Rollup merge of #125451 - oli-obk:const_type_mismatch, r=compiler-errors

Fail relating constants of different types

fixes #121585
fixes #121858
fixes #124151

I gave this several attempts before, but we lost too many important diagnostics until I managed to make compilation never bail out early. We have reached this point, so now we can finally fix all those ICEs by bubbling up an error instead of continueing when we encounter a bug.

21 files changed, 129 insertions, 180 deletions

diff --git a/compiler/rustc_infer/src/infer/relate/combine.rs b/compiler/rustc_infer/src/infer/relate/combine.rs
index 101598c5951..7e7d4f43c7c 100644
--- a/compiler/rustc_infer/src/infer/relate/combine.rs
+++ b/compiler/rustc_infer/src/infer/relate/combine.rs
@@ -22,11 +22,11 @@ use super::glb::Glb;
 use super::lub::Lub;
 use super::type_relating::TypeRelating;
 use super::StructurallyRelateAliases;
-use crate::infer::{DefineOpaqueTypes, InferCtxt, TypeTrace};
+use crate::infer::{DefineOpaqueTypes, InferCtxt, InferOk, TypeTrace};
 use crate::traits::{Obligation, PredicateObligations};
 use rustc_middle::bug;
-use rustc_middle::infer::canonical::OriginalQueryValues;
 use rustc_middle::infer::unify_key::EffectVarValue;
+use rustc_middle::traits::ObligationCause;
 use rustc_middle::ty::error::{ExpectedFound, TypeError};
 use rustc_middle::ty::relate::{RelateResult, TypeRelation};
 use rustc_middle::ty::{self, InferConst, Ty, TyCtxt, TypeVisitableExt, Upcast};
@@ -159,36 +159,11 @@ impl<'tcx> InferCtxt<'tcx> {
         let a = self.shallow_resolve_const(a);
         let b = self.shallow_resolve_const(b);
 
-        // We should never have to relate the `ty` field on `Const` as it is checked elsewhere that consts have the
-        // correct type for the generic param they are an argument for. However there have been a number of cases
-        // historically where asserting that the types are equal has found bugs in the compiler so this is valuable
-        // to check even if it is a bit nasty impl wise :(
-        //
-        // This probe is probably not strictly necessary but it seems better to be safe and not accidentally find
-        // ourselves with a check to find bugs being required for code to compile because it made inference progress.
-        self.probe(|_| {
-            if a.ty() == b.ty() {
-                return;
-            }
-
-            // We don't have access to trait solving machinery in `rustc_infer` so the logic for determining if the
-            // two const param's types are able to be equal has to go through a canonical query with the actual logic
-            // in `rustc_trait_selection`.
-            let canonical = self.canonicalize_query(
-                relation.param_env().and((a.ty(), b.ty())),
-                &mut OriginalQueryValues::default(),
-            );
-            self.tcx.check_tys_might_be_eq(canonical).unwrap_or_else(|_| {
-                // The error will only be reported later. If we emit an ErrorGuaranteed
-                // here, then we will never get to the code that actually emits the error.
-                self.tcx.dcx().delayed_bug(format!(
-                    "cannot relate consts of different types (a={a:?}, b={b:?})",
-                ));
-                // We treat these constants as if they were of the same type, so that any
-                // such constants being used in impls make these impls match barring other mismatches.
-                // This helps with diagnostics down the road.
-            });
-        });
+        // It is always an error if the types of two constants that are related are not equal.
+        let InferOk { value: (), obligations } = self
+            .at(&ObligationCause::dummy_with_span(relation.span()), relation.param_env())
+            .eq(DefineOpaqueTypes::No, a.ty(), b.ty())?;
+        relation.register_obligations(obligations);
 
         match (a.kind(), b.kind()) {
             (
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 5a6decc4f94..8ca7a465c2a 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -2218,15 +2218,6 @@ rustc_queries! {
         separate_provide_extern
     }
 
-    /// Used in `super_combine_consts` to ICE if the type of the two consts are definitely not going to end up being
-    /// equal to eachother. This might return `Ok` even if the types are not equal, but will never return `Err` if
-    /// the types might be equal.
-    query check_tys_might_be_eq(
-        arg: Canonical<'tcx, ty::ParamEnvAnd<'tcx, (Ty<'tcx>, Ty<'tcx>)>>
-    ) -> Result<(), NoSolution> {
-        desc { "check whether two const param are definitely not equal to eachother"}
-    }
-
     /// Get all item paths that were stripped by a `#[cfg]` in a particular crate.
     /// Should not be called for the local crate before the resolver outputs are created, as it
     /// is only fed there.
diff --git a/compiler/rustc_trait_selection/src/traits/misc.rs b/compiler/rustc_trait_selection/src/traits/misc.rs
index da2b004761f..a1094d98276 100644
--- a/compiler/rustc_trait_selection/src/traits/misc.rs
+++ b/compiler/rustc_trait_selection/src/traits/misc.rs
@@ -1,17 +1,14 @@
 //! Miscellaneous type-system utilities that are too small to deserve their own modules.
 
 use crate::regions::InferCtxtRegionExt;
-use crate::traits::{self, ObligationCause, ObligationCtxt};
+use crate::traits::{self, ObligationCause};
 
 use hir::LangItem;
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir as hir;
-use rustc_infer::infer::canonical::Canonical;
 use rustc_infer::infer::{RegionResolutionError, TyCtxtInferExt};
-use rustc_infer::traits::query::NoSolution;
 use rustc_infer::{infer::outlives::env::OutlivesEnvironment, traits::FulfillmentError};
 use rustc_middle::ty::{self, AdtDef, Ty, TyCtxt, TypeVisitableExt};
-use rustc_span::DUMMY_SP;
 
 use super::outlives_bounds::InferCtxtExt;
 
@@ -207,19 +204,3 @@ pub fn all_fields_implement_trait<'tcx>(
 
     if infringing.is_empty() { Ok(()) } else { Err(infringing) }
 }
-
-pub fn check_tys_might_be_eq<'tcx>(
-    tcx: TyCtxt<'tcx>,
-    canonical: Canonical<'tcx, ty::ParamEnvAnd<'tcx, (Ty<'tcx>, Ty<'tcx>)>>,
-) -> Result<(), NoSolution> {
-    let (infcx, key, _) = tcx.infer_ctxt().build_with_canonical(DUMMY_SP, &canonical);
-    let (param_env, (ty_a, ty_b)) = key.into_parts();
-    let ocx = ObligationCtxt::new(&infcx);
-
-    let result = ocx.eq(&ObligationCause::dummy(), param_env, ty_a, ty_b);
-    // use `select_where_possible` instead of `select_all_or_error` so that
-    // we don't get errors from obligations being ambiguous.
-    let errors = ocx.select_where_possible();
-
-    if errors.len() > 0 || result.is_err() { Err(NoSolution) } else { Ok(()) }
-}
diff --git a/compiler/rustc_trait_selection/src/traits/mod.rs b/compiler/rustc_trait_selection/src/traits/mod.rs
index 204bb487c86..f6003a25028 100644
--- a/compiler/rustc_trait_selection/src/traits/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/mod.rs
@@ -551,7 +551,6 @@ pub fn provide(providers: &mut Providers) {
         specialization_graph_of: specialize::specialization_graph_provider,
         specializes: specialize::specializes,
         instantiate_and_check_impossible_predicates,
-        check_tys_might_be_eq: misc::check_tys_might_be_eq,
         is_impossible_associated_item,
         ..*providers
     };
diff --git a/tests/crashes/119381.rs b/tests/crashes/119381.rs
deleted file mode 100644
index 51d1d084ba2..00000000000
--- a/tests/crashes/119381.rs
+++ /dev/null
@@ -1,6 +0,0 @@
-//@ known-bug: #119381
-
-#![feature(with_negative_coherence)]
-trait Trait {}
-impl<const N: u8> Trait for [(); N] {}
-impl<const N: i8> Trait for [(); N] {}
diff --git a/tests/crashes/121585-1.rs b/tests/crashes/121585-1.rs
deleted file mode 100644
index 2a4638efcab..00000000000
--- a/tests/crashes/121585-1.rs
+++ /dev/null
@@ -1,13 +0,0 @@
-//@ known-bug: #121585
-#![feature(generic_const_exprs)]
-
-trait Trait {}
-
-struct HasCastInTraitImpl<const N: usize, const M: u128>;
-impl<const O: f64> Trait for HasCastInTraitImpl<O, { O as u128 }> {}
-
-pub fn use_trait_impl() {
-    fn assert_impl<T: Trait>() {}
-
-    assert_impl::<HasCastInTraitImpl<13, 13>>();
-}
diff --git a/tests/crashes/121585-2.rs b/tests/crashes/121585-2.rs
deleted file mode 100644
index 99cc8f79195..00000000000
--- a/tests/crashes/121585-2.rs
+++ /dev/null
@@ -1,30 +0,0 @@
-//@ known-bug: #121585
-//@ check-pass
-#![feature(generic_const_exprs)]
-#![allow(incomplete_features)]
-
-trait Trait {}
-pub struct EvaluatableU128<const N: u128>;
-
-struct HasCastInTraitImpl<const N: usize, const M: u128>;
-impl<const O: f64> Trait for HasCastInTraitImpl<O, { O as u128 }> {}
-
-pub fn use_trait_impl<const N: usize>() where EvaluatableU128<{N as u128}>:, {
-    fn assert_impl<T: Trait>() {}
-
-    assert_impl::<HasCastInTraitImpl<N, { N as u128 }>>();
-    assert_impl::<HasCastInTraitImpl<N, { N as _ }>>();
-    assert_impl::<HasCastInTraitImpl<12, { 12 as u128 }>>();
-    assert_impl::<HasCastInTraitImpl<13, 13>>();
-}
-pub fn use_trait_impl_2<const N: usize>() where EvaluatableU128<{N as _}>:, {
-    fn assert_impl<T: Trait>() {}
-
-    assert_impl::<HasCastInTraitImpl<N, { N as u128 }>>();
-    assert_impl::<HasCastInTraitImpl<N, { N as _ }>>();
-    assert_impl::<HasCastInTraitImpl<12, { 12 as u128 }>>()const NUM: u8 = xyz();
-    assert_impl::<HasCastInTraitImpl<13, 13>>();
-}
-
-
-fn main() {}
diff --git a/tests/crashes/121858-2.rs b/tests/crashes/121858-2.rs
deleted file mode 100644
index cb80c081cff..00000000000
--- a/tests/crashes/121858-2.rs
+++ /dev/null
@@ -1,20 +0,0 @@
-//@ known-bug: #121858
-#![allow(named_arguments_used_positionally)]
-#![feature(generic_const_exprs)]
-struct Inner<const N: usize, const M: usize>;
-impl<const N: usize, const M: usize> Inner<N, M> where [(); N + M]: {
-    fn i() -> Self {
-        Self
-    }
-}
-
-struct Outer<const A: i64, const B: usize>(Inner<A, { B * 2 }>) where [(); A + (B * 2)]:;
-impl<const A: usize, const B: usize> Outer<A, B> where [(); A + (B * 2)]: {
-    fn o() -> Union {
-        Self(Inner::i())
-    }
-}
-
-fn main() {
-    Outer::<1, 1>::o();
-}
diff --git a/tests/crashes/124151.rs b/tests/crashes/124151.rs
deleted file mode 100644
index 5e55ac2aa94..00000000000
--- a/tests/crashes/124151.rs
+++ /dev/null
@@ -1,14 +0,0 @@
-//@ known-bug: #124151
-#![feature(generic_const_exprs)]
-
-use std::ops::Add;
-
-pub struct Dimension;
-
-pub struct Quantity<S, const D: Dimension>(S);
-
-impl<const D: Dimension, LHS, RHS> Add<LHS, D> for Quantity<LHS, { Dimension }> {}
-
-pub fn add<const U: Dimension>(x: Quantity<f32, U>) -> Quantity<f32, U> {
-    x + y
-}
diff --git a/tests/ui/coherence/negative-coherence/generic_const_type_mismatch.rs b/tests/ui/coherence/negative-coherence/generic_const_type_mismatch.rs
new file mode 100644
index 00000000000..89d0b74d403
--- /dev/null
+++ b/tests/ui/coherence/negative-coherence/generic_const_type_mismatch.rs
@@ -0,0 +1,12 @@
+//! This test used to ICE (#119381), because relating the `u8` and `i8` generic
+//! const with the array length of the `Self` type was succeeding under the
+//! assumption that an error had already been reported.
+
+#![feature(with_negative_coherence)]
+trait Trait {}
+impl<const N: u8> Trait for [(); N] {}
+//~^ ERROR: mismatched types
+impl<const N: i8> Trait for [(); N] {}
+//~^ ERROR: mismatched types
+
+fn main() {}
diff --git a/tests/ui/coherence/negative-coherence/generic_const_type_mismatch.stderr b/tests/ui/coherence/negative-coherence/generic_const_type_mismatch.stderr
new file mode 100644
index 00000000000..d1950254660
--- /dev/null
+++ b/tests/ui/coherence/negative-coherence/generic_const_type_mismatch.stderr
@@ -0,0 +1,15 @@
+error[E0308]: mismatched types
+  --> $DIR/generic_const_type_mismatch.rs:7:34
+   |
+LL | impl<const N: u8> Trait for [(); N] {}
+   |                                  ^ expected `usize`, found `u8`
+
+error[E0308]: mismatched types
+  --> $DIR/generic_const_type_mismatch.rs:9:34
+   |
+LL | impl<const N: i8> Trait for [(); N] {}
+   |                                  ^ expected `usize`, found `i8`
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0308`.
diff --git a/tests/ui/const-generics/bad-subst-const-kind.rs b/tests/ui/const-generics/bad-subst-const-kind.rs
index ca5522a2ddf..88f98a54b6e 100644
--- a/tests/ui/const-generics/bad-subst-const-kind.rs
+++ b/tests/ui/const-generics/bad-subst-const-kind.rs
@@ -11,4 +11,4 @@ impl<const N: u64> Q for [u8; N] {
 }
 
 pub fn test() -> [u8; <[u8; 13] as Q>::ASSOC] { todo!() }
-//~^ ERROR: the constant `13` is not of type `u64`
+//~^ ERROR: `[u8; 13]: Q` is not satisfied
diff --git a/tests/ui/const-generics/bad-subst-const-kind.stderr b/tests/ui/const-generics/bad-subst-const-kind.stderr
index c04a05573be..6cf9fa743b3 100644
--- a/tests/ui/const-generics/bad-subst-const-kind.stderr
+++ b/tests/ui/const-generics/bad-subst-const-kind.stderr
@@ -1,16 +1,10 @@
-error: the constant `13` is not of type `u64`
+error[E0277]: the trait bound `[u8; 13]: Q` is not satisfied
   --> $DIR/bad-subst-const-kind.rs:13:24
    |
 LL | pub fn test() -> [u8; <[u8; 13] as Q>::ASSOC] { todo!() }
-   |                        ^^^^^^^^ expected `u64`, found `usize`
+   |                        ^^^^^^^^ the trait `Q` is not implemented for `[u8; 13]`
    |
-note: required for `[u8; 13]` to implement `Q`
-  --> $DIR/bad-subst-const-kind.rs:8:20
-   |
-LL | impl<const N: u64> Q for [u8; N] {
-   |      ------------  ^     ^^^^^^^
-   |      |
-   |      unsatisfied trait bound introduced here
+   = help: the trait `Q` is implemented for `[u8; N]`
 
 error[E0308]: mismatched types
   --> $DIR/bad-subst-const-kind.rs:8:31
@@ -20,4 +14,5 @@ LL | impl<const N: u64> Q for [u8; N] {
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0308`.
+Some errors have detailed explanations: E0277, E0308.
+For more information about an error, try `rustc --explain E0277`.
diff --git a/tests/ui/const-generics/generic_const_exprs/type_mismatch.rs b/tests/ui/const-generics/generic_const_exprs/type_mismatch.rs
index 6b0d9e047db..285f9dee6c2 100644
--- a/tests/ui/const-generics/generic_const_exprs/type_mismatch.rs
+++ b/tests/ui/const-generics/generic_const_exprs/type_mismatch.rs
@@ -10,7 +10,7 @@ impl<const N: u64> Q for [u8; N] {}
 //~| ERROR mismatched types
 
 pub fn q_user() -> [u8; <[u8; 13] as Q>::ASSOC] {}
-//~^ ERROR the constant `13` is not of type `u64`
+//~^ ERROR `[u8; 13]: Q` is not satisfied
 //~| ERROR mismatched types
 
 pub fn main() {}
diff --git a/tests/ui/const-generics/generic_const_exprs/type_mismatch.stderr b/tests/ui/const-generics/generic_const_exprs/type_mismatch.stderr
index bb6d650b7ab..a63a56dd675 100644
--- a/tests/ui/const-generics/generic_const_exprs/type_mismatch.stderr
+++ b/tests/ui/const-generics/generic_const_exprs/type_mismatch.stderr
@@ -7,19 +7,13 @@ LL |     const ASSOC: usize;
 LL | impl<const N: u64> Q for [u8; N] {}
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing `ASSOC` in implementation
 
-error: the constant `13` is not of type `u64`
+error[E0277]: the trait bound `[u8; 13]: Q` is not satisfied
   --> $DIR/type_mismatch.rs:12:26
    |
 LL | pub fn q_user() -> [u8; <[u8; 13] as Q>::ASSOC] {}
-   |                          ^^^^^^^^ expected `u64`, found `usize`
+   |                          ^^^^^^^^ the trait `Q` is not implemented for `[u8; 13]`
    |
-note: required for `[u8; 13]` to implement `Q`
-  --> $DIR/type_mismatch.rs:8:20
-   |
-LL | impl<const N: u64> Q for [u8; N] {}
-   |      ------------  ^     ^^^^^^^
-   |      |
-   |      unsatisfied trait bound introduced here
+   = help: the trait `Q` is implemented for `[u8; N]`
 
 error[E0308]: mismatched types
   --> $DIR/type_mismatch.rs:12:20
@@ -37,5 +31,5 @@ LL | impl<const N: u64> Q for [u8; N] {}
 
 error: aborting due to 4 previous errors
 
-Some errors have detailed explanations: E0046, E0308.
+Some errors have detailed explanations: E0046, E0277, E0308.
 For more information about an error, try `rustc --explain E0046`.
diff --git a/tests/ui/const-generics/issues/issue-105821.rs b/tests/ui/const-generics/issues/issue-105821.rs
index a0a98103b2c..282cbe9249d 100644
--- a/tests/ui/const-generics/issues/issue-105821.rs
+++ b/tests/ui/const-generics/issues/issue-105821.rs
@@ -1,4 +1,10 @@
-//@ check-pass
+//@ failure-status: 101
+//@ known-bug: unknown
+//@ normalize-stderr-test "note: .*\n\n" -> ""
+//@ normalize-stderr-test "thread 'rustc' panicked.*\n.*\n" -> ""
+//@ normalize-stderr-test "(error: internal compiler error: [^:]+):\d+:\d+: " -> "$1:LL:CC: "
+//@ normalize-stderr-test "delayed at .*" -> ""
+//@ rustc-env:RUST_BACKTRACE=0
 
 #![allow(incomplete_features)]
 #![feature(adt_const_params, generic_const_exprs)]
diff --git a/tests/ui/const-generics/issues/issue-105821.stderr b/tests/ui/const-generics/issues/issue-105821.stderr
new file mode 100644
index 00000000000..1f0fc0f33ce
--- /dev/null
+++ b/tests/ui/const-generics/issues/issue-105821.stderr
@@ -0,0 +1,8 @@
+error: internal compiler error: compiler/rustc_borrowck/src/universal_regions.rs:LL:CC: cannot convert `'{erased}` to a region vid
+
+query stack during panic:
+#0 [mir_borrowck] borrow-checking `<impl at $DIR/issue-105821.rs:21:1: 23:24>::R`
+#1 [analysis] running analysis passes on this crate
+end of query stack
+error: aborting due to 1 previous error
+
diff --git a/tests/crashes/121858.rs b/tests/ui/consts/eval_type_mismatch.rs
index 7d5bae37f84..3d821ab538e 100644
--- a/tests/crashes/121858.rs
+++ b/tests/ui/consts/eval_type_mismatch.rs
@@ -1,14 +1,17 @@
-//@ known-bug: #121858
 #![feature(generic_const_exprs)]
+#![allow(incomplete_features)]
 
 struct Outer<const A: i64, const B: usize>();
 impl<const A: usize, const B: usize> Outer<A, B>
+//~^ ERROR: `A` is not of type `i64`
+//~| ERROR: mismatched types
 where
     [(); A + (B * 2)]:,
 {
-    fn o() -> Union {}
+    fn o() {}
 }
 
 fn main() {
     Outer::<1, 1>::o();
+    //~^ ERROR: no function or associated item named `o` found
 }
diff --git a/tests/ui/consts/eval_type_mismatch.stderr b/tests/ui/consts/eval_type_mismatch.stderr
new file mode 100644
index 00000000000..38d6e33d406
--- /dev/null
+++ b/tests/ui/consts/eval_type_mismatch.stderr
@@ -0,0 +1,34 @@
+error: the constant `A` is not of type `i64`
+  --> $DIR/eval_type_mismatch.rs:5:38
+   |
+LL | impl<const A: usize, const B: usize> Outer<A, B>
+   |                                      ^^^^^^^^^^^ expected `i64`, found `usize`
+   |
+note: required by a bound in `Outer`
+  --> $DIR/eval_type_mismatch.rs:4:14
+   |
+LL | struct Outer<const A: i64, const B: usize>();
+   |              ^^^^^^^^^^^^ required by this bound in `Outer`
+
+error[E0599]: no function or associated item named `o` found for struct `Outer<1, 1>` in the current scope
+  --> $DIR/eval_type_mismatch.rs:15:20
+   |
+LL | struct Outer<const A: i64, const B: usize>();
+   | ------------------------------------------ function or associated item `o` not found for this struct
+...
+LL |     Outer::<1, 1>::o();
+   |                    ^ function or associated item not found in `Outer<1, 1>`
+   |
+   = note: the function or associated item was found for
+           - `Outer<A, B>`
+
+error[E0308]: mismatched types
+  --> $DIR/eval_type_mismatch.rs:5:44
+   |
+LL | impl<const A: usize, const B: usize> Outer<A, B>
+   |                                            ^ expected `i64`, found `usize`
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0308, E0599.
+For more information about an error, try `rustc --explain E0308`.
diff --git a/tests/ui/specialization/min_specialization/bad-const-wf-doesnt-specialize.rs b/tests/ui/specialization/min_specialization/bad-const-wf-doesnt-specialize.rs
index f89a463bc58..4d1cd4332fe 100644
--- a/tests/ui/specialization/min_specialization/bad-const-wf-doesnt-specialize.rs
+++ b/tests/ui/specialization/min_specialization/bad-const-wf-doesnt-specialize.rs
@@ -7,7 +7,8 @@ struct S<const L: usize>;
 
 impl<const N: i32> Copy for S<N> {}
 //~^ ERROR: mismatched types
+//~| ERROR: the trait bound `S<N>: Clone` is not satisfied
+//~| ERROR: the constant `N` is not of type `usize`
 impl<const M: usize> Copy for S<M> {}
-//~^ ERROR: conflicting implementations of trait `Copy` for type `S<_>`
 
 fn main() {}
diff --git a/tests/ui/specialization/min_specialization/bad-const-wf-doesnt-specialize.stderr b/tests/ui/specialization/min_specialization/bad-const-wf-doesnt-specialize.stderr
index 1dac58e1f69..716a4787948 100644
--- a/tests/ui/specialization/min_specialization/bad-const-wf-doesnt-specialize.stderr
+++ b/tests/ui/specialization/min_specialization/bad-const-wf-doesnt-specialize.stderr
@@ -1,11 +1,29 @@
-error[E0119]: conflicting implementations of trait `Copy` for type `S<_>`
-  --> $DIR/bad-const-wf-doesnt-specialize.rs:10:1
+error[E0277]: the trait bound `S<N>: Clone` is not satisfied
+  --> $DIR/bad-const-wf-doesnt-specialize.rs:8:29
    |
 LL | impl<const N: i32> Copy for S<N> {}
-   | -------------------------------- first implementation here
-LL |
-LL | impl<const M: usize> Copy for S<M> {}
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `S<_>`
+   |                             ^^^^ the trait `Clone` is not implemented for `S<N>`
+   |
+   = help: the trait `Clone` is implemented for `S<L>`
+note: required by a bound in `Copy`
+  --> $SRC_DIR/core/src/marker.rs:LL:COL
+help: consider annotating `S<N>` with `#[derive(Clone)]`
+   |
+LL + #[derive(Clone)]
+LL | struct S<const L: usize>;
+   |
+
+error: the constant `N` is not of type `usize`
+  --> $DIR/bad-const-wf-doesnt-specialize.rs:8:29
+   |
+LL | impl<const N: i32> Copy for S<N> {}
+   |                             ^^^^ expected `usize`, found `i32`
+   |
+note: required by a bound in `S`
+  --> $DIR/bad-const-wf-doesnt-specialize.rs:6:10
+   |
+LL | struct S<const L: usize>;
+   |          ^^^^^^^^^^^^^^ required by this bound in `S`
 
 error[E0308]: mismatched types
   --> $DIR/bad-const-wf-doesnt-specialize.rs:8:31
@@ -13,7 +31,7 @@ error[E0308]: mismatched types
 LL | impl<const N: i32> Copy for S<N> {}
    |                               ^ expected `usize`, found `i32`
 
-error: aborting due to 2 previous errors
+error: aborting due to 3 previous errors
 
-Some errors have detailed explanations: E0119, E0308.
-For more information about an error, try `rustc --explain E0119`.
+Some errors have detailed explanations: E0277, E0308.
+For more information about an error, try `rustc --explain E0277`.