diff --git a/compiler/rustc_infer/src/infer/combine.rs b/compiler/rustc_infer/src/infer/combine.rs
index bb6fdd2ffc2c9..4503af03ca341 100644
--- a/compiler/rustc_infer/src/infer/combine.rs
+++ b/compiler/rustc_infer/src/infer/combine.rs
@@ -189,10 +189,19 @@ impl<'tcx> InferCtxt<'tcx> {
// the expected const's type. Specifically, we don't want const infer vars
// to do any type shapeshifting before and after resolution.
if let Err(guar) = compatible_types {
- return Ok(self.tcx.const_error_with_guaranteed(
- if relation.a_is_expected() { a.ty() } else { b.ty() },
- guar,
- ));
+ // HACK: equating both sides with `[const error]` eagerly prevents us
+ // from leaving unconstrained inference vars during things like impl
+ // matching in the solver.
+ let a_error = self.tcx.const_error_with_guaranteed(a.ty(), guar);
+ if let ty::ConstKind::Infer(InferConst::Var(vid)) = a.kind() {
+ return self.unify_const_variable(vid, a_error);
+ }
+ let b_error = self.tcx.const_error_with_guaranteed(b.ty(), guar);
+ if let ty::ConstKind::Infer(InferConst::Var(vid)) = b.kind() {
+ return self.unify_const_variable(vid, b_error);
+ }
+
+ return Ok(if relation.a_is_expected() { a_error } else { b_error });
}
match (a.kind(), b.kind()) {
diff --git a/compiler/rustc_trait_selection/src/traits/specialize/mod.rs b/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
index 8e229dd8d6b98..8546bbe52dcc3 100644
--- a/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
+++ b/compiler/rustc_trait_selection/src/traits/specialize/mod.rs
@@ -22,7 +22,7 @@ use crate::traits::{
use rustc_data_structures::fx::FxIndexSet;
use rustc_errors::{error_code, DelayDm, Diagnostic};
use rustc_hir::def_id::{DefId, LocalDefId};
-use rustc_middle::ty::{self, ImplSubject, Ty, TyCtxt};
+use rustc_middle::ty::{self, ImplSubject, Ty, TyCtxt, TypeVisitableExt};
use rustc_middle::ty::{InternalSubsts, SubstsRef};
use rustc_session::lint::builtin::COHERENCE_LEAK_CHECK;
use rustc_session::lint::builtin::ORDER_DEPENDENT_TRAIT_OBJECTS;
@@ -350,6 +350,10 @@ fn report_conflicting_impls<'tcx>(
impl_span: Span,
err: &mut Diagnostic,
) {
+ if (overlap.trait_ref, overlap.self_ty).references_error() {
+ err.downgrade_to_delayed_bug();
+ }
+
match tcx.span_of_impl(overlap.with_impl) {
Ok(span) => {
err.span_label(span, "first implementation here");
diff --git a/tests/ui/const-generics/bad-subst-const-kind.rs b/tests/ui/const-generics/bad-subst-const-kind.rs
new file mode 100644
index 0000000000000..e13dfbacd2422
--- /dev/null
+++ b/tests/ui/const-generics/bad-subst-const-kind.rs
@@ -0,0 +1,13 @@
+// incremental
+#![crate_type = "lib"]
+
+trait Q {
+ const ASSOC: usize;
+}
+
+impl<const N: u64> Q for [u8; N] {
+ //~^ ERROR mismatched types
+ const ASSOC: usize = 1;
+}
+
+pub fn test() -> [u8; <[u8; 13] as Q>::ASSOC] { todo!() }
diff --git a/tests/ui/const-generics/bad-subst-const-kind.stderr b/tests/ui/const-generics/bad-subst-const-kind.stderr
new file mode 100644
index 0000000000000..bd24f9140e4ea
--- /dev/null
+++ b/tests/ui/const-generics/bad-subst-const-kind.stderr
@@ -0,0 +1,9 @@
+error[E0308]: mismatched types
+ --> $DIR/bad-subst-const-kind.rs:8:31
+ |
+LL | impl<const N: u64> Q for [u8; N] {
+ | ^ expected `usize`, found `u64`
+
+error: aborting due to previous error
+
+For more information about this 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 582b480aa25be..5fd7c647c2531 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
@@ -2,11 +2,11 @@
// An impl that has an erroneous const substitution should not specialize one
// that is well-formed.
-
+#[derive(Clone)]
struct S<const L: usize>;
impl<const N: i32> Copy for S<N> {}
+//~^ 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 a3906a9a22fec..6d7028c5e7088 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 +1,14 @@
-error[E0119]: conflicting implementations of trait `Copy` for type `S<_>`
- --> $DIR/bad-const-wf-doesnt-specialize.rs:9:1
+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> {}
- | -------------------------------- first implementation here
-LL | impl<const M: usize> Copy for S<M> {}
- | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `S<_>`
+ | ^^^^
+ |
+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: aborting due to previous error
-For more information about this error, try `rustc --explain E0119`.