diff --git a/compiler/rustc_trait_selection/src/traits/coherence.rs b/compiler/rustc_trait_selection/src/traits/coherence.rs index 52ca23c4b303e..9983438233e1e 100644 --- a/compiler/rustc_trait_selection/src/traits/coherence.rs +++ b/compiler/rustc_trait_selection/src/traits/coherence.rs @@ -22,11 +22,12 @@ use rustc_middle::traits::specialization_graph::OverlapMode; use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams}; use rustc_middle::ty::subst::Subst; use rustc_middle::ty::visit::TypeVisitable; -use rustc_middle::ty::{self, ImplSubject, Ty, TyCtxt}; +use rustc_middle::ty::{self, ImplSubject, Ty, TyCtxt, TypeVisitor}; use rustc_span::symbol::sym; use rustc_span::DUMMY_SP; use std::fmt::Debug; use std::iter; +use std::ops::ControlFlow; /// Whether we do the orphan check relative to this crate or /// to some remote crate. @@ -578,220 +579,146 @@ fn orphan_check_trait_ref<'tcx>( ); } - // Given impl Trait for T0, an impl is valid only - // if at least one of the following is true: - // - // - Trait is a local trait - // (already checked in orphan_check prior to calling this function) - // - All of - // - At least one of the types T0..=Tn must be a local type. - // Let Ti be the first such type. - // - No uncovered type parameters P1..=Pn may appear in T0..Ti (excluding Ti) - // - fn uncover_fundamental_ty<'tcx>( - tcx: TyCtxt<'tcx>, - ty: Ty<'tcx>, - in_crate: InCrate, - ) -> Vec> { - // FIXME: this is currently somewhat overly complicated, - // but fixing this requires a more complicated refactor. - if !contained_non_local_types(tcx, ty, in_crate).is_empty() { - if let Some(inner_tys) = fundamental_ty_inner_tys(tcx, ty) { - return inner_tys - .flat_map(|ty| uncover_fundamental_ty(tcx, ty, in_crate)) - .collect(); + let mut checker = OrphanChecker::new(tcx, in_crate); + match trait_ref.visit_with(&mut checker) { + ControlFlow::Continue(()) => Err(OrphanCheckErr::NonLocalInputType(checker.non_local_tys)), + ControlFlow::Break(OrphanCheckEarlyExit::ParamTy(ty)) => { + // Does there exist some local type after the `ParamTy`. + checker.search_first_local_ty = true; + if let Some(OrphanCheckEarlyExit::LocalTy(local_ty)) = + trait_ref.visit_with(&mut checker).break_value() + { + Err(OrphanCheckErr::UncoveredTy(ty, Some(local_ty))) + } else { + Err(OrphanCheckErr::UncoveredTy(ty, None)) } } - - vec![ty] - } - - let mut non_local_spans = vec![]; - for (i, input_ty) in trait_ref - .substs - .types() - .flat_map(|ty| uncover_fundamental_ty(tcx, ty, in_crate)) - .enumerate() - { - debug!("orphan_check_trait_ref: check ty `{:?}`", input_ty); - let non_local_tys = contained_non_local_types(tcx, input_ty, in_crate); - if non_local_tys.is_empty() { - debug!("orphan_check_trait_ref: ty_is_local `{:?}`", input_ty); - return Ok(()); - } else if let ty::Param(_) = input_ty.kind() { - debug!("orphan_check_trait_ref: uncovered ty: `{:?}`", input_ty); - let local_type = trait_ref - .substs - .types() - .flat_map(|ty| uncover_fundamental_ty(tcx, ty, in_crate)) - .find(|&ty| ty_is_local_constructor(tcx, ty, in_crate)); - - debug!("orphan_check_trait_ref: uncovered ty local_type: `{:?}`", local_type); - - return Err(OrphanCheckErr::UncoveredTy(input_ty, local_type)); - } - - non_local_spans.extend(non_local_tys.into_iter().map(|input_ty| (input_ty, i == 0))); + ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(_)) => Ok(()), } - // If we exit above loop, never found a local type. - debug!("orphan_check_trait_ref: no local type"); - Err(OrphanCheckErr::NonLocalInputType(non_local_spans)) } -/// Returns a list of relevant non-local types for `ty`. -/// -/// This is just `ty` itself unless `ty` is `#[fundamental]`, -/// in which case we recursively look into this type. -/// -/// If `ty` is local itself, this method returns an empty `Vec`. -/// -/// # Examples -/// -/// - `u32` is not local, so this returns `[u32]`. -/// - for `Foo`, where `Foo` is a local type, this returns `[]`. -/// - `&mut u32` returns `[u32]`, as `&mut` is a fundamental type, similar to `Box`. -/// - `Box>` returns `[]`, as `Box` is a fundamental type and `Foo` is local. -fn contained_non_local_types<'tcx>( +struct OrphanChecker<'tcx> { tcx: TyCtxt<'tcx>, - ty: Ty<'tcx>, in_crate: InCrate, -) -> Vec> { - if ty_is_local_constructor(tcx, ty, in_crate) { - Vec::new() - } else { - match fundamental_ty_inner_tys(tcx, ty) { - Some(inner_tys) => { - inner_tys.flat_map(|ty| contained_non_local_types(tcx, ty, in_crate)).collect() - } - None => vec![ty], + in_self_ty: bool, + /// Ignore orphan check failures and exclusively search for the first + /// local type. + search_first_local_ty: bool, + non_local_tys: Vec<(Ty<'tcx>, bool)>, +} + +impl<'tcx> OrphanChecker<'tcx> { + fn new(tcx: TyCtxt<'tcx>, in_crate: InCrate) -> Self { + OrphanChecker { + tcx, + in_crate, + in_self_ty: true, + search_first_local_ty: false, + non_local_tys: Vec::new(), } } -} -/// For `#[fundamental]` ADTs and `&T` / `&mut T`, returns `Some` with the -/// type parameters of the ADT, or `T`, respectively. For non-fundamental -/// types, returns `None`. -fn fundamental_ty_inner_tys<'tcx>( - tcx: TyCtxt<'tcx>, - ty: Ty<'tcx>, -) -> Option>> { - let (first_ty, rest_tys) = match *ty.kind() { - ty::Ref(_, ty, _) => (ty, ty::subst::InternalSubsts::empty().types()), - ty::Adt(def, substs) if def.is_fundamental() => { - let mut types = substs.types(); - - // FIXME(eddyb) actually validate `#[fundamental]` up-front. - match types.next() { - None => { - tcx.sess.span_err( - tcx.def_span(def.did()), - "`#[fundamental]` requires at least one type parameter", - ); - - return None; - } + fn found_non_local_ty(&mut self, t: Ty<'tcx>) -> ControlFlow> { + self.non_local_tys.push((t, self.in_self_ty)); + ControlFlow::CONTINUE + } - Some(first_ty) => (first_ty, types), - } + fn found_param_ty(&mut self, t: Ty<'tcx>) -> ControlFlow> { + if self.search_first_local_ty { + ControlFlow::CONTINUE + } else { + ControlFlow::Break(OrphanCheckEarlyExit::ParamTy(t)) } - _ => return None, - }; + } - Some(iter::once(first_ty).chain(rest_tys)) + fn def_id_is_local(&mut self, def_id: DefId) -> bool { + match self.in_crate { + InCrate::Local => def_id.is_local(), + InCrate::Remote => false, + } + } } -fn def_id_is_local(def_id: DefId, in_crate: InCrate) -> bool { - match in_crate { - // The type is local to *this* crate - it will not be - // local in any other crate. - InCrate::Remote => false, - InCrate::Local => def_id.is_local(), - } +enum OrphanCheckEarlyExit<'tcx> { + ParamTy(Ty<'tcx>), + LocalTy(Ty<'tcx>), } -fn ty_is_local_constructor(tcx: TyCtxt<'_>, ty: Ty<'_>, in_crate: InCrate) -> bool { - debug!("ty_is_local_constructor({:?})", ty); - - match *ty.kind() { - ty::Bool - | ty::Char - | ty::Int(..) - | ty::Uint(..) - | ty::Float(..) - | ty::Str - | ty::FnDef(..) - | ty::FnPtr(_) - | ty::Array(..) - | ty::Slice(..) - | ty::RawPtr(..) - | ty::Ref(..) - | ty::Never - | ty::Tuple(..) - | ty::Param(..) - | ty::Projection(..) => false, - - ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) => match in_crate { - InCrate::Local => false, - // The inference variable might be unified with a local - // type in that remote crate. - InCrate::Remote => true, - }, - - ty::Adt(def, _) => def_id_is_local(def.did(), in_crate), - ty::Foreign(did) => def_id_is_local(did, in_crate), - ty::Opaque(..) => { - // This merits some explanation. - // Normally, opaque types are not involved when performing - // coherence checking, since it is illegal to directly - // implement a trait on an opaque type. However, we might - // end up looking at an opaque type during coherence checking - // if an opaque type gets used within another type (e.g. as - // a type parameter). This requires us to decide whether or - // not an opaque type should be considered 'local' or not. - // - // We choose to treat all opaque types as non-local, even - // those that appear within the same crate. This seems - // somewhat surprising at first, but makes sense when - // you consider that opaque types are supposed to hide - // the underlying type *within the same crate*. When an - // opaque type is used from outside the module - // where it is declared, it should be impossible to observe - // anything about it other than the traits that it implements. - // - // The alternative would be to look at the underlying type - // to determine whether or not the opaque type itself should - // be considered local. However, this could make it a breaking change - // to switch the underlying ('defining') type from a local type - // to a remote type. This would violate the rule that opaque - // types should be completely opaque apart from the traits - // that they implement, so we don't use this behavior. - false - } +impl<'tcx> TypeVisitor<'tcx> for OrphanChecker<'tcx> { + type BreakTy = OrphanCheckEarlyExit<'tcx>; + fn visit_region(&mut self, _r: ty::Region<'tcx>) -> ControlFlow { + ControlFlow::CONTINUE + } - ty::Dynamic(ref tt, ..) => { - if let Some(principal) = tt.principal() { - def_id_is_local(principal.def_id(), in_crate) - } else { - false + fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow { + let result = match *ty.kind() { + ty::Bool + | ty::Char + | ty::Int(..) + | ty::Uint(..) + | ty::Float(..) + | ty::Str + | ty::FnDef(..) + | ty::FnPtr(_) + | ty::Array(..) + | ty::Slice(..) + | ty::RawPtr(..) + | ty::Never + | ty::Tuple(..) + | ty::Projection(..) => self.found_non_local_ty(ty), + + ty::Param(..) => self.found_param_ty(ty), + + ty::Placeholder(..) | ty::Bound(..) | ty::Infer(..) => match self.in_crate { + InCrate::Local => self.found_non_local_ty(ty), + // The inference variable might be unified with a local + // type in that remote crate. + InCrate::Remote => ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty)), + }, + + // For fundamental types, we just look inside of them. + ty::Ref(_, ty, _) => ty.visit_with(self), + ty::Adt(def, substs) => { + if self.def_id_is_local(def.did()) { + ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty)) + } else if def.is_fundamental() { + substs.visit_with(self) + } else { + self.found_non_local_ty(ty) + } } - } + ty::Foreign(def_id) => { + if self.def_id_is_local(def_id) { + ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty)) + } else { + self.found_non_local_ty(ty) + } + } + ty::Dynamic(tt, ..) => { + let principal = tt.principal().map(|p| p.def_id()); + if principal.map_or(false, |p| self.def_id_is_local(p)) { + ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty)) + } else { + self.found_non_local_ty(ty) + } + } + ty::Error(_) => ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty)), + ty::Opaque(..) | ty::Closure(..) | ty::Generator(..) | ty::GeneratorWitness(..) => { + self.tcx.sess.delay_span_bug( + DUMMY_SP, + format!("ty_is_local invoked on closure or generator: {:?}", ty), + ); + ControlFlow::Break(OrphanCheckEarlyExit::LocalTy(ty)) + } + }; + // A bit of a hack, the `OrphanChecker` is only used to visit a `TraitRef`, so + // the first type we visit is always the self type. + self.in_self_ty = false; + result + } - ty::Error(_) => true, - - // These variants should never appear during coherence checking because they - // cannot be named directly. - // - // They could be indirectly used through an opaque type. While using opaque types - // in impls causes an error, this path can still be hit afterwards. - // - // See `test/ui/coherence/coherence-with-closure.rs` for an example where this - // could happens. - ty::Closure(..) | ty::Generator(..) | ty::GeneratorWitness(..) => { - tcx.sess.delay_span_bug( - DUMMY_SP, - format!("ty_is_local invoked on closure or generator: {:?}", ty), - ); - true - } + // FIXME: Constants should participate in orphan checking. + fn visit_const(&mut self, _c: ty::Const<'tcx>) -> ControlFlow { + ControlFlow::CONTINUE } } diff --git a/src/test/ui/impl-trait/negative-reasoning.stderr b/src/test/ui/impl-trait/negative-reasoning.stderr index 479b451855d55..2eea726a19c5a 100644 --- a/src/test/ui/impl-trait/negative-reasoning.stderr +++ b/src/test/ui/impl-trait/negative-reasoning.stderr @@ -7,7 +7,7 @@ LL | impl AnotherTrait for T {} LL | impl AnotherTrait for D { | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `D` | - = note: upstream crates may add a new impl of trait `std::fmt::Debug` for type `OpaqueType` in future versions + = note: downstream crates may implement trait `std::fmt::Debug` for type `OpaqueType` error: cannot implement trait on type alias impl trait --> $DIR/negative-reasoning.rs:19:25