miri: lift restriction on extern types being the only field in a struct

1 files changed, 58 insertions, 0 deletions

diff --git a/src/test/ui/consts/const-eval/issue-91827-extern-types.rs b/src/test/ui/consts/const-eval/issue-91827-extern-types.rs
new file mode 100644
index 00000000000..d5576ebfd02
--- /dev/null
+++ b/src/test/ui/consts/const-eval/issue-91827-extern-types.rs
@@ -0,0 +1,58 @@
+// run-pass
+//
+// Test that we can handle unsized types with an extern type tail part.
+// Regression test for issue #91827.
+
+#![feature(const_ptr_offset_from)]
+#![feature(const_slice_from_raw_parts)]
+#![feature(extern_types)]
+
+use std::ptr::addr_of;
+
+extern "C" {
+    type Opaque;
+}
+
+unsafe impl Sync for Opaque {}
+
+#[repr(C)]
+pub struct List<T> {
+    len: usize,
+    data: [T; 0],
+    tail: Opaque,
+}
+
+#[repr(C)]
+pub struct ListImpl<T, const N: usize> {
+    len: usize,
+    data: [T; N],
+}
+
+impl<T> List<T> {
+    const fn as_slice(&self) -> &[T] {
+        unsafe { std::slice::from_raw_parts(self.data.as_ptr(), self.len) }
+    }
+}
+
+impl<T, const N: usize> ListImpl<T, N> {
+    const fn as_list(&self) -> &List<T> {
+        unsafe { std::mem::transmute(self) }
+    }
+}
+
+pub static A: ListImpl<u128, 3> = ListImpl {
+    len: 3,
+    data: [5, 6, 7],
+};
+pub static A_REF: &'static List<u128> = A.as_list();
+pub static A_TAIL_OFFSET: isize = tail_offset(A.as_list());
+
+const fn tail_offset<T>(list: &List<T>) -> isize {
+    unsafe { (addr_of!(list.tail) as *const u8).offset_from(list as *const List<T> as *const u8) }
+}
+
+fn main() {
+    assert_eq!(A_REF.as_slice(), &[5, 6, 7]);
+    // Check that interpreter and code generation agree about the position of the tail field.
+    assert_eq!(A_TAIL_OFFSET, tail_offset(A_REF));
+}