Add UI test for E0379

Author: KiChjang

src/test/ui/mismatched_types/const-fn-in-trait.rs

@@ -0,0 +1,25 @@
+// 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.
+
+// rustc-env:RUST_NEW_ERROR_FORMAT
+
+#![feature(const_fn)]
+
+trait Foo {
+    fn f() -> u32;
+    const fn g();
+}
+
+impl Foo for u32 {
+    const fn f() -> u32 { 22 }
+    fn g() {}
+}
+
+fn main() { }

src/test/ui/mismatched_types/const-fn-in-trait.stderr

@@ -0,0 +1,14 @@
+error[E0379]: trait fns cannot be declared const
+  --> $DIR/const-fn-in-trait.rs:17:5
+   |
+17 |     const fn g();
+   |     ^^^^^ trait fns cannot be const
+
+error[E0379]: trait fns cannot be declared const
+  --> $DIR/const-fn-in-trait.rs:21:5
+   |
+21 |     const fn f() -> u32 { 22 }
+   |     ^^^^^ trait fns cannot be const
+
+error: aborting due to 2 previous errors
+