1 files changed, 26 insertions, 0 deletions
diff --git a/src/test/ui/functions-closures/closure-expected-type/supply-just-return-type.rs b/src/test/ui/functions-closures/closure-expected-type/supply-just-return-type.rs
new file mode 100644
index 000000000..e9964531c
--- /dev/null
+++ b/src/test/ui/functions-closures/closure-expected-type/supply-just-return-type.rs
@@ -0,0 +1,26 @@
+// run-pass
+fn with_closure<F, R>(f: F) -> Result<char, R>
+    where F: FnOnce(&char) -> Result<char, R>,
+{
+    f(&'a')
+}
+
+fn main() {
+    // Test that supplying the `-> Result<char, ()>` manually here
+    // (which is needed to constrain `R`) still allows us to figure
+    // out that the type of `x` is `&'a char` where `'a` is bound in
+    // the closure (if we didn't, we'd get a type-error because
+    // `with_closure` requires a bound region).
+    //
+    // This pattern was found in the wild.
+    let z = with_closure(|x| -> Result<char, ()> { Ok(*x) });
+    assert_eq!(z.unwrap(), 'a');
+
+    // It also works with `_`:
+    let z = with_closure(|x: _| -> Result<char, ()> { Ok(*x) });
+    assert_eq!(z.unwrap(), 'a');
+
+    // It also works with `&_`:
+    let z = with_closure(|x: &_| -> Result<char, ()> { Ok(*x) });
+    assert_eq!(z.unwrap(), 'a');
+}