From 0827f765864a17ac6354cc12ff353043cba62286 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Mon, 24 Mar 2025 23:19:33 +0000
Subject: [PATCH] Test define opaques in extern items

---
 .../rustc_builtin_macros/src/define_opaque.rs    |  5 ++++-
 tests/ui/impl-trait/define-via-extern.rs         | 16 ++++++++++++++++
 tests/ui/impl-trait/define-via-extern.stderr     | 14 ++++++++++++++
 3 files changed, 34 insertions(+), 1 deletion(-)
 create mode 100644 tests/ui/impl-trait/define-via-extern.rs
 create mode 100644 tests/ui/impl-trait/define-via-extern.stderr

diff --git a/compiler/rustc_builtin_macros/src/define_opaque.rs b/compiler/rustc_builtin_macros/src/define_opaque.rs
index bd5c48e3d346..cd02e81f5689 100644
--- a/compiler/rustc_builtin_macros/src/define_opaque.rs
+++ b/compiler/rustc_builtin_macros/src/define_opaque.rs
@@ -52,7 +52,10 @@ pub(crate) fn expand(
                 .collect(),
         );
     } else {
-        ecx.dcx().span_err(meta_item.span, "only functions and methods can define opaque types");
+        ecx.dcx().span_err(
+            meta_item.span,
+            "only functions, statics, and consts can define opaque types",
+        );
     }
 
     vec![item]
diff --git a/tests/ui/impl-trait/define-via-extern.rs b/tests/ui/impl-trait/define-via-extern.rs
new file mode 100644
index 000000000000..599c31ff917f
--- /dev/null
+++ b/tests/ui/impl-trait/define-via-extern.rs
@@ -0,0 +1,16 @@
+#![feature(type_alias_impl_trait)]
+
+type Hi = impl Sized;
+
+extern "C" {
+    #[define_opaque(Hi)] fn foo();
+    //~^ ERROR only functions, statics, and consts can define opaque types
+
+    #[define_opaque(Hi)] static HI: Hi;
+    //~^ ERROR only functions, statics, and consts can define opaque types
+}
+
+#[define_opaque(Hi)]
+fn main() {
+    let _: Hi = 0;
+}
diff --git a/tests/ui/impl-trait/define-via-extern.stderr b/tests/ui/impl-trait/define-via-extern.stderr
new file mode 100644
index 000000000000..4a0ca5edd47d
--- /dev/null
+++ b/tests/ui/impl-trait/define-via-extern.stderr
@@ -0,0 +1,14 @@
+error: only functions, statics, and consts can define opaque types
+  --> $DIR/define-via-extern.rs:6:5
+   |
+LL |     #[define_opaque(Hi)] fn foo();
+   |     ^^^^^^^^^^^^^^^^^^^^
+
+error: only functions, statics, and consts can define opaque types
+  --> $DIR/define-via-extern.rs:9:5
+   |
+LL |     #[define_opaque(Hi)] static HI: Hi;
+   |     ^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 2 previous errors
+