Check proj's parent is trait or not when checking dyn compatibility

compiler/rustc_trait_selection/src/traits/dyn_compatibility.rs

@@ -8,6 +8,7 @@ use std::ops::ControlFlow;
 
 use rustc_errors::FatalError;
 use rustc_hir::attrs::AttributeKind;
+use rustc_hir::def::DefKind;
 use rustc_hir::def_id::DefId;
 use rustc_hir::{self as hir, LangItem, find_attr};
 use rustc_middle::query::Providers;
@@ -833,8 +834,10 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for IllegalSelfTypeVisitor<'tcx> {
         match ct.kind() {
             ty::ConstKind::Unevaluated(proj) if self.tcx.features().min_generic_const_args() => {
                 match self.allow_self_projections {
-                    AllowSelfProjections::Yes => {
-                        let trait_def_id = self.tcx.parent(proj.def);
+                    AllowSelfProjections::Yes
+                        if let trait_def_id = self.tcx.parent(proj.def)
+                            && self.tcx.def_kind(trait_def_id) == DefKind::Trait =>
+                    {
                         let trait_ref = ty::TraitRef::from_assoc(self.tcx, trait_def_id, proj.args);
 
                         // Only walk contained consts if the parent trait is not a supertrait.
@@ -844,7 +847,7 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for IllegalSelfTypeVisitor<'tcx> {
                             ct.super_visit_with(self)
                         }
                     }
-                    AllowSelfProjections::No => ct.super_visit_with(self),
+                    _ => ct.super_visit_with(self),
                 }
             }
             _ => ct.super_visit_with(self),

tests/ui/const-generics/mgca/type-const-used-in-trait.rs

@@ -0,0 +1,13 @@
+//@ check-pass
+
+#![feature(min_generic_const_args)]
+#![expect(incomplete_features)]
+
+#[type_const]
+const N: usize = 2;
+
+trait CollectArray<A> {
+    fn inner_array(&mut self) -> [A; N];
+}
+
+fn main() {}