librustc: Put #[unsafe_destructor] behind a feature gate.

Closes #8142.

This is not the semantics we want long-term. You can continue to use
`#[unsafe_destructor]`, but you'll need to add
`#![feature(unsafe_destructor)]` to the crate attributes.

[breaking-change]

src/test/auxiliary/issue-2526.rs

@@ -11,6 +11,8 @@
 #![crate_id="issue_2526#0.2"]
 #![crate_type = "lib"]
 
+#![feature(unsafe_destructor)]
+
 struct arc_destruct<T> {
   _data: int,
 }

src/test/bench/task-perf-alloc-unwind.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(managed_boxes)]
+#![feature(managed_boxes, unsafe_destructor)]
 
 extern crate collections;
 extern crate time;

src/test/compile-fail/borrowck-borrowed-uniq-rvalue-2.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(unsafe_destructor)]
+
 extern crate debug;
 
 struct defer<'a> {

src/test/compile-fail/no-send-res-ports.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(managed_boxes)]
+#![feature(managed_boxes, unsafe_destructor)]
 
 extern crate debug;
 

src/test/compile-fail/pinned-deep-copy.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(managed_boxes)]
+#![feature(managed_boxes, unsafe_destructor)]
 
 extern crate debug;
 

src/test/compile-fail/unique-vec-res.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(managed_boxes)]
+#![feature(managed_boxes, unsafe_destructor)]
 
 extern crate debug;
 use std::cell::Cell;

src/test/run-fail/unwind-resource-fail3.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(managed_boxes)]
+#![feature(managed_boxes, unsafe_destructor)]
 
 // error-pattern:quux
 

src/test/run-pass/attr-no-drop-flag-size.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(unsafe_destructor)]
+
 use std::mem::size_of;
 
 #[unsafe_no_drop_flag]

src/test/run-pass/drop-trait-generic.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(unsafe_destructor)]
+
 struct S<T> {
     x: T
 }

src/test/run-pass/init-res-into-things.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(managed_boxes)]
+#![feature(managed_boxes, unsafe_destructor)]
 
 use std::cell::Cell;
 use std::gc::{Gc, GC};

src/test/run-pass/issue-2718.rs

@@ -9,6 +9,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(unsafe_destructor)]
+
 pub type Task = int;
 
 // tjc: I don't know why

src/test/run-pass/issue-2735-2.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(managed_boxes)]
+#![feature(managed_boxes, unsafe_destructor)]
 
 use std::cell::Cell;
 use std::gc::{Gc, GC};

src/test/run-pass/issue-2735-3.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(managed_boxes)]
+#![feature(managed_boxes, unsafe_destructor)]
 
 use std::cell::Cell;
 use std::gc::{Gc, GC};

src/test/run-pass/issue-4252.rs

@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+#![feature(unsafe_destructor)]
+
 extern crate debug;
 
 trait X {

src/test/run-pass/issue-979.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(managed_boxes)]
+#![feature(managed_boxes, unsafe_destructor)]
 
 use std::cell::Cell;
 use std::gc::{GC, Gc};

src/test/run-pass/newtype-struct-drop-run.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(managed_boxes)]
+#![feature(managed_boxes, unsafe_destructor)]
 
 // Make sure the destructor is run for newtype structs.
 

src/test/run-pass/option-unwrap.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(managed_boxes)]
+#![feature(managed_boxes, unsafe_destructor)]
 
 use std::cell::Cell;
 use std::gc::{GC, Gc};

src/test/run-pass/resource-assign-is-not-copy.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(managed_boxes)]
+#![feature(managed_boxes, unsafe_destructor)]
 
 extern crate debug;
 

src/test/run-pass/resource-destruct.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(managed_boxes)]
+#![feature(managed_boxes, unsafe_destructor)]
 
 use std::cell::Cell;
 use std::gc::{GC, Gc};

src/test/run-pass/resource-in-struct.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(managed_boxes)]
+#![feature(managed_boxes, unsafe_destructor)]
 
 // Ensures that class dtors run if the object is inside an enum
 // variant

src/test/run-pass/unwind-resource2.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(managed_boxes)]
+#![feature(managed_boxes, unsafe_destructor)]
 
 use std::task;
 use std::gc::{Gc, GC};

src/test/run-pass/vec-slice-drop.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![feature(managed_boxes)]
+#![feature(managed_boxes, unsafe_destructor)]
 
 use std::cell::Cell;
 use std::gc::{Gc, GC};