Fix - const parameters rejected when identical

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -85,7 +85,7 @@ fn check_method_is_structurally_compatible<'tcx>(
 ) -> Result<(), ErrorGuaranteed> {
     compare_self_type(tcx, impl_m, trait_m, impl_trait_ref, delay)?;
     compare_number_of_generics(tcx, impl_m, trait_m, delay)?;
-    compare_generic_param_kinds(tcx, impl_m, trait_m, delay)?;
+    compare_generic_param_kinds(tcx, impl_m, trait_m, impl_trait_ref, delay)?;
     compare_number_of_method_arguments(tcx, impl_m, trait_m, delay)?;
     compare_synthetic_generics(tcx, impl_m, trait_m, delay)?;
     check_region_bounds_on_impl_item(tcx, impl_m, trait_m, delay)?;
@@ -2063,6 +2063,7 @@ fn compare_generic_param_kinds<'tcx>(
     tcx: TyCtxt<'tcx>,
     impl_item: ty::AssocItem,
     trait_item: ty::AssocItem,
+    impl_trait_ref: ty::TraitRef<'tcx>,
     delay: bool,
 ) -> Result<(), ErrorGuaranteed> {
     assert_eq!(impl_item.tag(), trait_item.tag());
@@ -2076,6 +2077,18 @@ fn compare_generic_param_kinds<'tcx>(
         })
     };
 
+    // Map the trait item's generic parameters into the impl item's generic context.
+    let trait_to_impl_args = ty::GenericArgs::identity_for_item(tcx, impl_item.def_id).rebase_onto(
+        tcx,
+        impl_item.container_id(tcx),
+        impl_trait_ref.args,
+    );
+
+    let const_param_tys_match = |param_impl_def_id, param_trait_def_id| {
+        tcx.type_of(param_impl_def_id).instantiate_identity().skip_norm_wip()
+            == tcx.type_of(param_trait_def_id).instantiate(tcx, trait_to_impl_args).skip_norm_wip()
+    };
+
     for (param_impl, param_trait) in
         iter::zip(ty_const_params_of(impl_item.def_id), ty_const_params_of(trait_item.def_id))
     {
@@ -2084,7 +2097,8 @@ fn compare_generic_param_kinds<'tcx>(
             (Const { .. }, Const { .. })
                 if tcx.type_of(param_impl.def_id) != tcx.type_of(param_trait.def_id) =>
             {
-                true
+                // Do a more thorough check
+                !const_param_tys_match(param_impl.def_id, param_trait.def_id)
             }
             (Const { .. }, Type { .. }) | (Type { .. }, Const { .. }) => true,
             // this is exhaustive so that anyone adding new generic param kinds knows
@@ -2146,7 +2160,7 @@ fn compare_impl_const<'tcx>(
 ) -> Result<(), ErrorGuaranteed> {
     compare_const_directness(tcx, impl_const_item, trait_const_item)?;
     compare_number_of_generics(tcx, impl_const_item, trait_const_item, false)?;
-    compare_generic_param_kinds(tcx, impl_const_item, trait_const_item, false)?;
+    compare_generic_param_kinds(tcx, impl_const_item, trait_const_item, impl_trait_ref, false)?;
     check_region_bounds_on_impl_item(tcx, impl_const_item, trait_const_item, false)?;
     compare_const_clause_entailment(tcx, impl_const_item, trait_const_item, impl_trait_ref)
 }
@@ -2324,7 +2338,7 @@ fn compare_impl_ty<'tcx>(
     impl_trait_ref: ty::TraitRef<'tcx>,
 ) -> Result<(), ErrorGuaranteed> {
     compare_number_of_generics(tcx, impl_ty, trait_ty, false)?;
-    compare_generic_param_kinds(tcx, impl_ty, trait_ty, false)?;
+    compare_generic_param_kinds(tcx, impl_ty, trait_ty, impl_trait_ref, false)?;
     check_region_bounds_on_impl_item(tcx, impl_ty, trait_ty, false)?;
     compare_type_clause_entailment(tcx, impl_ty, trait_ty, impl_trait_ref)?;
     check_type_bounds(tcx, trait_ty, impl_ty, impl_trait_ref)

tests/ui/const-generics/method-instantiation.rs

@@ -0,0 +1,16 @@
+//@ compile-flags: --crate-type lib
+//@ check-pass
+
+#![feature(min_adt_const_params)]
+#![feature(generic_const_parameter_types)]
+#![allow(incomplete_features)]
+
+pub trait Trait {
+    fn method<const A: usize, const B: [usize; A]>();
+}
+
+pub struct Foo;
+
+impl Trait for Foo {
+    fn method<const A: usize, const B: [usize; A]>() {}
+}