Add query to deterimine if type implements StructuralEq

Author: ecstatic-morse

src/librustc_middle/query/mod.rs

@@ -719,6 +719,11 @@ rustc_queries! {
             desc { "computing whether `{}` needs drop", env.value }
         }
 
+        /// Query backing `TyS::is_structural_eq_shallow`.
+        query is_structural_eq_raw(ty: Ty<'tcx>) -> bool {
+            desc { "computing whether `{:?}` has a derived implementation of `PartialEq` and `Eq`", ty }
+        }
+
         /// A list of types where the ADT requires drop if and only if any of
         /// those types require drop. If the ADT is known to always need drop
         /// then `Err(AlwaysRequiresDrop)` is returned.

src/librustc_middle/ty/util.rs

@@ -778,6 +778,27 @@ impl<'tcx> ty::TyS<'tcx> {
         }
     }
 
+    /// Returns `true` if this type implements both `PartialStructuralEq` and `StructuralEq`.
+    ///
+    /// These marker traits are implemented along with `PartialEq` and `Eq` when implementations
+    /// for those traits are derived. They indicate that two values of this type are equal if all
+    /// of their fields are equal. A quirk of the marker traits is that their implementation is
+    /// never conditional on generic parameter bounds. For that reason, this helper function does
+    /// not take a `ParamEnv`.
+    ///
+    /// This function is "shallow" because it may return `true` for a type whose fields are not
+    /// `StructuralEq`. You will need to use a type visitor if you want to know whether a call to
+    /// `PartialEq::eq` will proceed structurally for a given type.
+    #[inline]
+    pub fn is_structural_eq_shallow(&'tcx self, tcx: TyCtxt<'tcx>) -> bool {
+        // Fast path for some builtin types
+        if self.is_primitive() || self.is_str() {
+            return true;
+        }
+
+        tcx.is_structural_eq_raw(self)
+    }
+
     pub fn same_type(a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
         match (&a.kind, &b.kind) {
             (&Adt(did_a, substs_a), &Adt(did_b, substs_b)) => {

src/librustc_mir/transform/check_consts/qualifs.rs

@@ -2,7 +2,6 @@
 //!
 //! See the `Qualif` trait for more info.
 
-use rustc_infer::infer::TyCtxtInferExt;
 use rustc_middle::mir::*;
 use rustc_middle::ty::{self, subst::SubstsRef, AdtDef, Ty};
 use rustc_span::DUMMY_SP;
@@ -137,10 +136,7 @@ impl Qualif for CustomEq {
         substs: SubstsRef<'tcx>,
     ) -> bool {
         let ty = cx.tcx.mk_ty(ty::Adt(adt, substs));
-        let id = cx.tcx.hir().local_def_id_to_hir_id(cx.def_id.as_local().unwrap());
-        cx.tcx
-            .infer_ctxt()
-            .enter(|infcx| !traits::type_marked_structural(id, cx.body.span, &infcx, ty))
+        !ty.is_structural_eq_shallow(cx.tcx)
     }
 }
 

src/librustc_mir_build/hair/pattern/const_to_pat.rs

@@ -80,7 +80,7 @@ impl<'a, 'tcx> ConstToPat<'a, 'tcx> {
     }
 
     fn type_marked_structural(&self, ty: Ty<'tcx>) -> bool {
-        traits::type_marked_structural(self.id, self.span, &self.infcx, ty)
+        ty.is_structural_eq_shallow(self.infcx.tcx)
     }
 
     fn to_pat(

src/librustc_trait_selection/traits/mod.rs

@@ -564,6 +564,7 @@ fn type_implements_trait<'tcx>(
 
 pub fn provide(providers: &mut ty::query::Providers<'_>) {
     object_safety::provide(providers);
+    structural_match::provide(providers);
     *providers = ty::query::Providers {
         specialization_graph_of: specialize::specialization_graph_provider,
         specializes: specialize::specializes,

src/librustc_trait_selection/traits/structural_match.rs

@@ -1,10 +1,11 @@
 use crate::infer::{InferCtxt, TyCtxtInferExt};
 use crate::traits::ObligationCause;
-use crate::traits::{self, ConstPatternStructural, TraitEngine};
+use crate::traits::{self, TraitEngine};
 
 use rustc_data_structures::fx::FxHashSet;
 use rustc_hir as hir;
 use rustc_hir::lang_items::{StructuralPeqTraitLangItem, StructuralTeqTraitLangItem};
+use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::{self, AdtDef, Ty, TyCtxt, TypeFoldable, TypeVisitor};
 use rustc_span::Span;
 
@@ -41,14 +42,14 @@ pub enum NonStructuralMatchTy<'tcx> {
 /// 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>(
-    id: hir::HirId,
-    span: Span,
+    _id: hir::HirId,
+    _span: Span,
     tcx: TyCtxt<'tcx>,
     ty: Ty<'tcx>,
 ) -> Option<NonStructuralMatchTy<'tcx>> {
     // FIXME: we should instead pass in an `infcx` from the outside.
     tcx.infer_ctxt().enter(|infcx| {
-        let mut search = Search { id, span, infcx, found: None, seen: FxHashSet::default() };
+        let mut search = Search { infcx, found: None, seen: FxHashSet::default() };
         ty.visit_with(&mut search);
         search.found
     })
@@ -62,26 +63,25 @@ pub fn search_for_structural_match_violation<'tcx>(
 /// Note that this does *not* recursively check if the substructure of `adt_ty`
 /// implements the traits.
 pub fn type_marked_structural(
-    id: hir::HirId,
-    span: Span,
     infcx: &InferCtxt<'_, 'tcx>,
     adt_ty: Ty<'tcx>,
+    cause: ObligationCause<'tcx>,
 ) -> bool {
     let mut fulfillment_cx = traits::FulfillmentContext::new();
-    let cause = ObligationCause::new(span, id, ConstPatternStructural);
     // require `#[derive(PartialEq)]`
-    let structural_peq_def_id = infcx.tcx.require_lang_item(StructuralPeqTraitLangItem, Some(span));
+    let structural_peq_def_id =
+        infcx.tcx.require_lang_item(StructuralPeqTraitLangItem, Some(cause.span));
     fulfillment_cx.register_bound(
         infcx,
         ty::ParamEnv::empty(),
         adt_ty,
         structural_peq_def_id,
-        cause,
+        cause.clone(),
     );
     // for now, require `#[derive(Eq)]`. (Doing so is a hack to work around
     // the type `for<'a> fn(&'a ())` failing to implement `Eq` itself.)
-    let cause = ObligationCause::new(span, id, ConstPatternStructural);
-    let structural_teq_def_id = infcx.tcx.require_lang_item(StructuralTeqTraitLangItem, Some(span));
+    let structural_teq_def_id =
+        infcx.tcx.require_lang_item(StructuralTeqTraitLangItem, Some(cause.span));
     fulfillment_cx.register_bound(
         infcx,
         ty::ParamEnv::empty(),
@@ -106,9 +106,6 @@ pub fn type_marked_structural(
 /// find instances of ADTs (specifically structs or enums) that do not implement
 /// the structural-match traits (`StructuralPartialEq` and `StructuralEq`).
 struct Search<'a, 'tcx> {
-    id: hir::HirId,
-    span: Span,
-
     infcx: InferCtxt<'a, 'tcx>,
 
     /// Records first ADT that does not implement a structural-match trait.
@@ -125,7 +122,7 @@ impl Search<'a, 'tcx> {
     }
 
     fn type_marked_structural(&self, adt_ty: Ty<'tcx>) -> bool {
-        type_marked_structural(self.id, self.span, &self.infcx, adt_ty)
+        adt_ty.is_structural_eq_shallow(self.tcx())
     }
 }
 
@@ -220,3 +217,12 @@ impl<'a, 'tcx> TypeVisitor<'tcx> for Search<'a, 'tcx> {
         false
     }
 }
+
+pub fn provide(providers: &mut Providers<'_>) {
+    providers.is_structural_eq_raw = |tcx, ty| {
+        tcx.infer_ctxt().enter(|infcx| {
+            let cause = ObligationCause::dummy();
+            type_marked_structural(&infcx, ty, cause)
+        })
+    };
+}