1 files changed, 37 insertions, 0 deletions
diff --git a/src/test/ui/unboxed-closures/unboxed-closures-failed-recursive-fn-1.rs b/src/test/ui/unboxed-closures/unboxed-closures-failed-recursive-fn-1.rs
new file mode 100644
index 000000000..1358ba0f9
--- /dev/null
+++ b/src/test/ui/unboxed-closures/unboxed-closures-failed-recursive-fn-1.rs
@@ -0,0 +1,37 @@
+// Various unsuccessful attempts to put the unboxed closure kind
+// inference into an awkward position that might require fixed point
+// iteration (basically where inferring the kind of a closure `c`
+// would require knowing the kind of `c`). I currently believe this is
+// impossible.
+
+fn a() {
+    // This case of recursion wouldn't even require fixed-point
+    // iteration, but it still doesn't work. The weird structure with
+    // the `Option` is to avoid giving any useful hints about the `Fn`
+    // kind via the expected type.
+    let mut factorial: Option<Box<dyn Fn(u32) -> u32>> = None;
+
+    let f = |x: u32| -> u32 {
+        let g = factorial.as_ref().unwrap();
+        //~^ ERROR `factorial` does not live long enough
+        if x == 0 {1} else {x * g(x-1)}
+    };
+
+    factorial = Some(Box::new(f));
+    //~^ ERROR cannot assign to `factorial` because it is borrowed
+}
+
+fn b() {
+    let mut factorial: Option<Box<dyn Fn(u32) -> u32 + 'static>> = None;
+
+    let f = |x: u32| -> u32 {
+        let g = factorial.as_ref().unwrap();
+        //~^ ERROR `factorial` does not live long enough
+        if x == 0 {1} else {x * g(x-1)}
+    };
+
+    factorial = Some(Box::new(f));
+    //~^ ERROR cannot assign to `factorial` because it is borrowed
+}
+
+fn main() { }