diff options
| -rw-r--r-- | compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs | 145 | ||||
| -rw-r--r-- | tests/ui/traits/issue-24010.rs | 2 | ||||
| -rw-r--r-- | tests/ui/traits/new-solver/unsize-although-ambiguous.rs | 13 |
3 files changed, 159 insertions, 1 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 bf6cbef8c3b..f40202cf2c5 100644 --- a/compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs +++ b/compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs @@ -1,5 +1,6 @@ use std::ops::ControlFlow; +use rustc_hir as hir; use rustc_hir::def_id::DefId; use rustc_infer::infer::{DefineOpaqueTypes, InferCtxt, InferOk}; use rustc_infer::traits::util::supertraits; @@ -11,7 +12,7 @@ use rustc_middle::traits::{ ImplSource, ImplSourceObjectData, ImplSourceTraitUpcastingData, ImplSourceUserDefinedData, ObligationCause, SelectionError, }; -use rustc_middle::ty::{self, TyCtxt}; +use rustc_middle::ty::{self, Ty, TyCtxt}; use rustc_span::DUMMY_SP; use crate::solve::assembly::{BuiltinImplSource, Candidate, CandidateSource}; @@ -113,6 +114,12 @@ impl<'tcx> InferCtxtSelectExt<'tcx> for InferCtxt<'tcx> { ), ) => rematch_object(self, goal, nested_obligations), + (Certainty::Maybe(_), CandidateSource::BuiltinImpl(BuiltinImplSource::Misc)) + if self.tcx.lang_items().unsize_trait() == Some(goal.predicate.def_id()) => + { + rematch_unsize(self, goal, nested_obligations) + } + // Technically some builtin impls have nested obligations, but if // `Certainty::Yes`, then they should've all been verified and don't // need re-checking. @@ -232,6 +239,9 @@ fn rematch_object<'tcx>( { assert_eq!(source_kind, ty::Dyn, "cannot upcast dyn*"); if let ty::Dynamic(data, _, ty::Dyn) = goal.predicate.trait_ref.substs.type_at(1).kind() { + // FIXME: We also need to ensure that the source lifetime outlives the + // target lifetime. This doesn't matter for codegen, though, and only + // *really* matters if the goal's certainty is ambiguous. (true, data.principal().unwrap().with_self_ty(infcx.tcx, self_ty)) } else { bug!() @@ -305,3 +315,136 @@ fn rematch_object<'tcx>( ImplSource::Object(ImplSourceObjectData { vtable_base, nested }) })) } + +/// The `Unsize` trait is particularly important to coercion, so we try rematch it. +/// NOTE: This must stay in sync with `consider_builtin_unsize_candidate` in trait +/// goal assembly in the solver, both for soundness and in order to avoid ICEs. +fn rematch_unsize<'tcx>( + infcx: &InferCtxt<'tcx>, + goal: Goal<'tcx, ty::TraitPredicate<'tcx>>, + mut nested: Vec<PredicateObligation<'tcx>>, +) -> SelectionResult<'tcx, Selection<'tcx>> { + let tcx = infcx.tcx; + let a_ty = goal.predicate.self_ty(); + let b_ty = goal.predicate.trait_ref.substs.type_at(1); + + match (a_ty.kind(), b_ty.kind()) { + (_, &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) + nested.extend(data.iter().map(|pred| { + Obligation::new( + infcx.tcx, + ObligationCause::dummy(), + goal.param_env, + pred.with_self_ty(tcx, a_ty), + ) + })); + // The type must be Sized to be unsized. + let sized_def_id = tcx.require_lang_item(hir::LangItem::Sized, None); + nested.push(Obligation::new( + infcx.tcx, + ObligationCause::dummy(), + goal.param_env, + ty::TraitRef::new(tcx, sized_def_id, [a_ty]), + )); + // The type must outlive the lifetime of the `dyn` we're unsizing into. + nested.push(Obligation::new( + infcx.tcx, + ObligationCause::dummy(), + goal.param_env, + ty::Binder::dummy(ty::OutlivesPredicate(a_ty, region)), + )); + } + // `[T; n]` -> `[T]` unsizing + (&ty::Array(a_elem_ty, ..), &ty::Slice(b_elem_ty)) => { + nested.extend( + infcx + .at(&ObligationCause::dummy(), goal.param_env) + .eq(DefineOpaqueTypes::No, a_elem_ty, b_elem_ty) + .expect("expected rematch to succeed") + .into_obligations(), + ); + } + // Struct unsizing `Struct<T>` -> `Struct<U>` where `T: Unsize<U>` + (&ty::Adt(a_def, a_substs), &ty::Adt(b_def, b_substs)) + if a_def.is_struct() && a_def.did() == b_def.did() => + { + let unsizing_params = tcx.unsizing_params_for_adt(a_def.did()); + // We must be unsizing some type parameters. This also implies + // that the struct has a tail field. + if unsizing_params.is_empty() { + bug!("expected rematch to succeed") + } + + let tail_field = a_def + .non_enum_variant() + .fields + .raw + .last() + .expect("expected unsized ADT to have a tail field"); + let tail_field_ty = tcx.type_of(tail_field.did); + + let a_tail_ty = tail_field_ty.subst(tcx, a_substs); + let b_tail_ty = tail_field_ty.subst(tcx, b_substs); + + // Substitute just the unsizing params from B into A. The type after + // this substitution must be equal to B. This is so we don't unsize + // unrelated type parameters. + let new_a_substs = + tcx.mk_substs_from_iter(a_substs.iter().enumerate().map(|(i, a)| { + if unsizing_params.contains(i as u32) { b_substs[i] } else { a } + })); + let unsized_a_ty = Ty::new_adt(tcx, a_def, new_a_substs); + + nested.extend( + infcx + .at(&ObligationCause::dummy(), goal.param_env) + .eq(DefineOpaqueTypes::No, unsized_a_ty, b_ty) + .expect("expected rematch to succeed") + .into_obligations(), + ); + + // Finally, we require that `TailA: Unsize<TailB>` for the tail field + // types. + nested.push(Obligation::new( + tcx, + ObligationCause::dummy(), + goal.param_env, + ty::TraitRef::new(tcx, goal.predicate.def_id(), [a_tail_ty, b_tail_ty]), + )); + } + // Tuple unsizing `(.., T)` -> `(.., U)` where `T: Unsize<U>` + (&ty::Tuple(a_tys), &ty::Tuple(b_tys)) + if a_tys.len() == b_tys.len() && !a_tys.is_empty() => + { + let (a_last_ty, a_rest_tys) = a_tys.split_last().unwrap(); + let b_last_ty = b_tys.last().unwrap(); + + // Substitute just the tail field of B., and require that they're equal. + let unsized_a_ty = + Ty::new_tup_from_iter(tcx, a_rest_tys.iter().chain([b_last_ty]).copied()); + nested.extend( + infcx + .at(&ObligationCause::dummy(), goal.param_env) + .eq(DefineOpaqueTypes::No, unsized_a_ty, b_ty) + .expect("expected rematch to succeed") + .into_obligations(), + ); + + // Similar to ADTs, require that the rest of the fields are equal. + nested.push(Obligation::new( + tcx, + ObligationCause::dummy(), + goal.param_env, + ty::TraitRef::new(tcx, goal.predicate.def_id(), [*a_last_ty, *b_last_ty]), + )); + } + // FIXME: We *could* ICE here if either: + // 1. the certainty is `Certainty::Yes`, + // 2. we're in codegen (which should mean `Certainty::Yes`). + _ => return Ok(None), + } + + Ok(Some(ImplSource::Builtin(nested))) +} diff --git a/tests/ui/traits/issue-24010.rs b/tests/ui/traits/issue-24010.rs index f1818533487..fd7d6751d5c 100644 --- a/tests/ui/traits/issue-24010.rs +++ b/tests/ui/traits/issue-24010.rs @@ -1,4 +1,6 @@ // run-pass +// revisions: classic next +//[next] compile-flags: -Ztrait-solver=next trait Foo: Fn(i32) -> i32 + Send {} diff --git a/tests/ui/traits/new-solver/unsize-although-ambiguous.rs b/tests/ui/traits/new-solver/unsize-although-ambiguous.rs new file mode 100644 index 00000000000..431988a5fff --- /dev/null +++ b/tests/ui/traits/new-solver/unsize-although-ambiguous.rs @@ -0,0 +1,13 @@ +// check-pass +// compile-flags: -Ztrait-solver=next + +use std::fmt::Display; + +fn box_dyn_display(_: Box<dyn Display>) {} + +fn main() { + // During coercion, we don't necessarily know whether `{integer}` implements + // `Display`. Before, that would cause us to bail out in the coercion loop when + // checking `{integer}: Unsize<dyn Display>`. + box_dyn_display(Box::new(1)); +} |