Lower hir::ConstArgKind::Array to a ValTree

Author: reddevilmidzy

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -2383,15 +2383,30 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             hir::ConstArgKind::TupleCall(qpath, args) => {
                 self.lower_const_arg_tuple_call(hir_id, qpath, args, const_arg.span())
             }
-            hir::ConstArgKind::Array(_array_expr) => {
-                span_bug!(const_arg.span(), "lowering `{:?}` is not yet implemented", const_arg)
-            }
+            hir::ConstArgKind::Array(array_expr) => self.lower_const_arg_array(array_expr),
             hir::ConstArgKind::Anon(anon) => self.lower_const_arg_anon(anon),
             hir::ConstArgKind::Infer(span, ()) => self.ct_infer(None, span),
             hir::ConstArgKind::Error(_, e) => ty::Const::new_error(tcx, e),
         }
     }
 
+    fn lower_const_arg_array(&self, array_expr: &'tcx hir::ConstArgArrayExpr<'tcx>) -> Const<'tcx> {
+        let tcx = self.tcx();
+
+        let array_len = array_expr.elems.len() as u64;
+        let elem_ty = self.ty_infer(None, array_expr.span);
+        let elems = array_expr
+            .elems
+            .iter()
+            .map(|elem| self.lower_const_arg(elem, FeedConstTy::No))
+            .collect::<Vec<_>>();
+
+        let array_ty = Ty::new_array(tcx, elem_ty, array_len);
+        let valtree = ty::ValTree::from_branches(tcx, elems);
+
+        ty::Const::new_value(tcx, valtree, array_ty)
+    }
+
     fn lower_const_arg_tuple_call(
         &self,
         hir_id: HirId,

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

@@ -0,0 +1,19 @@
+#![expect(incomplete_features)]
+#![feature(min_generic_const_args, adt_const_params)]
+
+fn takes_array<const A: [u32; 3]>() {}
+
+fn generic_caller<const N: u32, const N2: u32>() {
+    takes_array::<{ [N, N2, N] }>(); // ok
+
+    takes_array::<{ [N, N2, 1] }>(); // not implemented
+    //~^ ERROR complex const arguments must be placed inside of a `const` block
+
+    takes_array::<{ [N, N2, 1 + 1] }>(); // not implemented
+    //~^ ERROR complex const arguments must be placed inside of a `const` block
+
+    takes_array::<{ [N; 3] }>(); // not implemented
+    //~^ ERROR complex const arguments must be placed inside of a `const` block
+}
+
+fn main() {}

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

@@ -0,0 +1,20 @@
+error: complex const arguments must be placed inside of a `const` block
+  --> $DIR/array-expr.rs:9:29
+   |
+LL |     takes_array::<{ [N, N2, 1] }>(); // not implemented
+   |                             ^
+
+error: complex const arguments must be placed inside of a `const` block
+  --> $DIR/array-expr.rs:12:29
+   |
+LL |     takes_array::<{ [N, N2, 1 + 1] }>(); // not implemented
+   |                             ^^^^^
+
+error: complex const arguments must be placed inside of a `const` block
+  --> $DIR/array-expr.rs:15:19
+   |
+LL |     takes_array::<{ [N; 3] }>(); // not implemented
+   |                   ^^^^^^^^^^
+
+error: aborting due to 3 previous errors
+