From 99d9f97a443b53cd275e4fa444c60dd6a76e7193 Mon Sep 17 00:00:00 2001
From: Nicholas Matsakis <nmatsakis@psyche.localdomain>
Date: Wed, 11 Dec 2019 10:09:40 -0500
Subject: [PATCH] Add regression test for #66757

---
 .../never-value-fallback-issue-66757.rs       | 29 +++++++++++++++++++
 1 file changed, 29 insertions(+)
 create mode 100644 src/test/ui/never_type/never-value-fallback-issue-66757.rs

diff --git a/src/test/ui/never_type/never-value-fallback-issue-66757.rs b/src/test/ui/never_type/never-value-fallback-issue-66757.rs
new file mode 100644
index 0000000000000..f2e9e087307db
--- /dev/null
+++ b/src/test/ui/never_type/never-value-fallback-issue-66757.rs
@@ -0,0 +1,29 @@
+// Regression test for #66757
+//
+// Test than when you have a `!` value (e.g., the local variable
+// never) and an uninferred variable (here the argument to `From`) it
+// doesn't fallback to `()` but rather `!`.
+//
+// run-pass
+
+#![feature(never_type)]
+
+// FIXME(#67225) -- this should be true even without the fallback gate.
+#![feature(never_type_fallback)]
+
+struct E;
+
+impl From<!> for E {
+    fn from(_: !) -> E {
+        E
+    }
+}
+
+#[allow(unreachable_code)]
+#[allow(dead_code)]
+fn foo(never: !) {
+    <E as From<!>>::from(never);  // Ok
+    <E as From<_>>::from(never);  // Inference fails here
+}
+
+fn main() { }