From 698f8c2f01ea549d77d7dc3338a12e04c11057b9 Mon Sep 17 00:00:00 2001
From: Daniel Baumann <daniel.baumann@progress-linux.org>
Date: Wed, 17 Apr 2024 14:02:58 +0200
Subject: Adding upstream version 1.64.0+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
---
 .../unboxed-closures-infer-recursive-fn.rs         | 45 ++++++++++++++++++++++
 1 file changed, 45 insertions(+)
 create mode 100644 src/test/ui/unboxed-closures/unboxed-closures-infer-recursive-fn.rs

(limited to 'src/test/ui/unboxed-closures/unboxed-closures-infer-recursive-fn.rs')

diff --git a/src/test/ui/unboxed-closures/unboxed-closures-infer-recursive-fn.rs b/src/test/ui/unboxed-closures/unboxed-closures-infer-recursive-fn.rs
new file mode 100644
index 000000000..a0fbbafe2
--- /dev/null
+++ b/src/test/ui/unboxed-closures/unboxed-closures-infer-recursive-fn.rs
@@ -0,0 +1,45 @@
+// run-pass
+#![feature(fn_traits, unboxed_closures)]
+
+use std::marker::PhantomData;
+
+// Test that we are able to infer a suitable kind for a "recursive"
+// closure.  As far as I can tell, coding up a recursive closure
+// requires the good ol' [Y Combinator].
+//
+// [Y Combinator]: https://en.wikipedia.org/wiki/Fixed-point_combinator#Y_combinator
+
+struct YCombinator<F,A,R> {
+    func: F,
+    marker: PhantomData<(A,R)>,
+}
+
+impl<F,A,R> YCombinator<F,A,R> {
+    fn new(f: F) -> YCombinator<F,A,R> {
+        YCombinator { func: f, marker: PhantomData }
+    }
+}
+
+impl<A,R,F : Fn(&dyn Fn(A) -> R, A) -> R> Fn<(A,)> for YCombinator<F,A,R> {
+    extern "rust-call" fn call(&self, (arg,): (A,)) -> R {
+        (self.func)(self, arg)
+    }
+}
+
+impl<A,R,F : Fn(&dyn Fn(A) -> R, A) -> R> FnMut<(A,)> for YCombinator<F,A,R> {
+    extern "rust-call" fn call_mut(&mut self, args: (A,)) -> R { self.call(args) }
+}
+
+impl<A,R,F : Fn(&dyn Fn(A) -> R, A) -> R> FnOnce<(A,)> for YCombinator<F,A,R> {
+    type Output = R;
+    extern "rust-call" fn call_once(self, args: (A,)) -> R { self.call(args) }
+}
+
+fn main() {
+    let factorial = |recur: &dyn Fn(u32) -> u32, arg: u32| -> u32 {
+        if arg == 0 {1} else {arg * recur(arg-1)}
+    };
+    let factorial: YCombinator<_,u32,u32> = YCombinator::new(factorial);
+    let r = factorial(10);
+    assert_eq!(3628800, r);
+}
-- 
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