remove StructuralEq trait

Author: RalfJung

compiler/rustc_builtin_macros/src/deriving/cmp/eq.rs

@@ -19,19 +19,6 @@ pub fn expand_deriving_eq(
 ) {
     let span = cx.with_def_site_ctxt(span);
 
-    let structural_trait_def = TraitDef {
-        span,
-        path: path_std!(marker::StructuralEq),
-        skip_path_as_bound: true, // crucial!
-        needs_copy_as_bound_if_packed: false,
-        additional_bounds: Vec::new(),
-        supports_unions: true,
-        methods: Vec::new(),
-        associated_types: Vec::new(),
-        is_const: false,
-    };
-    structural_trait_def.expand(cx, mitem, item, push);
-
     let trait_def = TraitDef {
         span,
         path: path_std!(cmp::Eq),

compiler/rustc_codegen_cranelift/example/mini_core.rs

@@ -104,9 +104,6 @@ unsafe impl<T: ?Sized> Freeze for &mut T {}
 #[lang = "structural_peq"]
 pub trait StructuralPartialEq {}
 
-#[lang = "structural_teq"]
-pub trait StructuralEq {}
-
 #[lang = "not"]
 pub trait Not {
     type Output;

compiler/rustc_codegen_gcc/example/mini_core.rs

@@ -100,9 +100,6 @@ unsafe impl<T: ?Sized> Freeze for &mut T {}
 #[lang = "structural_peq"]
 pub trait StructuralPartialEq {}
 
-#[lang = "structural_teq"]
-pub trait StructuralEq {}
-
 #[lang = "not"]
 pub trait Not {
     type Output;

compiler/rustc_codegen_gcc/tests/run/static.rs

@@ -60,9 +60,6 @@ mod libc {
 #[lang = "structural_peq"]
 pub trait StructuralPartialEq {}
 
-#[lang = "structural_teq"]
-pub trait StructuralEq {}
-
 #[lang = "drop_in_place"]
 #[allow(unconditional_recursion)]
 pub unsafe fn drop_in_place<T: ?Sized>(to_drop: *mut T) {

compiler/rustc_const_eval/src/const_eval/valtrees.rs

@@ -117,7 +117,7 @@ pub(crate) fn const_to_valtree_inner<'tcx>(
         }
         // Trait objects are not allowed in type level constants, as we have no concept for
         // resolving their backing type, even if we can do that at const eval time. We may
-        // hypothetically be able to allow `dyn StructuralEq` trait objects in the future,
+        // hypothetically be able to allow `dyn StructuralPartialEq` trait objects in the future,
         // but it is unclear if this is useful.
         ty::Dynamic(..) => Err(ValTreeCreationError::NonSupportedType),
 

compiler/rustc_hir/src/lang_items.rs

@@ -143,8 +143,6 @@ language_item_table! {
     Unsize,                  sym::unsize,              unsize_trait,               Target::Trait,          GenericRequirement::Minimum(1);
     /// Trait injected by `#[derive(PartialEq)]`, (i.e. "Partial EQ").
     StructuralPeq,           sym::structural_peq,      structural_peq_trait,       Target::Trait,          GenericRequirement::None;
-    /// Trait injected by `#[derive(Eq)]`, (i.e. "Total EQ"; no, I will not apologize).
-    StructuralTeq,           sym::structural_teq,      structural_teq_trait,       Target::Trait,          GenericRequirement::None;
     Copy,                    sym::copy,                copy_trait,                 Target::Trait,          GenericRequirement::Exact(0);
     Clone,                   sym::clone,               clone_trait,                Target::Trait,          GenericRequirement::None;
     Sync,                    sym::sync,                sync_trait,                 Target::Trait,          GenericRequirement::Exact(0);

compiler/rustc_middle/src/query/mod.rs

@@ -1359,9 +1359,9 @@ rustc_queries! {
     ///
     /// This is only correct for ADTs. Call `is_structural_eq_shallow` to handle all types
     /// correctly.
-    query has_structural_eq_impls(ty: Ty<'tcx>) -> bool {
+    query has_structural_eq_impl(ty: Ty<'tcx>) -> bool {
         desc {
-            "computing whether `{}` implements `PartialStructuralEq` and `StructuralEq`",
+            "computing whether `{}` implements `PartialStructuralEq`",
             ty
         }
     }

compiler/rustc_middle/src/ty/util.rs

@@ -1150,19 +1150,18 @@ impl<'tcx> Ty<'tcx> {
     /// Primitive types (`u32`, `str`) have structural equality by definition. For composite data
     /// types, equality for the type as a whole is structural when it is the same as equality
     /// between all components (fields, array elements, etc.) of that type. For ADTs, structural
-    /// equality is indicated by an implementation of `PartialStructuralEq` and `StructuralEq` for
-    /// that type.
+    /// equality is indicated by an implementation of `PartialStructuralEq` for that type.
     ///
     /// This function is "shallow" because it may return `true` for a composite type whose fields
-    /// are not `StructuralEq`. For example, `[T; 4]` has structural equality regardless of `T`
+    /// are not `StructuralPartialEq`. For example, `[T; 4]` has structural equality regardless of `T`
     /// because equality for arrays is determined by the equality of each array element. If you
     /// want to know whether a given call to `PartialEq::eq` will proceed structurally all the way
     /// down, you will need to use a type visitor.
     #[inline]
     pub fn is_structural_eq_shallow(self, tcx: TyCtxt<'tcx>) -> bool {
         match self.kind() {
-            // Look for an impl of both `PartialStructuralEq` and `StructuralEq`.
-            ty::Adt(..) => tcx.has_structural_eq_impls(self),
+            // Look for an impl of `PartialStructuralEq`.
+            ty::Adt(..) => tcx.has_structural_eq_impl(self),
 
             // Primitive types that satisfy `Eq`.
             ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Str | ty::Never => true,

compiler/rustc_mir_build/messages.ftl

@@ -90,7 +90,7 @@ mir_build_extern_static_requires_unsafe_unsafe_op_in_unsafe_fn_allowed =
 mir_build_float_pattern = floating-point types cannot be used in patterns
 
 mir_build_indirect_structural_match =
-    to use a constant of type `{$non_sm_ty}` in a pattern, `{$non_sm_ty}` must be annotated with `#[derive(PartialEq, Eq)]`
+    to use a constant of type `{$non_sm_ty}` in a pattern, `{$non_sm_ty}` must be annotated with `#[derive(PartialEq)]`
 
 mir_build_inform_irrefutable = `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant
 
@@ -230,7 +230,7 @@ mir_build_non_exhaustive_patterns_type_not_empty = non-exhaustive patterns: type
     .help = ensure that all possible cases are being handled by adding a match arm with a wildcard pattern
 
 mir_build_nontrivial_structural_match =
-    to use a constant of type `{$non_sm_ty}` in a pattern, the constant's initializer must be trivial or `{$non_sm_ty}` must be annotated with `#[derive(PartialEq, Eq)]`
+    to use a constant of type `{$non_sm_ty}` in a pattern, the constant's initializer must be trivial or `{$non_sm_ty}` must be annotated with `#[derive(PartialEq)]`
 
 mir_build_overlapping_range_endpoints = multiple patterns overlap on their endpoints
     .range = ... with this range
@@ -277,9 +277,9 @@ mir_build_trailing_irrefutable_let_patterns = trailing irrefutable {$count ->
     } into the body
 
 mir_build_type_not_structural =
-     to use a constant of type `{$non_sm_ty}` in a pattern, `{$non_sm_ty}` must be annotated with `#[derive(PartialEq, Eq)]`
+     to use a constant of type `{$non_sm_ty}` in a pattern, `{$non_sm_ty}` must be annotated with `#[derive(PartialEq)]`
 
-mir_build_type_not_structural_more_info = see https://doc.rust-lang.org/stable/std/marker/trait.StructuralEq.html for details
+mir_build_type_not_structural_more_info = see https://doc.rust-lang.org/stable/std/marker/trait.StructuralPartialEq.html for details
 
 mir_build_type_not_structural_tip = the traits must be derived, manual `impl`s are not sufficient
 

compiler/rustc_span/src/symbol.rs

@@ -286,7 +286,6 @@ symbols! {
         SliceIndex,
         Some,
         String,
-        StructuralEq,
         StructuralPartialEq,
         SubdiagnosticMessage,
         Sync,
@@ -1523,7 +1522,6 @@ symbols! {
         struct_variant,
         structural_match,
         structural_peq,
-        structural_teq,
         sty,
         sub,
         sub_assign,

compiler/rustc_trait_selection/src/traits/structural_match.rs

@@ -39,7 +39,7 @@ pub fn search_for_structural_match_violation<'tcx>(
 
 /// 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`).
+/// `StructuralPartialEq`.
 struct Search<'tcx> {
     span: Span,
 

compiler/rustc_ty_utils/src/structural_match.rs

@@ -6,13 +6,12 @@ use rustc_infer::infer::TyCtxtInferExt;
 use rustc_trait_selection::traits::{ObligationCause, ObligationCtxt};
 
 /// This method returns true if and only if `adt_ty` itself has been marked as
-/// eligible for structural-match: namely, if it implements both
-/// `StructuralPartialEq` and `StructuralEq` (which are respectively injected by
-/// `#[derive(PartialEq)]` and `#[derive(Eq)]`).
+/// eligible for structural-match: namely, if it implements
+/// `StructuralPartialEq` (which is injected by `#[derive(PartialEq)]`).
 ///
 /// Note that this does *not* recursively check if the substructure of `adt_ty`
-/// implements the traits.
-fn has_structural_eq_impls<'tcx>(tcx: TyCtxt<'tcx>, adt_ty: Ty<'tcx>) -> bool {
+/// implements the trait.
+fn has_structural_eq_impl<'tcx>(tcx: TyCtxt<'tcx>, adt_ty: Ty<'tcx>) -> bool {
     let infcx = &tcx.infer_ctxt().build();
     let cause = ObligationCause::dummy();
 
@@ -21,11 +20,6 @@ fn has_structural_eq_impls<'tcx>(tcx: TyCtxt<'tcx>, adt_ty: Ty<'tcx>) -> bool {
     let structural_peq_def_id =
         infcx.tcx.require_lang_item(LangItem::StructuralPeq, Some(cause.span));
     ocx.register_bound(cause.clone(), ty::ParamEnv::empty(), adt_ty, structural_peq_def_id);
-    // 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 structural_teq_def_id =
-        infcx.tcx.require_lang_item(LangItem::StructuralTeq, Some(cause.span));
-    ocx.register_bound(cause, ty::ParamEnv::empty(), adt_ty, structural_teq_def_id);
 
     // We deliberately skip *reporting* fulfillment errors (via
     // `report_fulfillment_errors`), for two reasons:
@@ -40,5 +34,5 @@ fn has_structural_eq_impls<'tcx>(tcx: TyCtxt<'tcx>, adt_ty: Ty<'tcx>) -> bool {
 }
 
 pub fn provide(providers: &mut Providers) {
-    providers.has_structural_eq_impls = has_structural_eq_impls;
+    providers.has_structural_eq_impl = has_structural_eq_impl;
 }

library/core/src/marker.rs

@@ -181,7 +181,7 @@ pub trait Unsize<T: ?Sized> {
 /// Required trait for constants used in pattern matches.
 ///
 /// Any type that derives `PartialEq` automatically implements this trait,
-/// *regardless* of whether its type-parameters implement `Eq`.
+/// *regardless* of whether its type-parameters implement `PartialEq`.
 ///
 /// If a `const` item contains some type that does not implement this trait,
 /// then that type either (1.) does not implement `PartialEq` (which means the
@@ -194,7 +194,7 @@ pub trait Unsize<T: ?Sized> {
 /// a pattern match.
 ///
 /// See also the [structural match RFC][RFC1445], and [issue 63438] which
-/// motivated migrating from attribute-based design to this trait.
+/// motivated migrating from an attribute-based design to this trait.
 ///
 /// [RFC1445]: https://github.com/rust-lang/rfcs/blob/master/text/1445-restrict-constants-in-patterns.md
 /// [issue 63438]: https://github.com/rust-lang/rust/issues/63438
@@ -212,7 +212,7 @@ marker_impls! {
         isize, i8, i16, i32, i64, i128,
         bool,
         char,
-        str /* Technically requires `[u8]: StructuralEq` */,
+        str /* Technically requires `[u8]: StructuralPartialEq` */,
         (),
         {T, const N: usize} [T; N],
         {T} [T],
@@ -268,13 +268,15 @@ marker_impls! {
 #[unstable(feature = "structural_match", issue = "31434")]
 #[rustc_on_unimplemented(message = "the type `{Self}` does not `#[derive(Eq)]`")]
 #[lang = "structural_teq"]
+#[cfg(bootstrap)]
 pub trait StructuralEq {
     // Empty.
 }
 
 // FIXME: Remove special cases of these types from the compiler pattern checking code and always check `T: StructuralEq` instead
 marker_impls! {
     #[unstable(feature = "structural_match", issue = "31434")]
+    #[cfg(bootstrap)]
     StructuralEq for
         usize, u8, u16, u32, u64, u128,
         isize, i8, i16, i32, i64, i128,
@@ -839,6 +841,7 @@ impl<T: ?Sized> Default for PhantomData<T> {
 impl<T: ?Sized> StructuralPartialEq for PhantomData<T> {}
 
 #[unstable(feature = "structural_match", issue = "31434")]
+#[cfg(bootstrap)]
 impl<T: ?Sized> StructuralEq for PhantomData<T> {}
 
 /// Compiler-internal trait used to indicate the type of enum discriminants.
@@ -995,6 +998,20 @@ pub trait PointerLike {}
 #[unstable(feature = "adt_const_params", issue = "95174")]
 #[rustc_on_unimplemented(message = "`{Self}` can't be used as a const parameter type")]
 #[allow(multiple_supertrait_upcastable)]
+#[cfg(not(bootstrap))]
+pub trait ConstParamTy: StructuralPartialEq + Eq {}
+
+/// A marker for types which can be used as types of `const` generic parameters.
+///
+/// These types must have a proper equivalence relation (`Eq`) and it must be automatically
+/// derived (`StructuralPartialEq`). There's a hard-coded check in the compiler ensuring
+/// that all fields are also `ConstParamTy`, which implies that recursively, all fields
+/// are `StructuralPartialEq`.
+#[lang = "const_param_ty"]
+#[unstable(feature = "adt_const_params", issue = "95174")]
+#[rustc_on_unimplemented(message = "`{Self}` can't be used as a const parameter type")]
+#[allow(multiple_supertrait_upcastable)]
+#[cfg(bootstrap)]
 pub trait ConstParamTy: StructuralEq + StructuralPartialEq + Eq {}
 
 /// Derive macro generating an impl of the trait `ConstParamTy`.

library/core/src/tuple.rs

@@ -2,7 +2,7 @@
 
 use crate::cmp::Ordering::{self, *};
 use crate::marker::ConstParamTy;
-use crate::marker::{StructuralEq, StructuralPartialEq};
+use crate::marker::StructuralPartialEq;
 
 // Recursive macro for implementing n-ary tuple functions and operations
 //
@@ -64,7 +64,8 @@ macro_rules! tuple_impls {
         maybe_tuple_doc! {
             $($T)+ @
             #[unstable(feature = "structural_match", issue = "31434")]
-            impl<$($T),+> StructuralEq for ($($T,)+)
+            #[cfg(bootstrap)]
+            impl<$($T),+> crate::marker::StructuralEq for ($($T,)+)
             {}
         }
 

src/tools/clippy/tests/ui/crashes/ice-6254.stderr

@@ -1,4 +1,4 @@
-error: to use a constant of type `Foo` in a pattern, `Foo` must be annotated with `#[derive(PartialEq, Eq)]`
+error: to use a constant of type `Foo` in a pattern, `Foo` must be annotated with `#[derive(PartialEq)]`
   --> $DIR/ice-6254.rs:13:9
    |
 LL |         FOO_REF_REF => {},

tests/ui/const-generics/adt_const_params/const_param_ty_impl_no_structural_eq.rs

@@ -8,13 +8,11 @@ impl std::marker::ConstParamTy for ImplementsConstParamTy {}
 struct CantParam(ImplementsConstParamTy);
 
 impl std::marker::ConstParamTy for CantParam {}
-//~^ error: the type `CantParam` does not `#[derive(Eq)]`
-//~| error: the type `CantParam` does not `#[derive(PartialEq)]`
+//~^ error: the type `CantParam` does not `#[derive(PartialEq)]`
 //~| the trait bound `CantParam: Eq` is not satisfied
 
 #[derive(std::marker::ConstParamTy)]
-//~^ error: the type `CantParamDerive` does not `#[derive(Eq)]`
-//~| error: the type `CantParamDerive` does not `#[derive(PartialEq)]`
+//~^ error: the type `CantParamDerive` does not `#[derive(PartialEq)]`
 //~| the trait bound `CantParamDerive: Eq` is not satisfied
 struct CantParamDerive(ImplementsConstParamTy);
 

tests/ui/const-generics/adt_const_params/const_param_ty_impl_no_structural_eq.stderr

@@ -21,17 +21,8 @@ LL | impl std::marker::ConstParamTy for CantParam {}
 note: required by a bound in `ConstParamTy`
   --> $SRC_DIR/core/src/marker.rs:LL:COL
 
-error[E0277]: the type `CantParam` does not `#[derive(Eq)]`
-  --> $DIR/const_param_ty_impl_no_structural_eq.rs:10:36
-   |
-LL | impl std::marker::ConstParamTy for CantParam {}
-   |                                    ^^^^^^^^^ the trait `StructuralEq` is not implemented for `CantParam`
-   |
-note: required by a bound in `ConstParamTy`
-  --> $SRC_DIR/core/src/marker.rs:LL:COL
-
 error[E0277]: the trait bound `CantParamDerive: Eq` is not satisfied
-  --> $DIR/const_param_ty_impl_no_structural_eq.rs:15:10
+  --> $DIR/const_param_ty_impl_no_structural_eq.rs:14:10
    |
 LL | #[derive(std::marker::ConstParamTy)]
    |          ^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Eq` is not implemented for `CantParamDerive`
@@ -46,7 +37,7 @@ LL | struct CantParamDerive(ImplementsConstParamTy);
    |
 
 error[E0277]: the type `CantParamDerive` does not `#[derive(PartialEq)]`
-  --> $DIR/const_param_ty_impl_no_structural_eq.rs:15:10
+  --> $DIR/const_param_ty_impl_no_structural_eq.rs:14:10
    |
 LL | #[derive(std::marker::ConstParamTy)]
    |          ^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `StructuralPartialEq` is not implemented for `CantParamDerive`
@@ -55,16 +46,6 @@ note: required by a bound in `ConstParamTy`
   --> $SRC_DIR/core/src/marker.rs:LL:COL
    = note: this error originates in the derive macro `std::marker::ConstParamTy` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0277]: the type `CantParamDerive` does not `#[derive(Eq)]`
-  --> $DIR/const_param_ty_impl_no_structural_eq.rs:15:10
-   |
-LL | #[derive(std::marker::ConstParamTy)]
-   |          ^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `StructuralEq` is not implemented for `CantParamDerive`
-   |
-note: required by a bound in `ConstParamTy`
-  --> $SRC_DIR/core/src/marker.rs:LL:COL
-   = note: this error originates in the derive macro `std::marker::ConstParamTy` (in Nightly builds, run with -Z macro-backtrace for more info)
-
-error: aborting due to 6 previous errors
+error: aborting due to 4 previous errors
 
 For more information about this error, try `rustc --explain E0277`.

tests/ui/const-generics/adt_const_params/const_param_ty_impl_union.rs

@@ -1,5 +1,5 @@
 #![allow(incomplete_features)]
-#![feature(adt_const_params, structural_match)]
+#![feature(adt_const_params)]
 
 union Union {
     a: u8,
@@ -11,7 +11,6 @@ impl PartialEq for Union {
     }
 }
 impl Eq for Union {}
-impl std::marker::StructuralEq for Union {}
 
 impl std::marker::ConstParamTy for Union {}
 //~^ ERROR the type `Union` does not `#[derive(PartialEq)]`
@@ -28,7 +27,6 @@ impl PartialEq for UnionDerive {
     }
 }
 impl Eq for UnionDerive {}
-impl std::marker::StructuralEq for UnionDerive {}
 
 
 fn main() {}

tests/ui/const-generics/adt_const_params/const_param_ty_impl_union.stderr

@@ -1,11 +1,11 @@
 error: this trait cannot be derived for unions
-  --> $DIR/const_param_ty_impl_union.rs:19:10
+  --> $DIR/const_param_ty_impl_union.rs:18:10
    |
 LL | #[derive(std::marker::ConstParamTy)]
    |          ^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0277]: the type `Union` does not `#[derive(PartialEq)]`
-  --> $DIR/const_param_ty_impl_union.rs:16:36
+  --> $DIR/const_param_ty_impl_union.rs:15:36
    |
 LL | impl std::marker::ConstParamTy for Union {}
    |                                    ^^^^^ the trait `StructuralPartialEq` is not implemented for `Union`