Auto merge of #28827 - thepowersgang:unsafe-const-fn-2, r=Aatch

This is the original test implementation, which works according to the tests I wrote, but might need a review.

src/test/compile-fail/unsafe-const-fn.rs

@@ -0,0 +1,24 @@
+// 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.
+
+// A quick test of 'unsafe const fn' functionality
+
+#![feature(const_fn)]
+
+unsafe const fn dummy(v: u32) -> u32 {
+    !v
+}
+
+const VAL: u32 = dummy(0xFFFF); //~ ERROR E0133
+
+fn main() {
+    assert_eq!(VAL, 0xFFFF0000);
+}
+

src/test/run-pass/unsafe-const-fn.rs

@@ -0,0 +1,31 @@
+// 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.
+
+// A quick test of 'unsafe const fn' functionality
+
+#![feature(const_fn)]
+
+unsafe const fn dummy(v: u32) -> u32 {
+    !v
+}
+
+struct Type;
+impl Type {
+    unsafe const fn new() -> Type {
+        Type
+    }
+}
+
+const VAL: u32 = unsafe { dummy(0xFFFF) };
+const TYPE_INST: Type = unsafe { Type::new() };
+
+fn main() {
+    assert_eq!(VAL, 0xFFFF0000);
+}