From 64d98f8ee037282c35007b64c2649055c56af1db Mon Sep 17 00:00:00 2001
From: Daniel Baumann <daniel.baumann@progress-linux.org>
Date: Wed, 17 Apr 2024 14:19:03 +0200
Subject: Merging upstream version 1.68.2+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
---
 .../issue-84660-unsoundness.rs                     | 41 ++++++++++++++++++++++
 1 file changed, 41 insertions(+)
 create mode 100644 tests/ui/type-alias-impl-trait/issue-84660-unsoundness.rs

(limited to 'tests/ui/type-alias-impl-trait/issue-84660-unsoundness.rs')

diff --git a/tests/ui/type-alias-impl-trait/issue-84660-unsoundness.rs b/tests/ui/type-alias-impl-trait/issue-84660-unsoundness.rs
new file mode 100644
index 000000000..48d4b0c96
--- /dev/null
+++ b/tests/ui/type-alias-impl-trait/issue-84660-unsoundness.rs
@@ -0,0 +1,41 @@
+// Another example from issue #84660, this time weaponized as a safe transmute: an opaque type in an
+// impl header being accepted was used to create unsoundness.
+
+#![feature(type_alias_impl_trait)]
+
+trait Foo {}
+impl Foo for () {}
+type Bar = impl Foo;
+fn _defining_use() -> Bar {}
+
+trait Trait<T, In> {
+    type Out;
+    fn convert(i: In) -> Self::Out;
+}
+
+impl<In, Out> Trait<Bar, In> for Out {
+    type Out = Out;
+    fn convert(_i: In) -> Self::Out {
+        unreachable!();
+    }
+}
+
+impl<In, Out> Trait<(), In> for Out { //~ ERROR conflicting implementations of trait `Trait<Bar, _>`
+    type Out = In;
+    fn convert(i: In) -> Self::Out {
+        i
+    }
+}
+
+fn transmute<In, Out>(i: In) -> Out {
+    <Out as Trait<Bar, In>>::convert(i)
+}
+
+fn main() {
+    let d;
+    {
+        let x = "Hello World".to_string();
+        d = transmute::<&String, &String>(&x);
+    }
+    println!("{}", d);
+}
-- 
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