1 files changed, 26 insertions, 0 deletions
diff --git a/src/test/ui/nll/issue-57843.rs b/src/test/ui/nll/issue-57843.rs
new file mode 100644
index 000000000..11629690e
--- /dev/null
+++ b/src/test/ui/nll/issue-57843.rs
@@ -0,0 +1,26 @@
+// Regression test for an ICE that occurred with the universes code:
+//
+// The signature of the closure `|_|` was being inferred to
+// `exists<'r> fn(&'r u8)`. This should result in a type error since
+// the signature `for<'r> fn(&'r u8)` is required. However, due to a
+// bug in the type variable generalization code, the placeholder for
+// `'r` was leaking out into the writeback phase, causing an ICE.
+
+trait ClonableFn<T> {
+    fn clone(&self) -> Box<dyn Fn(T)>;
+}
+
+impl<T, F: 'static> ClonableFn<T> for F
+where
+    F: Fn(T) + Clone,
+{
+    fn clone(&self) -> Box<dyn Fn(T)> {
+        Box::new(self.clone())
+    }
+}
+
+struct Foo(Box<dyn for<'a> ClonableFn<&'a bool>>);
+
+fn main() {
+    Foo(Box::new(|_| ())); //~ ERROR implementation of `FnOnce` is not general enough
+}