Auto merge of rust-lang#116167 - RalfJung:structural-eq, r=lcnr

remove StructuralEq trait

The documentation given for the trait is outdated: *all* function pointers implement `PartialEq` and `Eq` these days. So the `StructuralEq` trait doesn't really seem to have any reason to exist any more.

One side-effect of this PR is that we allow matching on some consts that do not implement `Eq`. However, we already allowed matching on floats and consts containing floats, so this is not new, it is just allowed in more cases now. IMO it makes no sense at all to allow float matching but also sometimes require an `Eq` instance. If we want to require `Eq` we should adjust rust-lang#115893 to check for `Eq`, and rule out float matching for good.

Fixes rust-lang#115881

Author: bors

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

@@ -61,9 +61,6 @@ 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

@@ -138,7 +138,7 @@ 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

@@ -1360,9 +1360,9 @@ 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 `StructuralPartialEq`",
             ty
         }
     }

compiler/rustc_middle/src/ty/util.rs

@@ -1249,19 +1249,18 @@ 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 `StructuralPartialEq` 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 `StructuralPartialEq`.
+            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

@@ -110,7 +110,7 @@ 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
 
@@ -254,7 +254,7 @@ mir_build_non_partial_eq_match =
     to use a constant of type `{$non_peq_ty}` in a pattern, the type must implement `PartialEq`
 
 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_pattern_not_covered = refutable pattern in {$origin}
     .pattern_ty = the matched value is of type `{$pattern_ty}`
@@ -297,9 +297,9 @@ 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

@@ -310,7 +310,6 @@ symbols! {
         Some,
         SpanCtxt,
         String,
-        StructuralEq,
         StructuralPartialEq,
         SubdiagnosticMessage,
         Sync,
@@ -1625,7 +1624,6 @@ symbols! {
         struct_variant,
         structural_match,
         structural_peq,
-        structural_teq,
         sub,
         sub_assign,
         sub_with_overflow,