Add Self: ~const Trait to traits with #[const_trait]

compiler/rustc_const_eval/src/transform/check_consts/ops.rs

@@ -23,8 +23,8 @@ use rustc_trait_selection::traits::SelectionContext;
 
 use super::ConstCx;
 use crate::errors::{
-    MutDerefErr, NonConstOpErr, PanicNonStrErr, RawPtrComparisonErr, RawPtrToIntErr,
-    StaticAccessErr, TransientMutBorrowErr, TransientMutBorrowErrRaw,
+    MutDerefErr, NonConstOpErr, PanicNonStrErr, RawPtrToIntErr, StaticAccessErr,
+    TransientMutBorrowErr, TransientMutBorrowErrRaw,
 };
 use crate::util::{call_kind, CallDesugaringKind, CallKind};
 
@@ -654,10 +654,10 @@ pub struct RawPtrComparison;
 impl<'tcx> NonConstOp<'tcx> for RawPtrComparison {
     fn build_error(
         &self,
-        ccx: &ConstCx<'_, 'tcx>,
+        _: &ConstCx<'_, 'tcx>,
         span: Span,
     ) -> DiagnosticBuilder<'tcx, ErrorGuaranteed> {
-        ccx.tcx.sess.create_err(RawPtrComparisonErr { span })
+        span_bug!(span, "raw ptr comparison should already be caught in the trait system");
     }
 }
 

compiler/rustc_middle/src/ty/mod.rs

@@ -829,6 +829,14 @@ impl<'tcx> TraitPredicate<'tcx> {
     pub fn is_const_if_const(self) -> bool {
         self.constness == BoundConstness::ConstIfConst
     }
+
+    pub fn is_constness_satisfied_by(self, constness: hir::Constness) -> bool {
+        match (self.constness, constness) {
+            (BoundConstness::NotConst, _)
+            | (BoundConstness::ConstIfConst, hir::Constness::Const) => true,
+            (BoundConstness::ConstIfConst, hir::Constness::NotConst) => false,
+        }
+    }
 }
 
 impl<'tcx> PolyTraitPredicate<'tcx> {

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -2556,7 +2556,7 @@ define_print_and_forward_display! {
 
     ty::TraitPredicate<'tcx> {
         p!(print(self.trait_ref.self_ty()), ": ");
-        if let ty::BoundConstness::ConstIfConst = self.constness {
+        if let ty::BoundConstness::ConstIfConst = self.constness && cx.tcx().features().const_trait_impl {
             p!("~const ");
         }
         p!(print(self.trait_ref.print_only_trait_path()))

compiler/rustc_trait_selection/src/traits/error_reporting/mod.rs

@@ -666,7 +666,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                             );
                         } else if !suggested {
                             // Can't show anything else useful, try to find similar impls.
-                            let impl_candidates = self.find_similar_impl_candidates(trait_ref);
+                            let impl_candidates = self.find_similar_impl_candidates(trait_predicate);
                             if !self.report_similar_impl_candidates(
                                 impl_candidates,
                                 trait_ref,
@@ -701,7 +701,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
                                 {
                                     let trait_ref = trait_pred.to_poly_trait_ref();
                                     let impl_candidates =
-                                        self.find_similar_impl_candidates(trait_ref);
+                                        self.find_similar_impl_candidates(trait_pred);
                                     self.report_similar_impl_candidates(
                                         impl_candidates,
                                         trait_ref,
@@ -1325,7 +1325,7 @@ trait InferCtxtPrivExt<'hir, 'tcx> {
 
     fn find_similar_impl_candidates(
         &self,
-        trait_ref: ty::PolyTraitRef<'tcx>,
+        trait_pred: ty::PolyTraitPredicate<'tcx>,
     ) -> Vec<ImplCandidate<'tcx>>;
 
     fn report_similar_impl_candidates(
@@ -1694,18 +1694,22 @@ impl<'a, 'tcx> InferCtxtPrivExt<'a, 'tcx> for InferCtxt<'a, 'tcx> {
 
     fn find_similar_impl_candidates(
         &self,
-        trait_ref: ty::PolyTraitRef<'tcx>,
+        trait_pred: ty::PolyTraitPredicate<'tcx>,
     ) -> Vec<ImplCandidate<'tcx>> {
         self.tcx
-            .all_impls(trait_ref.def_id())
+            .all_impls(trait_pred.def_id())
             .filter_map(|def_id| {
-                if self.tcx.impl_polarity(def_id) == ty::ImplPolarity::Negative {
+                if self.tcx.impl_polarity(def_id) == ty::ImplPolarity::Negative
+                    || !trait_pred
+                        .skip_binder()
+                        .is_constness_satisfied_by(self.tcx.constness(def_id))
+                {
                     return None;
                 }
 
                 let imp = self.tcx.impl_trait_ref(def_id).unwrap();
 
-                self.fuzzy_match_tys(trait_ref.skip_binder().self_ty(), imp.self_ty(), false)
+                self.fuzzy_match_tys(trait_pred.skip_binder().self_ty(), imp.self_ty(), false)
                     .map(|similarity| ImplCandidate { trait_ref: imp, similarity })
             })
             .collect()

compiler/rustc_typeck/src/collect.rs

@@ -2090,10 +2090,17 @@ fn predicates_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::GenericPredicates<'_> {
         // from the trait itself that *shouldn't* be shown as the source of
         // an obligation and instead be skipped. Otherwise we'd use
         // `tcx.def_span(def_id);`
+
+        let constness = if tcx.has_attr(def_id, sym::const_trait) {
+            ty::BoundConstness::ConstIfConst
+        } else {
+            ty::BoundConstness::NotConst
+        };
+
         let span = rustc_span::DUMMY_SP;
         result.predicates =
             tcx.arena.alloc_from_iter(result.predicates.iter().copied().chain(std::iter::once((
-                ty::TraitRef::identity(tcx, def_id).without_const().to_predicate(tcx),
+                ty::TraitRef::identity(tcx, def_id).with_constness(constness).to_predicate(tcx),
                 span,
             ))));
     }

library/core/src/cmp.rs

@@ -1503,9 +1503,10 @@ mod impls {
     // & pointers
 
     #[stable(feature = "rust1", since = "1.0.0")]
-    impl<A: ?Sized, B: ?Sized> PartialEq<&B> for &A
+    #[rustc_const_unstable(feature = "const_cmp", issue = "92391")]
+    impl<A: ?Sized, B: ?Sized> const PartialEq<&B> for &A
     where
-        A: PartialEq<B>,
+        A: ~const PartialEq<B>,
     {
         #[inline]
         fn eq(&self, other: &&B) -> bool {

src/test/ui/const-generics/issues/issue-90318.rs

@@ -12,16 +12,14 @@ impl True for If<true> {}
 fn consume<T: 'static>(_val: T)
 where
     If<{ TypeId::of::<T>() != TypeId::of::<()>() }>: True,
-    //~^ ERROR: overly complex generic constant
-    //~| ERROR: cannot call non-const operator in constants
+    //~^ ERROR: can't compare
 {
 }
 
 fn test<T: 'static>()
 where
     If<{ TypeId::of::<T>() != TypeId::of::<()>() }>: True,
-    //~^ ERROR: overly complex generic constant
-    //~| ERROR: cannot call non-const operator in constants
+    //~^ ERROR: can't compare
 {
 }
 

src/test/ui/const-generics/issues/issue-90318.stderr

@@ -1,53 +1,29 @@
-error: overly complex generic constant
-  --> $DIR/issue-90318.rs:14:8
+error[E0277]: can't compare `TypeId` with `_` in const contexts
+  --> $DIR/issue-90318.rs:14:28
    |
 LL |     If<{ TypeId::of::<T>() != TypeId::of::<()>() }>: True,
-   |        ^^-----------------^^^^^^^^^^^^^^^^^^^^^^^^
-   |          |
-   |          borrowing is not supported in generic constants
+   |                            ^^ no implementation for `TypeId == _`
    |
-   = help: consider moving this anonymous constant into a `const` function
-   = note: this operation may be supported in the future
-
-error[E0015]: cannot call non-const operator in constants
-  --> $DIR/issue-90318.rs:14:10
+   = help: the trait `~const PartialEq<_>` is not implemented for `TypeId`
+note: the trait `PartialEq<_>` is implemented for `TypeId`, but that implementation is not `const`
+  --> $DIR/issue-90318.rs:14:28
    |
 LL |     If<{ TypeId::of::<T>() != TypeId::of::<()>() }>: True,
-   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-note: impl defined here, but it is not `const`
-  --> $SRC_DIR/core/src/any.rs:LL:COL
-   |
-LL | #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)]
-   |                       ^^^^^^^^^
-   = note: calls in constants are limited to constant functions, tuple structs and tuple variants
-   = note: this error originates in the derive macro `PartialEq` (in Nightly builds, run with -Z macro-backtrace for more info)
+   |                            ^^
 
-error: overly complex generic constant
-  --> $DIR/issue-90318.rs:22:8
+error[E0277]: can't compare `TypeId` with `_` in const contexts
+  --> $DIR/issue-90318.rs:21:28
    |
 LL |     If<{ TypeId::of::<T>() != TypeId::of::<()>() }>: True,
-   |        ^^-----------------^^^^^^^^^^^^^^^^^^^^^^^^
-   |          |
-   |          borrowing is not supported in generic constants
+   |                            ^^ no implementation for `TypeId == _`
    |
-   = help: consider moving this anonymous constant into a `const` function
-   = note: this operation may be supported in the future
-
-error[E0015]: cannot call non-const operator in constants
-  --> $DIR/issue-90318.rs:22:10
+   = help: the trait `~const PartialEq<_>` is not implemented for `TypeId`
+note: the trait `PartialEq<_>` is implemented for `TypeId`, but that implementation is not `const`
+  --> $DIR/issue-90318.rs:21:28
    |
 LL |     If<{ TypeId::of::<T>() != TypeId::of::<()>() }>: True,
-   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-note: impl defined here, but it is not `const`
-  --> $SRC_DIR/core/src/any.rs:LL:COL
-   |
-LL | #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)]
-   |                       ^^^^^^^^^
-   = note: calls in constants are limited to constant functions, tuple structs and tuple variants
-   = note: this error originates in the derive macro `PartialEq` (in Nightly builds, run with -Z macro-backtrace for more info)
+   |                            ^^
 
-error: aborting due to 4 previous errors
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0015`.
+For more information about this error, try `rustc --explain E0277`.

src/test/ui/consts/const-eval/const_raw_ptr_ops.rs

@@ -1,6 +1,6 @@
 fn main() {}
 
 // unconst and bad, will thus error in miri
-const X: bool = unsafe { &1 as *const i32 == &2 as *const i32 }; //~ ERROR cannot be reliably
+const X: bool = unsafe { &1 as *const i32 == &2 as *const i32 }; //~ ERROR can't compare
 // unconst and bad, will thus error in miri
-const X2: bool = unsafe { 42 as *const i32 == 43 as *const i32 }; //~ ERROR cannot be reliably
+const X2: bool = unsafe { 42 as *const i32 == 43 as *const i32 }; //~ ERROR can't compare

src/test/ui/consts/const-eval/const_raw_ptr_ops.stderr

@@ -1,18 +1,49 @@
-error: pointers cannot be reliably compared during const eval
-  --> $DIR/const_raw_ptr_ops.rs:4:26
+error[E0277]: can't compare `*const i32` with `_` in const contexts
+  --> $DIR/const_raw_ptr_ops.rs:4:43
    |
 LL | const X: bool = unsafe { &1 as *const i32 == &2 as *const i32 };
-   |                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                           ^^ no implementation for `*const i32 == _`
    |
-   = note: see issue #53020 <https://github.com/rust-lang/rust/issues/53020> for more information
+   = help: the trait `~const PartialEq<_>` is not implemented for `*const i32`
+note: the trait `PartialEq<_>` is implemented for `*const i32`, but that implementation is not `const`
+  --> $DIR/const_raw_ptr_ops.rs:4:43
+   |
+LL | const X: bool = unsafe { &1 as *const i32 == &2 as *const i32 };
+   |                                           ^^
+   = help: the following other types implement trait `PartialEq<Rhs>`:
+             f32
+             f64
+             i128
+             i16
+             i32
+             i64
+             i8
+             isize
+           and 6 others
 
-error: pointers cannot be reliably compared during const eval
-  --> $DIR/const_raw_ptr_ops.rs:6:27
+error[E0277]: can't compare `*const i32` with `_` in const contexts
+  --> $DIR/const_raw_ptr_ops.rs:6:44
    |
 LL | const X2: bool = unsafe { 42 as *const i32 == 43 as *const i32 };
-   |                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                            ^^ no implementation for `*const i32 == _`
    |
-   = note: see issue #53020 <https://github.com/rust-lang/rust/issues/53020> for more information
+   = help: the trait `~const PartialEq<_>` is not implemented for `*const i32`
+note: the trait `PartialEq<_>` is implemented for `*const i32`, but that implementation is not `const`
+  --> $DIR/const_raw_ptr_ops.rs:6:44
+   |
+LL | const X2: bool = unsafe { 42 as *const i32 == 43 as *const i32 };
+   |                                            ^^
+   = help: the following other types implement trait `PartialEq<Rhs>`:
+             f32
+             f64
+             i128
+             i16
+             i32
+             i64
+             i8
+             isize
+           and 6 others
 
 error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0277`.

src/test/ui/consts/issue-25826.rs

@@ -1,6 +1,6 @@
 fn id<T>(t: T) -> T { t }
 fn main() {
     const A: bool = unsafe { id::<u8> as *const () < id::<u16> as *const () };
-    //~^ ERROR pointers cannot be reliably compared during const eval
+    //~^ ERROR can't compare
     println!("{}", A);
 }

src/test/ui/consts/issue-25826.stderr

@@ -1,10 +1,20 @@
-error: pointers cannot be reliably compared during const eval
-  --> $DIR/issue-25826.rs:3:30
+error[E0277]: can't compare `*const ()` with `*const ()` in const contexts
+  --> $DIR/issue-25826.rs:3:52
    |
 LL |     const A: bool = unsafe { id::<u8> as *const () < id::<u16> as *const () };
-   |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                                                    ^ no implementation for `*const () < *const ()` and `*const () > *const ()`
    |
-   = note: see issue #53020 <https://github.com/rust-lang/rust/issues/53020> for more information
+   = help: the trait `~const PartialOrd` is not implemented for `*const ()`
+note: the trait `PartialOrd` is implemented for `*const ()`, but that implementation is not `const`
+  --> $DIR/issue-25826.rs:3:52
+   |
+LL |     const A: bool = unsafe { id::<u8> as *const () < id::<u16> as *const () };
+   |                                                    ^
+help: consider introducing a `where` clause, but there might be an alternative better way to express this requirement
+   |
+LL | fn main() where *const (): ~const PartialOrd {
+   |           ++++++++++++++++++++++++++++++++++
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0277`.

src/test/ui/consts/min_const_fn/cmp_fn_pointers.rs

@@ -1,6 +1,6 @@
 const fn cmp(x: fn(), y: fn()) -> bool {
     unsafe { x == y }
-    //~^ ERROR pointers cannot be reliably compared
+    //~^ ERROR can't compare
 }
 
 fn main() {}

src/test/ui/consts/min_const_fn/cmp_fn_pointers.stderr

@@ -1,10 +1,16 @@
-error: pointers cannot be reliably compared during const eval
-  --> $DIR/cmp_fn_pointers.rs:2:14
+error[E0277]: can't compare `fn()` with `_` in const contexts
+  --> $DIR/cmp_fn_pointers.rs:2:16
    |
 LL |     unsafe { x == y }
-   |              ^^^^^^
+   |                ^^ no implementation for `fn() == _`
    |
-   = note: see issue #53020 <https://github.com/rust-lang/rust/issues/53020> for more information
+   = help: the trait `~const PartialEq<_>` is not implemented for `fn()`
+note: the trait `PartialEq<_>` is implemented for `fn()`, but that implementation is not `const`
+  --> $DIR/cmp_fn_pointers.rs:2:16
+   |
+LL |     unsafe { x == y }
+   |                ^^
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0277`.

src/test/ui/consts/miri_unleashed/ptr_arith.rs

@@ -2,14 +2,8 @@
 #![feature(core_intrinsics)]
 #![allow(const_err)]
 
-// During CTFE, we prevent pointer comparison and pointer-to-int casts.
-
-static CMP: () = {
-    let x = &0 as *const _;
-    let _v = x == x;
-    //~^ ERROR could not evaluate static initializer
-    //~| "pointer arithmetic or comparison" needs an rfc before being allowed inside constants
-};
+// During CTFE, we prevent pointer-to-int casts.
+// Pointer comparisons are prevented in the trait system.
 
 static PTR_INT_CAST: () = {
     let x = &0 as *const _ as usize;