| use rustc_data_structures::fx::FxHashSet; |
| use rustc_hir as hir; |
| use rustc_middle::ty::{self, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitor}; |
| use rustc_span::Span; |
| use std::ops::ControlFlow; |
| |
| /// This method traverses the structure of `ty`, trying to find an |
| /// instance of an ADT (i.e. struct or enum) that doesn't implement |
| /// the structural-match traits, or a generic type parameter |
| /// (which cannot be determined to be structural-match). |
| /// |
| /// The "structure of a type" includes all components that would be |
| /// considered when doing a pattern match on a constant of that |
| /// type. |
| /// |
| /// * This means this method descends into fields of structs/enums, |
| /// and also descends into the inner type `T` of `&T` and `&mut T` |
| /// |
| /// * The traversal doesn't dereference unsafe pointers (`*const T`, |
| /// `*mut T`), and it does not visit the type arguments of an |
| /// instantiated generic like `PhantomData<T>`. |
| /// |
| /// The reason we do this search is Rust currently require all ADTs |
| /// reachable from a constant's type to implement the |
| /// structural-match traits, which essentially say that |
| /// the implementation of `PartialEq::eq` behaves *equivalently* to a |
| /// comparison against the unfolded structure. |
| /// |
| /// For more background on why Rust has this requirement, and issues |
| /// that arose when the requirement was not enforced completely, see |
| /// Rust RFC 1445, rust-lang/rust#61188, and rust-lang/rust#62307. |
| pub fn search_for_structural_match_violation<'tcx>( |
| span: Span, |
| tcx: TyCtxt<'tcx>, |
| ty: Ty<'tcx>, |
| ) -> Option<Ty<'tcx>> { |
| ty.visit_with(&mut Search { tcx, span, seen: FxHashSet::default() }).break_value() |
| } |
| |
| /// This implements the traversal over the structure of a given type to try to |
| /// find instances of ADTs (specifically structs or enums) that do not implement |
| /// the structural-match traits (`StructuralPartialEq` and `StructuralEq`). |
| struct Search<'tcx> { |
| span: Span, |
| |
| tcx: TyCtxt<'tcx>, |
| |
| /// Tracks ADTs previously encountered during search, so that |
| /// we will not recur on them again. |
| seen: FxHashSet<hir::def_id::DefId>, |
| } |
| |
| impl<'tcx> Search<'tcx> { |
| fn type_marked_structural(&self, adt_ty: Ty<'tcx>) -> bool { |
| adt_ty.is_structural_eq_shallow(self.tcx) |
| } |
| } |
| |
| impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for Search<'tcx> { |
| type BreakTy = Ty<'tcx>; |
| |
| fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> { |
| debug!("Search visiting ty: {:?}", ty); |
| |
| let (adt_def, args) = match *ty.kind() { |
| ty::Adt(adt_def, args) => (adt_def, args), |
| ty::Param(_) => { |
| return ControlFlow::Break(ty); |
| } |
| ty::Dynamic(..) => { |
| return ControlFlow::Break(ty); |
| } |
| ty::Foreign(_) => { |
| return ControlFlow::Break(ty); |
| } |
| ty::Alias(..) => { |
| return ControlFlow::Break(ty); |
| } |
| ty::Closure(..) => { |
| return ControlFlow::Break(ty); |
| } |
| ty::Coroutine(..) | ty::CoroutineWitness(..) => { |
| return ControlFlow::Break(ty); |
| } |
| ty::FnDef(..) => { |
| // Types of formals and return in `fn(_) -> _` are also irrelevant; |
| // so we do not recur into them via `super_visit_with` |
| return ControlFlow::Continue(()); |
| } |
| ty::Array(_, n) |
| if { n.try_eval_target_usize(self.tcx, ty::ParamEnv::reveal_all()) == Some(0) } => |
| { |
| // rust-lang/rust#62336: ignore type of contents |
| // for empty array. |
| return ControlFlow::Continue(()); |
| } |
| ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Str | ty::Never => { |
| // These primitive types are always structural match. |
| // |
| // `Never` is kind of special here, but as it is not inhabitable, this should be fine. |
| return ControlFlow::Continue(()); |
| } |
| |
| ty::FnPtr(..) => { |
| return ControlFlow::Continue(()); |
| } |
| |
| ty::RawPtr(..) => { |
| // structural-match ignores substructure of |
| // `*const _`/`*mut _`, so skip `super_visit_with`. |
| // |
| // For example, if you have: |
| // ``` |
| // struct NonStructural; |
| // #[derive(PartialEq, Eq)] |
| // struct T(*const NonStructural); |
| // const C: T = T(std::ptr::null()); |
| // ``` |
| // |
| // Even though `NonStructural` does not implement `PartialEq`, |
| // structural equality on `T` does not recur into the raw |
| // pointer. Therefore, one can still use `C` in a pattern. |
| return ControlFlow::Continue(()); |
| } |
| |
| ty::Float(_) => { |
| return ControlFlow::Continue(()); |
| } |
| |
| ty::Array(..) | ty::Slice(_) | ty::Ref(..) | ty::Tuple(..) => { |
| // First check all contained types and then tell the caller to continue searching. |
| return ty.super_visit_with(self); |
| } |
| ty::Infer(_) | ty::Placeholder(_) | ty::Bound(..) => { |
| bug!("unexpected type during structural-match checking: {:?}", ty); |
| } |
| ty::Error(_) => { |
| self.tcx.sess.delay_span_bug(self.span, "ty::Error in structural-match check"); |
| // We still want to check other types after encountering an error, |
| // as this may still emit relevant errors. |
| return ControlFlow::Continue(()); |
| } |
| }; |
| |
| if !self.seen.insert(adt_def.did()) { |
| debug!("Search already seen adt_def: {:?}", adt_def); |
| return ControlFlow::Continue(()); |
| } |
| |
| if !self.type_marked_structural(ty) { |
| debug!("Search found ty: {:?}", ty); |
| return ControlFlow::Break(ty); |
| } |
| |
| // structural-match does not care about the |
| // instantiation of the generics in an ADT (it |
| // instead looks directly at its fields outside |
| // this match), so we skip super_visit_with. |
| // |
| // (Must not recur on args for `PhantomData<T>` cf |
| // rust-lang/rust#55028 and rust-lang/rust#55837; but also |
| // want to skip args when only uses of generic are |
| // behind unsafe pointers `*const T`/`*mut T`.) |
| |
| // even though we skip super_visit_with, we must recur on |
| // fields of ADT. |
| let tcx = self.tcx; |
| adt_def.all_fields().map(|field| field.ty(tcx, args)).try_for_each(|field_ty| { |
| let ty = self.tcx.normalize_erasing_regions(ty::ParamEnv::empty(), field_ty); |
| debug!("structural-match ADT: field_ty={:?}, ty={:?}", field_ty, ty); |
| ty.visit_with(self) |
| }) |
| } |
| } |