trans: Keep transmutes from fn item types working, but lint them.

src/test/compile-fail/transmute-from-fn-item-types-lint.rs

@@ -0,0 +1,51 @@
+// Copyright 2016 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.
+
+use std::mem;
+
+unsafe fn foo() -> (isize, *const (), Option<fn()>) {
+    let i = mem::transmute(bar);
+    //~^ WARN is now zero-sized and has to be cast to a pointer before transmuting
+    //~^^ WARN was previously accepted
+
+    let p = mem::transmute(foo);
+    //~^ WARN is now zero-sized and has to be cast to a pointer before transmuting
+    //~^^ WARN was previously accepted
+
+    let of = mem::transmute(main);
+    //~^ WARN is now zero-sized and has to be cast to a pointer before transmuting
+    //~^^ WARN was previously accepted
+
+    (i, p, of)
+}
+
+unsafe fn bar() {
+    mem::transmute::<_, *mut ()>(foo);
+    //~^ WARN is now zero-sized and has to be cast to a pointer before transmuting
+    //~^^ WARN was previously accepted
+
+    mem::transmute::<_, fn()>(bar);
+    //~^ WARN is now zero-sized and has to be cast to a pointer before transmuting
+    //~^^ WARN was previously accepted
+
+    // No error if a coercion would otherwise occur.
+    mem::transmute::<fn(), usize>(main);
+
+    // Error, still, if the resulting type is not pointer-sized.
+    mem::transmute::<_, u8>(main);
+    //~^ ERROR transmute called with differently sized types
+}
+
+fn main() {
+    unsafe {
+        foo();
+        bar();
+    }
+}

src/test/run-pass/transmute-from-fn-item-types.rs

@@ -0,0 +1,27 @@
+// Copyright 2016 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.
+
+#![allow(transmute_from_fn_item_types)]
+
+use std::mem;
+
+fn main() {
+    unsafe {
+        let u = mem::transmute(main);
+        let p = mem::transmute(main);
+        let f = mem::transmute(main);
+        let tuple: (usize, *mut (), fn()) = (u, p, f);
+        assert_eq!(mem::transmute::<_, [usize; 3]>(tuple), [main as usize; 3]);
+
+        mem::transmute::<_, usize>(main);
+        mem::transmute::<_, *mut ()>(main);
+        mem::transmute::<_, fn()>(main);
+    }
+}