Layout of `&dyn Trait<[type error]>` is still wide

2 files changed, 22 insertions, 0 deletions

diff --git a/tests/ui/layout/transmute-to-tail-with-err.rs b/tests/ui/layout/transmute-to-tail-with-err.rs
new file mode 100644
index 00000000000..6753ce15ed1
--- /dev/null
+++ b/tests/ui/layout/transmute-to-tail-with-err.rs
@@ -0,0 +1,8 @@
+trait Trait<T> {}
+
+struct Bar(Box<dyn Trait<T>>);
+//~^ ERROR cannot find type `T` in this scope
+
+fn main() {
+    let x: Bar = unsafe { std::mem::transmute(()) };
+}
diff --git a/tests/ui/layout/transmute-to-tail-with-err.stderr b/tests/ui/layout/transmute-to-tail-with-err.stderr
new file mode 100644
index 00000000000..97ab59c398a
--- /dev/null
+++ b/tests/ui/layout/transmute-to-tail-with-err.stderr
@@ -0,0 +1,14 @@
+error[E0412]: cannot find type `T` in this scope
+  --> $DIR/transmute-to-tail-with-err.rs:3:26
+   |
+LL | struct Bar(Box<dyn Trait<T>>);
+   |                          ^ not found in this scope
+   |
+help: you might be missing a type parameter
+   |
+LL | struct Bar<T>(Box<dyn Trait<T>>);
+   |           +++
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0412`.