Auto merge of #27349 - arielb1:constant-at, r=alexcrichton

Fixes #27033
Fixes #27077 

r? @alexcrichton

src/test/compile-fail/issue-27033.rs

@@ -0,0 +1,22 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn main() {
+    match Some(1) {
+        None @ _ => {} //~ ERROR declaration of `None` shadows an enum variant
+    };
+    const C: u8 = 1;
+    match 1 {
+        C @ 2 => { //~ ERROR only irrefutable patterns allowed here
+            println!("{}", C);
+        }
+        _ => {}
+    };
+}