Turn type_id into a constant intrinsic

Add rustc_const_unstable attribute for `any::TypeId::of`

Add test for `const fn TypeId::of`

src/test/compile-fail/const-typeid-of.rs

@@ -0,0 +1,18 @@
+// Copyright 2018 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::any::TypeId;
+
+struct A;
+
+fn main() {
+    const A_ID: TypeId = TypeId::of::<A>();
+    //~^ ERROR `std::any::TypeId::of` is not yet stable as a const fn
+}

src/test/run-pass/const-typeid-of.rs

@@ -0,0 +1,43 @@
+// Copyright 2018 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.
+
+#![feature(core_intrinsics)]
+#![feature(const_type_id)]
+
+use std::any::TypeId;
+
+struct A;
+
+static ID_ISIZE: TypeId = TypeId::of::<isize>();
+
+pub fn main() {
+    assert_eq!(ID_ISIZE, TypeId::of::<isize>());
+
+    // sanity test of TypeId
+    const T: (TypeId, TypeId, TypeId) = (TypeId::of::<usize>(),
+                     TypeId::of::<&'static str>(),
+                     TypeId::of::<A>());
+    let (d, e, f) = (TypeId::of::<usize>(), TypeId::of::<&'static str>(),
+                     TypeId::of::<A>());
+
+    assert!(T.0 != T.1);
+    assert!(T.0 != T.2);
+    assert!(T.1 != T.2);
+
+    assert_eq!(T.0, d);
+    assert_eq!(T.1, e);
+    assert_eq!(T.2, f);
+
+    // Check fn pointer against collisions
+    const F: (TypeId, TypeId) = (TypeId::of::<fn(fn(A) -> A) -> A>(),
+            TypeId::of::<fn(fn() -> A, A) -> A>());
+
+    assert!(F.0 != F.1);
+}