1 files changed, 18 insertions, 0 deletions

diff --git a/src/test/ui/issues/issue-23966.stderr b/src/test/ui/issues/issue-23966.stderr
new file mode 100644
index 000000000..ae8233d5c
--- /dev/null
+++ b/src/test/ui/issues/issue-23966.stderr
@@ -0,0 +1,18 @@
+error[E0277]: expected a `FnMut<(_, char)>` closure, found `()`
+  --> $DIR/issue-23966.rs:2:32
+   |
+LL |     "".chars().fold(|_, _| (), ());
+   |                ----            ^^ expected an `FnMut<(_, char)>` closure, found `()`
+   |                |
+   |                required by a bound introduced by this call
+   |
+   = help: the trait `FnMut<(_, char)>` is not implemented for `()`
+note: required by a bound in `fold`
+  --> $SRC_DIR/core/src/iter/traits/iterator.rs:LL:COL
+   |
+LL |         F: FnMut(B, Self::Item) -> B,
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `fold`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0277`.