Set #[no_drop_flag] on Rc<T> and AtomicOption. Add Test

src/libextra/rc.rs

@@ -70,10 +70,12 @@ impl<T> Rc<T> {
 impl<T> Drop for Rc<T> {
     fn finalize(&self) {
         unsafe {
-            (*self.ptr).count -= 1;
-            if (*self.ptr).count == 0 {
-                ptr::replace_ptr(self.ptr, intrinsics::uninit());
-                free(self.ptr as *c_void)
+            if self.ptr.is_not_null() {
+                (*self.ptr).count -= 1;
+                if (*self.ptr).count == 0 {
+                    ptr::replace_ptr(self.ptr, intrinsics::uninit());
+                    free(self.ptr as *c_void)
+                }
             }
         }
     }
@@ -220,10 +222,12 @@ impl<T> RcMut<T> {
 impl<T> Drop for RcMut<T> {
     fn finalize(&self) {
         unsafe {
-            (*self.ptr).count -= 1;
-            if (*self.ptr).count == 0 {
-                ptr::replace_ptr(self.ptr, uninit());
-                free(self.ptr as *c_void)
+            if self.ptr.is_not_null() {
+                (*self.ptr).count -= 1;
+                if (*self.ptr).count == 0 {
+                    ptr::replace_ptr(self.ptr, uninit());
+                    free(self.ptr as *c_void)
+                }
             }
         }
     }

src/librustc/middle/ty.rs

@@ -3883,7 +3883,7 @@ impl DtorKind {
 pub fn ty_dtor(cx: ctxt, struct_id: def_id) -> DtorKind {
     match cx.destructor_for_type.find(&struct_id) {
         Some(&method_def_id) => {
-            let flag = has_attr(cx, struct_id, "no_drop_flag");
+            let flag = !has_attr(cx, struct_id, "no_drop_flag");
 
             TraitDtor(method_def_id, flag)
         }

src/libstd/unstable/atomics.rs

@@ -62,6 +62,7 @@ pub struct AtomicPtr<T> {
 /**
  * An owned atomic pointer. Ensures that only a single reference to the data is held at any time.
  */
+#[no_drop_flag]
 pub struct AtomicOption<T> {
     priv p: *mut c_void
 }

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

@@ -0,0 +1,25 @@
+// Copyright 2012 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::sys::size_of;
+
+#[no_drop_flag]
+struct Test<T> {
+    a: T
+}
+
+#[unsafe_destructor]
+impl<T> Drop for Test<T> {
+    fn finalize(&self) { }
+}
+
+fn main() {
+    assert_eq!(size_of::<int>(), size_of::<Test<int>>());
+}