Prevent Send, Freeze, and Sized from being manually implemented. Close #8517.

src/librustc/middle/lang_items.rs

@@ -158,6 +158,12 @@ impl LanguageItems {
         }
     }
 
+    pub fn is_builtin_kind(&self, id: def_id) -> bool {
+        Some(id) == self.freeze_trait() ||
+        Some(id) == self.send_trait() ||
+        Some(id) == self.sized_trait()
+    }
+
     pub fn freeze_trait(&self) -> Option<def_id> {
         self.items[FreezeTraitLangItem as uint]
     }

src/librustc/middle/ty.rs

@@ -3725,6 +3725,12 @@ pub fn impl_trait_ref(cx: ctxt, id: ast::def_id) -> Option<@TraitRef> {
     return ret;
 }
 
+pub fn trait_ref_is_builtin_kind(tcx: ctxt, tr: &ast::trait_ref) -> bool {
+    let def = tcx.def_map.find(&tr.ref_id).expect("no def-map entry for trait");
+    let def_id = ast_util::def_id_of_def(*def);
+    tcx.lang_items.is_builtin_kind(def_id)
+}
+
 pub fn ty_to_def_id(ty: t) -> Option<ast::def_id> {
     match get(ty).sty {
       ty_trait(id, _, _, _, _) | ty_struct(id, _) | ty_enum(id, _) => Some(id),

src/librustc/middle/typeck/collect.rs

@@ -869,6 +869,13 @@ pub fn convert(ccx: &CrateCtxt, it: &ast::item) {
                                   &i_ty_generics, generics,
                                   parent_visibility);
         for t in opt_trait_ref.iter() {
+            // Prevent the builtin kind traits from being manually implemented.
+            if ty::trait_ref_is_builtin_kind(ccx.tcx, t) {
+                ccx.tcx.sess.span_err(it.span,
+                    "cannot provide an explicit implementation \
+                     for a builtin kind");
+            }
+
             check_methods_against_trait(ccx, generics, rp, selfty, t, cms);
         }
       }

src/test/compile-fail/cant-implement-builtin-kinds.rs

@@ -0,0 +1,19 @@
+// Copyright 2013 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.
+
+// See issue #8517 for why this should be illegal.
+
+struct X<T>(T);
+
+impl <T> Send for X<T> { } //~ ERROR cannot provide an explicit implementation for a builtin kind
+impl <T> Sized for X<T> { } //~ ERROR cannot provide an explicit implementation for a builtin kind
+impl <T> Freeze for X<T> { } //~ ERROR cannot provide an explicit implementation for a builtin kind
+
+fn main() { }