>> { + x + //~^ ERROR cannot cast `dyn A` to `dyn B`, trait upcasting coercion is experimental +} + +fn main() {} |