1 files changed, 45 insertions, 0 deletions

diff --git a/tests/ui/issues/issue-16739.rs b/tests/ui/issues/issue-16739.rs
new file mode 100644
index 000000000..b21ea4bcd
--- /dev/null
+++ b/tests/ui/issues/issue-16739.rs
@@ -0,0 +1,45 @@
+// run-pass
+#![feature(unboxed_closures, fn_traits)]
+
+// Test that unboxing shim for calling rust-call ABI methods through a
+// trait box works and does not cause an ICE.
+
+struct Foo { foo: u32 }
+
+impl FnMut<()> for Foo {
+    extern "rust-call" fn call_mut(&mut self, _: ()) -> u32 { self.foo }
+}
+
+impl FnOnce<()> for Foo {
+    type Output = u32;
+    extern "rust-call" fn call_once(mut self, _: ()) -> u32 { self.call_mut(()) }
+}
+
+impl FnMut<(u32,)> for Foo {
+    extern "rust-call" fn call_mut(&mut self, (x,): (u32,)) -> u32 { self.foo + x }
+}
+
+impl FnOnce<(u32,)> for Foo {
+    type Output = u32;
+    extern "rust-call" fn call_once(mut self, args: (u32,)) -> u32 { self.call_mut(args) }
+}
+
+impl FnMut<(u32,u32)> for Foo {
+    extern "rust-call" fn call_mut(&mut self, (x, y): (u32, u32)) -> u32 { self.foo + x + y }
+}
+
+impl FnOnce<(u32,u32)> for Foo {
+    type Output = u32;
+    extern "rust-call" fn call_once(mut self, args: (u32,u32)) -> u32 { self.call_mut(args) }
+}
+
+fn main() {
+    let mut f = Box::new(Foo { foo: 42 }) as Box<dyn FnMut() -> u32>;
+    assert_eq!(f.call_mut(()), 42);
+
+    let mut f = Box::new(Foo { foo: 40 }) as Box<dyn FnMut(u32) -> u32>;
+    assert_eq!(f.call_mut((2,)), 42);
+
+    let mut f = Box::new(Foo { foo: 40 }) as Box<dyn FnMut(u32, u32) -> u32>;
+    assert_eq!(f.call_mut((1, 1)), 42);
+}