1 use crate::infer::{InferCtxt, TyCtxtInferExt};
2 use crate::traits::ObligationCause;
3 use crate::traits::{self, TraitEngine};
5 use rustc_data_structures::fx::FxHashSet;
7 use rustc_hir::lang_items::LangItem;
8 use rustc_middle::ty::query::Providers;
9 use rustc_middle::ty::{self, AdtDef, Ty, TyCtxt, TypeFoldable, TypeVisitor};
11 use std::ops::ControlFlow;
14 pub struct NonStructuralMatchTy<'tcx> {
16 pub kind: NonStructuralMatchTyKind<'tcx>,
20 pub enum NonStructuralMatchTyKind<'tcx> {
31 /// This method traverses the structure of `ty`, trying to find an
32 /// instance of an ADT (i.e. struct or enum) that doesn't implement
33 /// the structural-match traits, or a generic type parameter
34 /// (which cannot be determined to be structural-match).
36 /// The "structure of a type" includes all components that would be
37 /// considered when doing a pattern match on a constant of that
40 /// * This means this method descends into fields of structs/enums,
41 /// and also descends into the inner type `T` of `&T` and `&mut T`
43 /// * The traversal doesn't dereference unsafe pointers (`*const T`,
44 /// `*mut T`), and it does not visit the type arguments of an
45 /// instantiated generic like `PhantomData<T>`.
47 /// The reason we do this search is Rust currently require all ADTs
48 /// reachable from a constant's type to implement the
49 /// structural-match traits, which essentially say that
50 /// the implementation of `PartialEq::eq` behaves *equivalently* to a
51 /// comparison against the unfolded structure.
53 /// For more background on why Rust has this requirement, and issues
54 /// that arose when the requirement was not enforced completely, see
55 /// Rust RFC 1445, rust-lang/rust#61188, and rust-lang/rust#62307.
56 pub fn search_for_structural_match_violation<'tcx>(
60 ) -> Option<NonStructuralMatchTy<'tcx>> {
61 // FIXME: we should instead pass in an `infcx` from the outside.
62 tcx.infer_ctxt().enter(|infcx| {
63 ty.visit_with(&mut Search { infcx, span, seen: FxHashSet::default() }).break_value()
67 /// This method returns true if and only if `adt_ty` itself has been marked as
68 /// eligible for structural-match: namely, if it implements both
69 /// `StructuralPartialEq` and `StructuralEq` (which are respectively injected by
70 /// `#[derive(PartialEq)]` and `#[derive(Eq)]`).
72 /// Note that this does *not* recursively check if the substructure of `adt_ty`
73 /// implements the traits.
74 fn type_marked_structural<'tcx>(
75 infcx: &InferCtxt<'_, 'tcx>,
77 cause: ObligationCause<'tcx>,
79 let mut fulfillment_cx = traits::FulfillmentContext::new();
80 // require `#[derive(PartialEq)]`
81 let structural_peq_def_id =
82 infcx.tcx.require_lang_item(LangItem::StructuralPeq, Some(cause.span));
83 fulfillment_cx.register_bound(
85 ty::ParamEnv::empty(),
87 structural_peq_def_id,
90 // for now, require `#[derive(Eq)]`. (Doing so is a hack to work around
91 // the type `for<'a> fn(&'a ())` failing to implement `Eq` itself.)
92 let structural_teq_def_id =
93 infcx.tcx.require_lang_item(LangItem::StructuralTeq, Some(cause.span));
94 fulfillment_cx.register_bound(
96 ty::ParamEnv::empty(),
98 structural_teq_def_id,
102 // We deliberately skip *reporting* fulfillment errors (via
103 // `report_fulfillment_errors`), for two reasons:
105 // 1. The error messages would mention `std::marker::StructuralPartialEq`
106 // (a trait which is solely meant as an implementation detail
109 // 2. We are sometimes doing future-incompatibility lints for
110 // now, so we do not want unconditional errors here.
111 fulfillment_cx.select_all_or_error(infcx).is_empty()
114 /// This implements the traversal over the structure of a given type to try to
115 /// find instances of ADTs (specifically structs or enums) that do not implement
116 /// the structural-match traits (`StructuralPartialEq` and `StructuralEq`).
117 struct Search<'a, 'tcx> {
120 infcx: InferCtxt<'a, 'tcx>,
122 /// Tracks ADTs previously encountered during search, so that
123 /// we will not recur on them again.
124 seen: FxHashSet<hir::def_id::DefId>,
127 impl<'a, 'tcx> Search<'a, 'tcx> {
128 fn tcx(&self) -> TyCtxt<'tcx> {
132 fn type_marked_structural(&self, adt_ty: Ty<'tcx>) -> bool {
133 adt_ty.is_structural_eq_shallow(self.tcx())
137 impl<'a, 'tcx> TypeVisitor<'tcx> for Search<'a, 'tcx> {
138 type BreakTy = NonStructuralMatchTy<'tcx>;
140 fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
141 debug!("Search visiting ty: {:?}", ty);
143 let (adt_def, substs) = match *ty.kind() {
144 ty::Adt(adt_def, substs) => (adt_def, substs),
146 let kind = NonStructuralMatchTyKind::Param;
147 return ControlFlow::Break(NonStructuralMatchTy { ty, kind });
150 let kind = NonStructuralMatchTyKind::Dynamic;
151 return ControlFlow::Break(NonStructuralMatchTy { ty, kind });
154 let kind = NonStructuralMatchTyKind::Foreign;
155 return ControlFlow::Break(NonStructuralMatchTy { ty, kind });
158 let kind = NonStructuralMatchTyKind::Opaque;
159 return ControlFlow::Break(NonStructuralMatchTy { ty, kind });
161 ty::Projection(..) => {
162 let kind = NonStructuralMatchTyKind::Projection;
163 return ControlFlow::Break(NonStructuralMatchTy { ty, kind });
166 let kind = NonStructuralMatchTyKind::Closure;
167 return ControlFlow::Break(NonStructuralMatchTy { ty, kind });
169 ty::Generator(..) | ty::GeneratorWitness(..) => {
170 let kind = NonStructuralMatchTyKind::Generator;
171 return ControlFlow::Break(NonStructuralMatchTy { ty, kind });
174 // structural-match ignores substructure of
175 // `*const _`/`*mut _`, so skip `super_visit_with`.
177 // For example, if you have:
179 // struct NonStructural;
180 // #[derive(PartialEq, Eq)]
181 // struct T(*const NonStructural);
182 // const C: T = T(std::ptr::null());
185 // Even though `NonStructural` does not implement `PartialEq`,
186 // structural equality on `T` does not recur into the raw
187 // pointer. Therefore, one can still use `C` in a pattern.
188 return ControlFlow::CONTINUE;
190 ty::FnDef(..) | ty::FnPtr(..) => {
191 // Types of formals and return in `fn(_) -> _` are also irrelevant;
192 // so we do not recur into them via `super_visit_with`
193 return ControlFlow::CONTINUE;
196 if { n.try_eval_usize(self.tcx(), ty::ParamEnv::reveal_all()) == Some(0) } =>
198 // rust-lang/rust#62336: ignore type of contents
200 return ControlFlow::CONTINUE;
202 ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Str | ty::Never => {
203 // These primitive types are always structural match.
205 // `Never` is kind of special here, but as it is not inhabitable, this should be fine.
206 return ControlFlow::CONTINUE;
209 ty::Array(..) | ty::Slice(_) | ty::Ref(..) | ty::Tuple(..) => {
210 // First check all contained types and then tell the caller to continue searching.
211 return ty.super_visit_with(self);
213 ty::Infer(_) | ty::Placeholder(_) | ty::Bound(..) => {
214 bug!("unexpected type during structural-match checking: {:?}", ty);
217 self.tcx().sess.delay_span_bug(self.span, "ty::Error in structural-match check");
218 // We still want to check other types after encountering an error,
219 // as this may still emit relevant errors.
220 return ControlFlow::CONTINUE;
224 if !self.seen.insert(adt_def.did()) {
225 debug!("Search already seen adt_def: {:?}", adt_def);
226 return ControlFlow::CONTINUE;
229 if !self.type_marked_structural(ty) {
230 debug!("Search found ty: {:?}", ty);
231 let kind = NonStructuralMatchTyKind::Adt(adt_def);
232 return ControlFlow::Break(NonStructuralMatchTy { ty, kind });
235 // structural-match does not care about the
236 // instantiation of the generics in an ADT (it
237 // instead looks directly at its fields outside
238 // this match), so we skip super_visit_with.
240 // (Must not recur on substs for `PhantomData<T>` cf
241 // rust-lang/rust#55028 and rust-lang/rust#55837; but also
242 // want to skip substs when only uses of generic are
243 // behind unsafe pointers `*const T`/`*mut T`.)
245 // even though we skip super_visit_with, we must recur on
247 let tcx = self.tcx();
248 adt_def.all_fields().map(|field| field.ty(tcx, substs)).try_for_each(|field_ty| {
249 let ty = self.tcx().normalize_erasing_regions(ty::ParamEnv::empty(), field_ty);
250 debug!("structural-match ADT: field_ty={:?}, ty={:?}", field_ty, ty);
256 pub fn provide(providers: &mut Providers) {
257 providers.has_structural_eq_impls = |tcx, ty| {
258 tcx.infer_ctxt().enter(|infcx| {
259 let cause = ObligationCause::dummy();
260 type_marked_structural(&infcx, ty, cause)