mgca: Type-check field of array expr const args

compiler/rustc_trait_selection/src/traits/wf.rs

@@ -1094,6 +1094,23 @@ impl<'a, 'tcx> TypeVisitor<TyCtxt<'tcx>> for WfPredicates<'a, 'tcx> {
                                 },
                             ));
                         }
+                        ty::Array(elem_ty, _len) => {
+                            let field_vals = val.to_branch();
+                            let cause = self.cause(ObligationCauseCode::WellFormed(None));
+
+                            self.out.extend(field_vals.iter().map(|&field_val| {
+                                let predicate = ty::PredicateKind::Clause(
+                                    ty::ClauseKind::ConstArgHasType(field_val, *elem_ty),
+                                );
+                                traits::Obligation::with_depth(
+                                    tcx,
+                                    cause.clone(),
+                                    self.recursion_depth,
+                                    self.param_env,
+                                    predicate,
+                                )
+                            }));
+                        }
                         _ => {}
                     }
                 }

tests/ui/const-generics/mgca/array-expr-type-missmatch.rs

@@ -0,0 +1,15 @@
+#![expect(incomplete_features)]
+#![feature(min_generic_const_args, adt_const_params)]
+
+use std::marker::ConstParamTy;
+
+#[derive(Eq, PartialEq, ConstParamTy)]
+struct Foo;
+struct Bar;
+
+fn takes_array<const A: [Foo; 1]>() {}
+
+fn main() {
+    takes_array::<{ [Bar] }>();
+    //~^ ERROR: the constant `Bar` is not of type `Foo`
+}

tests/ui/const-generics/mgca/array-expr-type-missmatch.stderr

@@ -0,0 +1,8 @@
+error: the constant `Bar` is not of type `Foo`
+  --> $DIR/array-expr-type-missmatch.rs:13:21
+   |
+LL |     takes_array::<{ [Bar] }>();
+   |                     ^^^^^ expected `Foo`, found `Bar`
+
+error: aborting due to 1 previous error
+