1 files changed, 22 insertions, 0 deletions

diff --git a/src/test/ui/issues/issue-20971.rs b/src/test/ui/issues/issue-20971.rs
new file mode 100644
index 00000000000..4fb901e2272
--- /dev/null
+++ b/src/test/ui/issues/issue-20971.rs
@@ -0,0 +1,22 @@
+// Regression test for Issue #20971.
+
+// run-fail
+// error-pattern:Hello, world!
+
+pub trait Parser {
+    type Input;
+    fn parse(&mut self, input: <Self as Parser>::Input);
+}
+
+impl Parser for () {
+    type Input = ();
+    fn parse(&mut self, input: ()) {}
+}
+
+pub fn many() -> Box<dyn Parser<Input = <() as Parser>::Input> + 'static> {
+    panic!("Hello, world!")
+}
+
+fn main() {
+    many().parse(());
+}