From e388f9eeb2130920f317cade97bfd4d89a2c766e Mon Sep 17 00:00:00 2001
From: Redddy <rust@redddy.com>
Date: Fri, 4 Sep 2026 15:11:26 +0000
Subject: [PATCH] add test for direct-const-arg

---
 .../mgca/direct-const-arg-placeholder.rs      | 10 +++++++++
 .../mgca/direct-const-arg-placeholder.stderr  | 21 +++++++++++++++++++
 2 files changed, 31 insertions(+)
 create mode 100644 tests/ui/const-generics/mgca/direct-const-arg-placeholder.rs
 create mode 100644 tests/ui/const-generics/mgca/direct-const-arg-placeholder.stderr

diff --git a/tests/ui/const-generics/mgca/direct-const-arg-placeholder.rs b/tests/ui/const-generics/mgca/direct-const-arg-placeholder.rs
new file mode 100644
index 0000000000000..72b5221c1fccd
--- /dev/null
+++ b/tests/ui/const-generics/mgca/direct-const-arg-placeholder.rs
@@ -0,0 +1,10 @@
+//! Regression test for <https://github.com/rust-lang/rust/issues/159558>
+#![feature(min_generic_const_args)]
+struct S<const N: usize>;
+
+fn foo() -> S<core::direct_const_arg!(_)> {
+    //~^ ERROR: type annotations needed
+    //~| ERROR: the placeholder `_` is not allowed
+    todo!()
+}
+fn main() {}
diff --git a/tests/ui/const-generics/mgca/direct-const-arg-placeholder.stderr b/tests/ui/const-generics/mgca/direct-const-arg-placeholder.stderr
new file mode 100644
index 0000000000000..1d6b851b009e1
--- /dev/null
+++ b/tests/ui/const-generics/mgca/direct-const-arg-placeholder.stderr
@@ -0,0 +1,21 @@
+error[E0282]: type annotations needed
+  --> $DIR/direct-const-arg-placeholder.rs:5:43
+   |
+LL |   fn foo() -> S<core::direct_const_arg!(_)> {
+   |  ___________________________________________^
+LL | |
+LL | |
+LL | |     todo!()
+LL | | }
+   | |_^ cannot infer type for struct `S<_>`
+
+error[E0121]: the placeholder `_` is not allowed within types on item signatures for return types
+  --> $DIR/direct-const-arg-placeholder.rs:5:39
+   |
+LL | fn foo() -> S<core::direct_const_arg!(_)> {
+   |                                       ^ not allowed in type signatures
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0121, E0282.
+For more information about an error, try `rustc --explain E0121`.