1 files changed, 33 insertions, 0 deletions
diff --git a/src/test/ui/regions/regions-lifetime-nonfree-late-bound.rs b/src/test/ui/regions/regions-lifetime-nonfree-late-bound.rs
new file mode 100644
index 000000000..3852a14d9
--- /dev/null
+++ b/src/test/ui/regions/regions-lifetime-nonfree-late-bound.rs
@@ -0,0 +1,33 @@
+// run-pass
+// This is a regression test for the ICE from issue #10846.
+//
+// The original issue causing the ICE: the LUB-computations during
+// type inference were encountering late-bound lifetimes, and
+// asserting that such lifetimes should have already been substituted
+// with a concrete lifetime.
+//
+// However, those encounters were occurring within the lexical scope
+// of the binding for the late-bound lifetime; that is, the late-bound
+// lifetimes were perfectly valid.  The core problem was that the type
+// folding code was over-zealously passing back all lifetimes when
+// doing region-folding, when really all clients of the region-folding
+// case only want to see FREE lifetime variables, not bound ones.
+
+// pretty-expanded FIXME #23616
+
+pub fn main() {
+    fn explicit() {
+        fn test<F>(_x: Option<Box<F>>) where F: FnMut(Box<dyn for<'a> FnMut(&'a isize)>) {}
+        test(Some(Box::new(|_f: Box<dyn for<'a> FnMut(&'a isize)>| {})));
+    }
+
+    // The code below is shorthand for the code above (and more likely
+    // to represent what one encounters in practice).
+    fn implicit() {
+        fn test<F>(_x: Option<Box<F>>) where F: FnMut(Box<dyn        FnMut(&   isize)>) {}
+        test(Some(Box::new(|_f: Box<dyn        FnMut(&   isize)>| {})));
+    }
+
+    explicit();
+    implicit();
+}