Auto merge of #18875 - servo:stable-js, r=nox,jdm

Remove the need for rust-mozjs to use unstable Rust features

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44 files changed, 266 insertions, 216 deletions

diff --git a/Cargo.lock b/Cargo.lock
index e3863a5d944..b3629688a63 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1457,7 +1457,7 @@ dependencies = [
 [[package]]
 name = "js"
 version = "0.1.6"
-source = "git+https://github.com/servo/rust-mozjs#3de4ff3d52361a47a17e3b4fcb02c779b99d93d4"
+source = "git+https://github.com/servo/rust-mozjs#cdb9570900b74cf4e0ba129eeb8bf527cee3ddb5"
 dependencies = [
  "cmake 0.1.22 (registry+https://github.com/rust-lang/crates.io-index)",
  "heapsize 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2618,6 +2618,7 @@ dependencies = [
  "mitochondria 1.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "msg 0.0.1",
  "net_traits 0.0.1",
+ "nonzero 0.0.1",
  "num-traits 0.1.37 (registry+https://github.com/rust-lang/crates.io-index)",
  "offscreen_gl_context 0.11.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "open 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
diff --git a/components/canvas_traits/webgl.rs b/components/canvas_traits/webgl.rs
index fb555b265b3..9d53e93287f 100644
--- a/components/canvas_traits/webgl.rs
+++ b/components/canvas_traits/webgl.rs
@@ -3,7 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use euclid::Size2D;
-use nonzero::NonZeroU32;
+use nonzero::NonZero;
 use offscreen_gl_context::{GLContextAttributes, GLLimits};
 use std::fmt;
 use webrender_api::{DocumentId, ImageKey, PipelineId};
@@ -253,13 +253,13 @@ pub enum WebGLCommand {
 macro_rules! define_resource_id_struct {
     ($name:ident) => {
         #[derive(Clone, Copy, Eq, Hash, PartialEq)]
-        pub struct $name(NonZeroU32);
+        pub struct $name(NonZero<u32>);
 
         impl $name {
             #[allow(unsafe_code)]
             #[inline]
             pub unsafe fn new(id: u32) -> Self {
-                $name(NonZeroU32::new_unchecked(id))
+                $name(NonZero::new_unchecked(id))
             }
 
             #[inline]
diff --git a/components/compositing/compositor.rs b/components/compositing/compositor.rs
index 7e77157b845..85bab91a835 100644
--- a/components/compositing/compositor.rs
+++ b/components/compositing/compositor.rs
@@ -13,7 +13,7 @@ use image::{DynamicImage, ImageFormat, RgbImage};
 use ipc_channel::ipc::{self, IpcSharedMemory};
 use msg::constellation_msg::{PipelineId, PipelineIndex, PipelineNamespaceId};
 use net_traits::image::base::{Image, PixelFormat};
-use nonzero::NonZeroU32;
+use nonzero::NonZero;
 use profile_traits::time::{self, ProfilerCategory, profile};
 use script_traits::{AnimationState, AnimationTickType, ConstellationControlMsg};
 use script_traits::{ConstellationMsg, LayoutControlMsg, MouseButton};
@@ -62,7 +62,7 @@ impl ConvertPipelineIdFromWebRender for webrender_api::PipelineId {
     fn from_webrender(&self) -> PipelineId {
         PipelineId {
             namespace_id: PipelineNamespaceId(self.0),
-            index: PipelineIndex(NonZeroU32::new(self.1).expect("Webrender pipeline zero?")),
+            index: PipelineIndex(NonZero::new(self.1).expect("Webrender pipeline zero?")),
         }
     }
 }
diff --git a/components/layout_thread/dom_wrapper.rs b/components/layout_thread/dom_wrapper.rs
index 2863d840ce5..08d628a6d6c 100644
--- a/components/layout_thread/dom_wrapper.rs
+++ b/components/layout_thread/dom_wrapper.rs
@@ -36,7 +36,7 @@ use html5ever::{LocalName, Namespace};
 use layout::data::StyleAndLayoutData;
 use layout::wrapper::GetRawData;
 use msg::constellation_msg::{BrowsingContextId, PipelineId};
-use nonzero::NonZeroUsize;
+use nonzero::NonZero;
 use range::Range;
 use script::layout_exports::{CAN_BE_FRAGMENTED, HAS_DIRTY_DESCENDANTS, IS_IN_DOC};
 use script::layout_exports::{CharacterDataTypeId, ElementTypeId, HTMLElementTypeId, NodeTypeId};
@@ -235,8 +235,7 @@ impl<'ln> LayoutNode for ServoLayoutNode<'ln> {
             let ptr: *mut StyleAndLayoutData =
                 Box::into_raw(Box::new(StyleAndLayoutData::new()));
             let opaque = OpaqueStyleAndLayoutData {
-                ptr: NonZeroUsize::new_unchecked(ptr as usize),
-                phantom: PhantomData,
+                ptr: NonZero::new_unchecked(ptr as *mut StyleData),
             };
             self.init_style_and_layout_data(opaque);
         };
diff --git a/components/msg/constellation_msg.rs b/components/msg/constellation_msg.rs
index da9bb3ea0cb..40c1827b262 100644
--- a/components/msg/constellation_msg.rs
+++ b/components/msg/constellation_msg.rs
@@ -5,7 +5,7 @@
 //! The high-level interface from script to constellation. Using this abstract interface helps
 //! reduce coupling between these two components.
 
-use nonzero::NonZeroU32;
+use nonzero::NonZero;
 use std::cell::Cell;
 use std::fmt;
 use webrender_api;
@@ -195,9 +195,9 @@ impl PipelineNamespace {
         });
     }
 
-    fn next_index(&mut self) -> NonZeroU32 {
+    fn next_index(&mut self) -> NonZero<u32> {
         self.index += 1;
-        NonZeroU32::new(self.index).expect("pipeline id index wrapped!")
+        NonZero::new(self.index).expect("pipeline id index wrapped!")
     }
 
     fn next_pipeline_id(&mut self) -> PipelineId {
@@ -221,7 +221,7 @@ thread_local!(pub static PIPELINE_NAMESPACE: Cell<Option<PipelineNamespace>> = C
 pub struct PipelineNamespaceId(pub u32);
 
 #[derive(Clone, Copy, Debug, Deserialize, Eq, Hash, Ord, PartialEq, PartialOrd, Serialize)]
-pub struct PipelineIndex(pub NonZeroU32);
+pub struct PipelineIndex(pub NonZero<u32>);
 known_heap_size!(0, PipelineIndex);
 
 #[derive(Clone, Copy, Debug, Deserialize, Eq, Hash, HeapSizeOf, Ord, PartialEq, PartialOrd, Serialize)]
@@ -264,7 +264,7 @@ impl fmt::Display for PipelineId {
 }
 
 #[derive(Clone, Copy, Debug, Deserialize, Eq, Hash, Ord, PartialEq, PartialOrd, Serialize)]
-pub struct BrowsingContextIndex(pub NonZeroU32);
+pub struct BrowsingContextIndex(pub NonZero<u32>);
 known_heap_size!(0, BrowsingContextIndex);
 
 #[derive(Clone, Copy, Debug, Deserialize, Eq, Hash, HeapSizeOf, Ord, PartialEq, PartialOrd, Serialize)]
@@ -340,13 +340,13 @@ impl PartialEq<BrowsingContextId> for TopLevelBrowsingContextId {
 pub const TEST_NAMESPACE: PipelineNamespaceId = PipelineNamespaceId(1234);
 #[allow(unsafe_code)]
 #[cfg(feature = "unstable")]
-pub const TEST_PIPELINE_INDEX: PipelineIndex = unsafe { PipelineIndex(NonZeroU32::new_unchecked(5678)) };
+pub const TEST_PIPELINE_INDEX: PipelineIndex = unsafe { PipelineIndex(NonZero::new_unchecked(5678)) };
 #[cfg(feature = "unstable")]
 pub const TEST_PIPELINE_ID: PipelineId = PipelineId { namespace_id: TEST_NAMESPACE, index: TEST_PIPELINE_INDEX };
 #[allow(unsafe_code)]
 #[cfg(feature = "unstable")]
 pub const TEST_BROWSING_CONTEXT_INDEX: BrowsingContextIndex =
-    unsafe { BrowsingContextIndex(NonZeroU32::new_unchecked(8765)) };
+    unsafe { BrowsingContextIndex(NonZero::new_unchecked(8765)) };
 #[cfg(feature = "unstable")]
 pub const TEST_BROWSING_CONTEXT_ID: BrowsingContextId =
     BrowsingContextId { namespace_id: TEST_NAMESPACE, index: TEST_BROWSING_CONTEXT_INDEX };
diff --git a/components/nonzero/lib.rs b/components/nonzero/lib.rs
index 6682740f34e..b44cf73c7d6 100644
--- a/components/nonzero/lib.rs
+++ b/components/nonzero/lib.rs
@@ -9,7 +9,7 @@
 #![cfg_attr(feature = "unstable", feature(const_fn))]
 #![cfg_attr(feature = "unstable", feature(const_nonzero_new))]
 
-#[macro_use]
+#[cfg_attr(not(feature = "unstable"), macro_use)]
 extern crate serde;
 
 pub use imp::*;
@@ -17,105 +17,125 @@ pub use imp::*;
 #[cfg(feature = "unstable")]
 mod imp {
     extern crate core;
-    use self::core::nonzero::NonZero;
+    use self::core::nonzero::NonZero as CoreNonZero;
+    use serde::{Serialize, Serializer, Deserialize, Deserializer};
 
-    #[derive(Clone, Copy, Debug, Deserialize, Eq, Hash, Ord, PartialEq, PartialOrd, Serialize)]
-    pub struct NonZeroU32(NonZero<u32>);
+    pub use self::core::nonzero::Zeroable;
 
-    #[derive(Clone, Copy, Debug, Deserialize, Eq, Hash, Ord, PartialEq, PartialOrd, Serialize)]
-    pub struct NonZeroUsize(NonZero<usize>);
+    #[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
+    pub struct NonZero<T: Zeroable>(CoreNonZero<T>);
+
+    impl<T: Zeroable> NonZero<T> {
+        #[inline]
+        pub const unsafe fn new_unchecked(x: T) -> Self {
+            NonZero(CoreNonZero::new_unchecked(x))
+        }
+
+        #[inline]
+        pub fn new(x: T) -> Option<Self> {
+            CoreNonZero::new(x).map(NonZero)
+        }
+
+        #[inline]
+        pub fn get(self) -> T {
+            self.0.get()
+        }
+    }
 
-    impl NonZeroU32 {
-        #[inline] pub const unsafe fn new_unchecked(x: u32) -> Self { NonZeroU32(NonZero::new_unchecked(x)) }
-        #[inline] pub fn new(x: u32) -> Option<Self> { NonZero::new(x).map(NonZeroU32) }
-        #[inline] pub fn get(self) -> u32 { self.0.get() }
+    // Not using derive because of the additional Clone bound required by the inner impl
+
+    impl<T> Serialize for NonZero<T>
+    where
+        T: Serialize + Zeroable + Clone,
+    {
+        fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+        where
+            S: Serializer,
+        {
+            self.0.serialize(serializer)
+        }
     }
 
-    impl NonZeroUsize {
-        #[inline] pub const unsafe fn new_unchecked(x: usize) -> Self { NonZeroUsize(NonZero::new_unchecked(x)) }
-        #[inline] pub fn new(x: usize) -> Option<Self> { NonZero::new(x).map(NonZeroUsize) }
-        #[inline] pub fn get(self) -> usize { self.0.get() }
+    impl<'de, T> Deserialize<'de> for NonZero<T>
+    where
+        T: Deserialize<'de> + Zeroable,
+    {
+        fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+        where
+            D: Deserializer<'de>,
+        {
+            CoreNonZero::deserialize(deserializer).map(NonZero)
+        }
     }
 }
 
 #[cfg(not(feature = "unstable"))]
 mod imp {
-    use std::cmp;
-    use std::hash;
-
     #[derive(Clone, Copy, Debug, Deserialize, Eq, Hash, Ord, PartialEq, PartialOrd, Serialize)]
-    pub struct NonZeroU32(u32);
+    pub struct NonZero<T: Zeroable>(T);
 
-    impl NonZeroU32 {
+    impl<T: Zeroable> NonZero<T> {
         #[inline]
-        pub fn new(x: u32) -> Option<Self> {
-            if x != 0 {
-                Some(NonZeroU32(x))
-            } else {
-                None
-            }
+        pub unsafe fn new_unchecked(x: T) -> Self {
+            NonZero(x)
         }
 
         #[inline]
-        pub unsafe fn new_unchecked(x: u32) -> Self {
-            NonZeroU32(x)
-        }
-
-        #[inline]
-        pub fn get(self) -> u32 {
-            self.0
-        }
-    }
-
-    #[derive(Clone, Copy, Debug, Eq)]
-    pub struct NonZeroUsize(&'static ());
-
-    impl NonZeroUsize {
-        #[inline]
-        pub fn new(x: usize) -> Option<Self> {
-            if x != 0 {
-                Some(unsafe { Self::new_unchecked(x) })
-            } else {
+        pub fn new(x: T) -> Option<Self> {
+            if x.is_zero() {
                 None
+            } else {
+                Some(NonZero(x))
             }
         }
 
         #[inline]
-        pub unsafe fn new_unchecked(x: usize) -> Self {
-            NonZeroUsize(&*(x as *const ()))
+        pub fn get(self) -> T {
+            self.0
         }
+    }
 
-        #[inline]
-        pub fn get(self) -> usize {
-            self.0 as *const () as usize
-        }
+    /// Unsafe trait to indicate what types are usable with the NonZero struct
+    pub unsafe trait Zeroable {
+        /// Whether this value is zero
+        fn is_zero(&self) -> bool;
     }
 
-    impl PartialEq for NonZeroUsize {
-        #[inline]
-        fn eq(&self, other: &Self) -> bool {
-            self.get() == other.get()
+    macro_rules! impl_zeroable_for_pointer_types {
+        ( $( $Ptr: ty )+ ) => {
+            $(
+                /// For fat pointers to be considered "zero", only the "data" part needs to be null.
+                unsafe impl<T: ?Sized> Zeroable for $Ptr {
+                    #[inline]
+                    fn is_zero(&self) -> bool {
+                        // Cast because `is_null` is only available on thin pointers
+                        (*self as *mut u8).is_null()
+                    }
+                }
+            )+
         }
     }
 
-    impl PartialOrd for NonZeroUsize {
-        #[inline]
-        fn partial_cmp(&self, other: &Self) -> Option<cmp::Ordering> {
-            self.get().partial_cmp(&other.get())
+    macro_rules! impl_zeroable_for_integer_types {
+        ( $( $Int: ty )+ ) => {
+            $(
+                unsafe impl Zeroable for $Int {
+                    #[inline]
+                    fn is_zero(&self) -> bool {
+                        *self == 0
+                    }
+                }
+            )+
         }
     }
 
-    impl Ord for NonZeroUsize {
-        #[inline]
-        fn cmp(&self, other: &Self) -> cmp::Ordering {
-            self.get().cmp(&other.get())
-        }
+    impl_zeroable_for_pointer_types! {
+        *const T
+        *mut T
     }
 
-    impl hash::Hash for NonZeroUsize {
-        #[inline]
-        fn hash<H: hash::Hasher>(&self, hasher: &mut H) {
-            self.get().hash(hasher)
-        }
+    impl_zeroable_for_integer_types! {
+        usize u8 u16 u32 u64
+        isize i8 i16 i32 i64
     }
 }
diff --git a/components/remutex/lib.rs b/components/remutex/lib.rs
index 2589a6d1162..5fbbad40bf0 100644
--- a/components/remutex/lib.rs
+++ b/components/remutex/lib.rs
@@ -14,7 +14,7 @@ extern crate nonzero;
 #[macro_use] extern crate lazy_static;
 #[macro_use] extern crate log;
 
-use nonzero::NonZeroUsize;
+use nonzero::NonZero;
 use std::cell::{Cell, UnsafeCell};
 use std::ops::Deref;
 use std::sync::{LockResult, Mutex, MutexGuard, PoisonError, TryLockError, TryLockResult};
@@ -25,7 +25,7 @@ use std::sync::atomic::{AtomicUsize, Ordering};
 // TODO: can we use the thread-id crate for this?
 
 #[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
-pub struct ThreadId(NonZeroUsize);
+pub struct ThreadId(NonZero<usize>);
 
 lazy_static!{ static ref THREAD_COUNT: AtomicUsize = AtomicUsize::new(1); }
 
@@ -33,7 +33,7 @@ impl ThreadId {
     #[allow(unsafe_code)]
     fn new() -> ThreadId {
         let number = THREAD_COUNT.fetch_add(1, Ordering::SeqCst);
-        ThreadId(NonZeroUsize::new(number).unwrap())
+        ThreadId(NonZero::new(number).unwrap())
     }
     pub fn current() -> ThreadId {
         THREAD_ID.with(|tls| tls.clone())
@@ -57,13 +57,13 @@ impl AtomicOptThreadId {
     #[allow(unsafe_code)]
     pub fn load(&self, ordering: Ordering) -> Option<ThreadId> {
         let number = self.0.load(ordering);
-        NonZeroUsize::new(number).map(ThreadId)
+        NonZero::new(number).map(ThreadId)
     }
     #[allow(unsafe_code)]
     pub fn swap(&self, value: Option<ThreadId>, ordering: Ordering) -> Option<ThreadId> {
         let number = value.map(|id| id.0.get()).unwrap_or(0);
         let number = self.0.swap(number, ordering);
-        NonZeroUsize::new(number).map(ThreadId)
+        NonZero::new(number).map(ThreadId)
     }
 }
 
diff --git a/components/script/Cargo.toml b/components/script/Cargo.toml
index 9bb7f932cd4..7e0c4068cec 100644
--- a/components/script/Cargo.toml
+++ b/components/script/Cargo.toml
@@ -13,6 +13,7 @@ path = "lib.rs"
 
 [features]
 debugmozjs = ['js/debugmozjs']
+unstable = []
 
 [build-dependencies]
 cmake = "0.1"
@@ -61,6 +62,7 @@ mime = "0.2.1"
 mime_guess = "1.8.0"
 msg = {path = "../msg"}
 net_traits = {path = "../net_traits"}
+nonzero = {path = "../nonzero"}
 num-traits = "0.1.32"
 offscreen_gl_context = { version = "0.11", features = ["serde"] }
 open = "1.1.1"
diff --git a/components/script/dom/bindings/cell.rs b/components/script/dom/bindings/cell.rs
index 2ae54fce97a..2235e3ac769 100644
--- a/components/script/dom/bindings/cell.rs
+++ b/components/script/dom/bindings/cell.rs
@@ -9,7 +9,7 @@ use style::thread_state;
 
 /// A mutable field in the DOM.
 ///
-/// This extends the API of `core::cell::RefCell` to allow unsafe access in
+/// This extends the API of `std::cell::RefCell` to allow unsafe access in
 /// certain situations, with dynamic checking in debug builds.
 #[derive(Clone, Debug, Default, HeapSizeOf, PartialEq)]
 pub struct DomRefCell<T> {
@@ -57,7 +57,7 @@ impl<T> DomRefCell<T> {
     }
 }
 
-// Functionality duplicated with `core::cell::RefCell`
+// Functionality duplicated with `std::cell::RefCell`
 // ===================================================
 impl<T> DomRefCell<T> {
     /// Create a new `DomRefCell` containing `value`.
diff --git a/components/script/dom/bindings/codegen/CodegenRust.py b/components/script/dom/bindings/codegen/CodegenRust.py
index a82ad040041..d0b5e678db8 100644
--- a/components/script/dom/bindings/codegen/CodegenRust.py
+++ b/components/script/dom/bindings/codegen/CodegenRust.py
@@ -1407,7 +1407,7 @@ def getRetvalDeclarationForType(returnType, descriptorProvider):
     if returnType.isAny():
         return CGGeneric("JSVal")
     if returnType.isObject() or returnType.isSpiderMonkeyInterface():
-        result = CGGeneric("NonZero<*mut JSObject>")
+        result = CGGeneric("NonNullJSObjectPtr")
         if returnType.nullable():
             result = CGWrapper(result, pre="Option<", post=">")
         return result
@@ -2253,6 +2253,7 @@ def UnionTypes(descriptors, dictionaries, callbacks, typedefs, config):
         'dom::bindings::conversions::StringificationBehavior',
         'dom::bindings::conversions::root_from_handlevalue',
         'dom::bindings::error::throw_not_in_union',
+        'dom::bindings::nonnull::NonNullJSObjectPtr',
         'dom::bindings::mozmap::MozMap',
         'dom::bindings::root::DomRoot',
         'dom::bindings::str::ByteString',
@@ -3659,19 +3660,18 @@ class CGMemberJITInfo(CGThing):
                     call: ${opName} as *const os::raw::c_void,
                     protoID: PrototypeList::ID::${name} as u16,
                     depth: ${depth},
-                    _bitfield_1:
-                        JSJitInfo::new_bitfield_1(
-                            JSJitInfo_OpType::${opType} as u8,
-                            JSJitInfo_AliasSet::${aliasSet} as u8,
-                            JSValueType::${returnType} as u8,
-                            ${isInfallible},
-                            ${isMovable},
-                            ${isEliminatable},
-                            ${isAlwaysInSlot},
-                            ${isLazilyCachedInSlot},
-                            ${isTypedMethod},
-                            ${slotIndex} as u16,
-                        )
+                    _bitfield_1: new_jsjitinfo_bitfield_1!(
+                        JSJitInfo_OpType::${opType} as u8,
+                        JSJitInfo_AliasSet::${aliasSet} as u8,
+                        JSValueType::${returnType} as u8,
+                        ${isInfallible},
+                        ${isMovable},
+                        ${isEliminatable},
+                        ${isAlwaysInSlot},
+                        ${isLazilyCachedInSlot},
+                        ${isTypedMethod},
+                        ${slotIndex},
+                    ),
                 }
                 """,
                 opName=opName,
@@ -5574,7 +5574,6 @@ def generate_imports(config, cgthings, descriptors, callbacks=None, dictionaries
         typedefs = []
 
     return CGImports(cgthings, descriptors, callbacks, dictionaries, enums, typedefs, [
-        'core::nonzero::NonZero',
         'js',
         'js::JSCLASS_GLOBAL_SLOT_COUNT',
         'js::JSCLASS_IS_DOMJSCLASS',
@@ -5785,6 +5784,7 @@ def generate_imports(config, cgthings, descriptors, callbacks=None, dictionaries
         'dom::bindings::proxyhandler::get_expando_object',
         'dom::bindings::proxyhandler::get_property_descriptor',
         'dom::bindings::mozmap::MozMap',
+        'dom::bindings::nonnull::NonNullJSObjectPtr',
         'dom::bindings::num::Finite',
         'dom::bindings::str::ByteString',
         'dom::bindings::str::DOMString',
diff --git a/components/script/dom/bindings/conversions.rs b/components/script/dom/bindings/conversions.rs
index 075f681308e..e27813d20f9 100644
--- a/components/script/dom/bindings/conversions.rs
+++ b/components/script/dom/bindings/conversions.rs
@@ -34,6 +34,7 @@
 
 use dom::bindings::error::{Error, Fallible};
 use dom::bindings::inheritance::Castable;
+use dom::bindings::nonnull::NonNullJSObjectPtr;
 use dom::bindings::num::Finite;
 use dom::bindings::reflector::{DomObject, Reflector};
 use dom::bindings::root::DomRoot;
@@ -53,7 +54,7 @@ use js::jsapi::{JS_GetLatin1StringCharsAndLength, JS_GetProperty, JS_GetReserved
 use js::jsapi::{JS_GetTwoByteStringCharsAndLength, JS_IsArrayObject, JS_IsExceptionPending};
 use js::jsapi::{JS_NewStringCopyN, JS_StringHasLatin1Chars, MutableHandleValue};
 use js::jsval::{ObjectValue, StringValue, UndefinedValue};
-use js::rust::{ToString, get_object_class, is_dom_class, is_dom_object, maybe_wrap_value};
+use js::rust::{ToString, get_object_class, is_dom_class, is_dom_object, maybe_wrap_value, maybe_wrap_object_value};
 use libc;
 use num_traits::Float;
 use servo_config::opts;
@@ -66,9 +67,19 @@ pub trait IDLInterface {
 }
 
 /// A trait to mark an IDL interface as deriving from another one.
-#[rustc_on_unimplemented = "The IDL interface `{Self}` is not derived from `{T}`."]
+#[cfg_attr(feature = "unstable",
+           rustc_on_unimplemented = "The IDL interface `{Self}` is not derived from `{T}`.")]
 pub trait DerivedFrom<T: Castable>: Castable {}
 
+// https://heycam.github.io/webidl/#es-object
+impl ToJSValConvertible for NonNullJSObjectPtr {
+    #[inline]
+    unsafe fn to_jsval(&self, cx: *mut JSContext, rval: MutableHandleValue) {
+        rval.set(ObjectValue(self.get()));
+        maybe_wrap_object_value(cx, rval);
+    }
+}
+
 impl<T: Float + ToJSValConvertible> ToJSValConvertible for Finite<T> {
     #[inline]
     unsafe fn to_jsval(&self, cx: *mut JSContext, rval: MutableHandleValue) {
diff --git a/components/script/dom/bindings/interface.rs b/components/script/dom/bindings/interface.rs
index 6203f17bfb9..3cb9aab9f72 100644
--- a/components/script/dom/bindings/interface.rs
+++ b/components/script/dom/bindings/interface.rs
@@ -134,8 +134,8 @@ impl NonCallbackInterfaceObjectClass {
                 name: b"Function\0" as *const _ as *const libc::c_char,
                 flags: 0,
                 cOps: &constructor_behavior.0,
-                spec: ptr::null(),
-                ext: ptr::null(),
+                spec: 0 as *const _,
+                ext: 0 as *const _,
                 oOps: &OBJECT_OPS,
             },
             proto_id: proto_id,
diff --git a/components/script/dom/bindings/iterable.rs b/components/script/dom/bindings/iterable.rs
index 33d4e3339cb..779695918c9 100644
--- a/components/script/dom/bindings/iterable.rs
+++ b/components/script/dom/bindings/iterable.rs
@@ -6,17 +6,17 @@
 
 //! Implementation of `iterable<...>` and `iterable<..., ...>` WebIDL declarations.
 
-use core::nonzero::NonZero;
 use dom::bindings::codegen::Bindings::IterableIteratorBinding::IterableKeyAndValueResult;
 use dom::bindings::codegen::Bindings::IterableIteratorBinding::IterableKeyOrValueResult;
 use dom::bindings::error::Fallible;
+use dom::bindings::nonnull::NonNullJSObjectPtr;
 use dom::bindings::reflector::{DomObject, Reflector, reflect_dom_object};
 use dom::bindings::root::{Dom, DomRoot};
 use dom::bindings::trace::JSTraceable;
 use dom::globalscope::GlobalScope;
 use dom_struct::dom_struct;
 use js::conversions::ToJSValConvertible;
-use js::jsapi::{HandleValue, Heap, JSContext, JSObject, MutableHandleObject};
+use js::jsapi::{HandleValue, Heap, JSContext, MutableHandleObject};
 use js::jsval::UndefinedValue;
 use std::cell::Cell;
 use std::ptr;
@@ -73,7 +73,7 @@ impl<T: DomObject + JSTraceable + Iterable> IterableIterator<T> {
 
     /// Return the next value from the iterable object.
     #[allow(non_snake_case)]
-    pub fn Next(&self, cx: *mut JSContext) -> Fallible<NonZero<*mut JSObject>> {
+    pub fn Next(&self, cx: *mut JSContext) -> Fallible<NonNullJSObjectPtr> {
         let index = self.index.get();
         rooted!(in(cx) let mut value = UndefinedValue());
         rooted!(in(cx) let mut rval = ptr::null_mut());
@@ -106,7 +106,7 @@ impl<T: DomObject + JSTraceable + Iterable> IterableIterator<T> {
         self.index.set(index + 1);
         result.map(|_| {
             assert!(!rval.is_null());
-            unsafe { NonZero::new_unchecked(rval.get()) }
+            unsafe { NonNullJSObjectPtr::new_unchecked(rval.get()) }
         })
     }
 }
diff --git a/components/script/dom/bindings/mod.rs b/components/script/dom/bindings/mod.rs
index f251f0bd364..7cd90547105 100644
--- a/components/script/dom/bindings/mod.rs
+++ b/components/script/dom/bindings/mod.rs
@@ -144,6 +144,7 @@ pub mod interface;
 pub mod iterable;
 pub mod mozmap;
 pub mod namespace;
+pub mod nonnull;
 pub mod num;
 pub mod proxyhandler;
 pub mod refcounted;
diff --git a/components/script/dom/bindings/namespace.rs b/components/script/dom/bindings/namespace.rs
index 8ca1116ea1e..c2d58ef72c3 100644
--- a/components/script/dom/bindings/namespace.rs
+++ b/components/script/dom/bindings/namespace.rs
@@ -8,7 +8,6 @@ use dom::bindings::guard::Guard;
 use dom::bindings::interface::{create_object, define_on_global_object};
 use js::jsapi::{HandleObject, JSClass, JSContext, JSFunctionSpec, MutableHandleObject};
 use libc;
-use std::ptr;
 
 /// The class of a namespace object.
 #[derive(Clone, Copy)]
@@ -22,8 +21,8 @@ impl NamespaceObjectClass {
         NamespaceObjectClass(JSClass {
             name: name as *const _ as *const libc::c_char,
             flags: 0,
-            cOps: ptr::null_mut(),
-            reserved: [ptr::null_mut(); 3],
+            cOps: 0 as *mut _,
+            reserved: [0 as *mut _; 3],
         })
     }
 }
diff --git a/components/script/dom/bindings/nonnull.rs b/components/script/dom/bindings/nonnull.rs
new file mode 100644
index 00000000000..36dade7136b
--- /dev/null
+++ b/components/script/dom/bindings/nonnull.rs
@@ -0,0 +1,24 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+//! A wrapper type for `NonZero<*mut JSObject>`, to enable local trait impls
+
+use js::jsapi::JSObject;
+use nonzero::NonZero;
+
+/// A wrapper type for `NonZero<*mut JSObject>`, to enable local trait impls
+#[derive(Clone, Copy)]
+pub struct NonNullJSObjectPtr(NonZero<*mut JSObject>);
+
+impl NonNullJSObjectPtr {
+    #[inline]
+    pub unsafe fn new_unchecked(ptr: *mut JSObject) -> Self {
+        NonNullJSObjectPtr(NonZero::new_unchecked(ptr))
+    }
+
+    #[inline]
+    pub fn get(self) -> *mut JSObject {
+        self.0.get()
+    }
+}
diff --git a/components/script/dom/bindings/root.rs b/components/script/dom/bindings/root.rs
index 5aaa806ceaf..87525900448 100644
--- a/components/script/dom/bindings/root.rs
+++ b/components/script/dom/bindings/root.rs
@@ -24,7 +24,6 @@
 //! originating `DomRoot<T>`.
 //!
 
-use core::nonzero::NonZero;
 use dom::bindings::conversions::DerivedFrom;
 use dom::bindings::inheritance::Castable;
 use dom::bindings::reflector::{DomObject, Reflector};
@@ -35,12 +34,11 @@ use heapsize::HeapSizeOf;
 use js::jsapi::{JSObject, JSTracer, Heap};
 use js::rust::GCMethods;
 use mitochondria::OnceCell;
+use nonzero::NonZero;
 use script_layout_interface::TrustedNodeAddress;
 use std::cell::{Cell, UnsafeCell};
 use std::default::Default;
 use std::hash::{Hash, Hasher};
-#[cfg(debug_assertions)]
-use std::intrinsics::type_name;
 use std::marker::PhantomData;
 use std::mem;
 use std::ops::Deref;
@@ -359,11 +357,11 @@ impl<T: DomObject> Deref for Dom<T> {
 
 unsafe impl<T: DomObject> JSTraceable for Dom<T> {
     unsafe fn trace(&self, trc: *mut JSTracer) {
-        #[cfg(debug_assertions)]
-        let trace_str = format!("for {} on heap", type_name::<T>());
-        #[cfg(debug_assertions)]
+        #[cfg(all(feature = "unstable", debug_assertions))]
+        let trace_str = format!("for {} on heap", ::std::intrinsics::type_name::<T>());
+        #[cfg(all(feature = "unstable", debug_assertions))]
         let trace_info = &trace_str[..];
-        #[cfg(not(debug_assertions))]
+        #[cfg(not(all(feature = "unstable", debug_assertions)))]
         let trace_info = "for DOM object on heap";
 
         trace_reflector(trc,
diff --git a/components/script/dom/bindings/weakref.rs b/components/script/dom/bindings/weakref.rs
index e3cff6175b5..36eac4c4f32 100644
--- a/components/script/dom/bindings/weakref.rs
+++ b/components/script/dom/bindings/weakref.rs
@@ -11,7 +11,6 @@
 //! slot. When all associated `WeakRef` values are dropped, the
 //! `WeakBox` itself is dropped too.
 
-use core::nonzero::NonZero;
 use dom::bindings::reflector::DomObject;
 use dom::bindings::root::DomRoot;
 use dom::bindings::trace::JSTraceable;
@@ -19,6 +18,7 @@ use heapsize::HeapSizeOf;
 use js::jsapi::{JSTracer, JS_GetReservedSlot, JS_SetReservedSlot};
 use js::jsval::PrivateValue;
 use libc::c_void;
+use nonzero::NonZero;
 use std::cell::{Cell, UnsafeCell};
 use std::mem;
 use std::ops::{Deref, DerefMut, Drop};
diff --git a/components/script/dom/bluetooth.rs b/components/script/dom/bluetooth.rs
index 7da30e027cd..f9ab60ec59c 100644
--- a/components/script/dom/bluetooth.rs
+++ b/components/script/dom/bluetooth.rs
@@ -7,7 +7,6 @@ use bluetooth_traits::{BluetoothResponse, BluetoothResponseResult};
 use bluetooth_traits::blocklist::{Blocklist, uuid_is_blocklisted};
 use bluetooth_traits::scanfilter::{BluetoothScanfilter, BluetoothScanfilterSequence};
 use bluetooth_traits::scanfilter::{RequestDeviceoptions, ServiceUUIDSequence};
-use core::clone::Clone;
 use dom::bindings::cell::DomRefCell;
 use dom::bindings::codegen::Bindings::BluetoothBinding::{self, BluetoothDataFilterInit, BluetoothLEScanFilterInit};
 use dom::bindings::codegen::Bindings::BluetoothBinding::{BluetoothMethods, RequestDeviceOptions};
diff --git a/components/script/dom/crypto.rs b/components/script/dom/crypto.rs
index 2093c1cff50..ac56e9f3ff6 100644
--- a/components/script/dom/crypto.rs
+++ b/components/script/dom/crypto.rs
@@ -2,11 +2,11 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-use core::nonzero::NonZero;
 use dom::bindings::cell::DomRefCell;
 use dom::bindings::codegen::Bindings::CryptoBinding;
 use dom::bindings::codegen::Bindings::CryptoBinding::CryptoMethods;
 use dom::bindings::error::{Error, Fallible};
+use dom::bindings::nonnull::NonNullJSObjectPtr;
 use dom::bindings::reflector::{Reflector, reflect_dom_object};
 use dom::bindings::root::DomRoot;
 use dom::globalscope::GlobalScope;
@@ -44,7 +44,7 @@ impl CryptoMethods for Crypto {
     unsafe fn GetRandomValues(&self,
                        _cx: *mut JSContext,
                        input: *mut JSObject)
-                       -> Fallible<NonZero<*mut JSObject>> {
+                       -> Fallible<NonNullJSObjectPtr> {
         assert!(!input.is_null());
         typedarray!(in(_cx) let mut array_buffer_view: ArrayBufferView = input);
         let (array_type, mut data) = match array_buffer_view.as_mut() {
@@ -65,7 +65,7 @@ impl CryptoMethods for Crypto {
 
         self.rng.borrow_mut().fill_bytes(&mut data);
 
-        Ok(NonZero::new_unchecked(input))
+        Ok(NonNullJSObjectPtr::new_unchecked(input))
     }
 }
 
diff --git a/components/script/dom/document.rs b/components/script/dom/document.rs
index 1d8900ebb84..f4e734ceec5 100644
--- a/components/script/dom/document.rs
+++ b/components/script/dom/document.rs
@@ -3,7 +3,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use cookie_rs;
-use core::nonzero::NonZero;
 use devtools_traits::ScriptToDevtoolsControlMsg;
 use document_loader::{DocumentLoader, LoadType};
 use dom::activation::{ActivationSource, synthetic_click_activation};
@@ -24,6 +23,7 @@ use dom::bindings::codegen::Bindings::WindowBinding::{FrameRequestCallback, Scro
 use dom::bindings::codegen::UnionTypes::NodeOrString;
 use dom::bindings::error::{Error, ErrorResult, Fallible};
 use dom::bindings::inheritance::{Castable, ElementTypeId, HTMLElementTypeId, NodeTypeId};
+use dom::bindings::nonnull::NonNullJSObjectPtr;
 use dom::bindings::num::Finite;
 use dom::bindings::refcounted::{Trusted, TrustedPromise};
 use dom::bindings::reflector::{DomObject, reflect_dom_object};
@@ -99,7 +99,7 @@ use html5ever::{LocalName, Namespace, QualName};
 use hyper::header::{Header, SetCookie};
 use hyper_serde::Serde;
 use ipc_channel::ipc::{self, IpcSender};
-use js::jsapi::{JSContext, JSObject, JSRuntime};
+use js::jsapi::{JSContext, JSRuntime};
 use js::jsapi::JS_GetRuntime;
 use msg::constellation_msg::{ALT, CONTROL, SHIFT, SUPER};
 use msg::constellation_msg::{BrowsingContextId, Key, KeyModifiers, KeyState, TopLevelBrowsingContextId};
@@ -3536,7 +3536,7 @@ impl DocumentMethods for Document {
 
     #[allow(unsafe_code)]
     // https://html.spec.whatwg.org/multipage/#dom-tree-accessors:dom-document-nameditem-filter
-    unsafe fn NamedGetter(&self, _cx: *mut JSContext, name: DOMString) -> Option<NonZero<*mut JSObject>> {
+    unsafe fn NamedGetter(&self, _cx: *mut JSContext, name: DOMString) -> Option<NonNullJSObjectPtr> {
         #[derive(HeapSizeOf, JSTraceable)]
         struct NamedElementFilter {
             name: Atom,
@@ -3604,7 +3604,7 @@ impl DocumentMethods for Document {
                 if elements.peek().is_none() {
                     // TODO: Step 2.
                     // Step 3.
-                    return Some(NonZero::new_unchecked(first.reflector().get_jsobject().get()));
+                    return Some(NonNullJSObjectPtr::new_unchecked(first.reflector().get_jsobject().get()));
                 }
             } else {
                 return None;
@@ -3615,7 +3615,7 @@ impl DocumentMethods for Document {
             name: name,
         };
         let collection = HTMLCollection::create(self.window(), root, Box::new(filter));
-        Some(NonZero::new_unchecked(collection.reflector().get_jsobject().get()))
+        Some(NonNullJSObjectPtr::new_unchecked(collection.reflector().get_jsobject().get()))
     }
 
     // https://html.spec.whatwg.org/multipage/#dom-tree-accessors:supported-property-names
diff --git a/components/script/dom/gamepad.rs b/components/script/dom/gamepad.rs
index e5858309191..47605b7794e 100644
--- a/components/script/dom/gamepad.rs
+++ b/components/script/dom/gamepad.rs
@@ -2,10 +2,10 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-use core::nonzero::NonZero;
 use dom::bindings::codegen::Bindings::GamepadBinding;
 use dom::bindings::codegen::Bindings::GamepadBinding::GamepadMethods;
 use dom::bindings::inheritance::Castable;
+use dom::bindings::nonnull::NonNullJSObjectPtr;
 use dom::bindings::num::Finite;
 use dom::bindings::reflector::{DomObject, Reflector, reflect_dom_object};
 use dom::bindings::root::{Dom, DomRoot};
@@ -131,8 +131,8 @@ impl GamepadMethods for Gamepad {
 
     #[allow(unsafe_code)]
     // https://w3c.github.io/gamepad/#dom-gamepad-axes
-    unsafe fn Axes(&self, _cx: *mut JSContext) -> NonZero<*mut JSObject> {
-        NonZero::new_unchecked(self.axes.get())
+    unsafe fn Axes(&self, _cx: *mut JSContext) -> NonNullJSObjectPtr {
+        NonNullJSObjectPtr::new_unchecked(self.axes.get())
     }
 
     // https://w3c.github.io/gamepad/#dom-gamepad-buttons
diff --git a/components/script/dom/imagedata.rs b/components/script/dom/imagedata.rs
index e8ec2660c56..f0270fbe7b7 100644
--- a/components/script/dom/imagedata.rs
+++ b/components/script/dom/imagedata.rs
@@ -2,10 +2,10 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-use core::nonzero::NonZero;
 use dom::bindings::codegen::Bindings::ImageDataBinding;
 use dom::bindings::codegen::Bindings::ImageDataBinding::ImageDataMethods;
 use dom::bindings::error::{Fallible, Error};
+use dom::bindings::nonnull::NonNullJSObjectPtr;
 use dom::bindings::reflector::{Reflector, reflect_dom_object};
 use dom::bindings::root::DomRoot;
 use dom::globalscope::GlobalScope;
@@ -159,8 +159,8 @@ impl ImageDataMethods for ImageData {
 
     #[allow(unsafe_code)]
     // https://html.spec.whatwg.org/multipage/#dom-imagedata-data
-    unsafe fn Data(&self, _: *mut JSContext) -> NonZero<*mut JSObject> {
+    unsafe fn Data(&self, _: *mut JSContext) -> NonNullJSObjectPtr {
         assert!(!self.data.get().is_null());
-        NonZero::new_unchecked(self.data.get())
+        NonNullJSObjectPtr::new_unchecked(self.data.get())
     }
 }
diff --git a/components/script/dom/response.rs b/components/script/dom/response.rs
index c3224f17b7a..ee4276e711a 100644
--- a/components/script/dom/response.rs
+++ b/components/script/dom/response.rs
@@ -3,7 +3,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use body::{BodyOperations, BodyType, consume_body, consume_body_with_promise};
-use core::cell::Cell;
 use dom::bindings::cell::DomRefCell;
 use dom::bindings::codegen::Bindings::HeadersBinding::{HeadersInit, HeadersMethods};
 use dom::bindings::codegen::Bindings::ResponseBinding;
@@ -24,7 +23,7 @@ use hyper::status::StatusCode;
 use hyper_serde::Serde;
 use net_traits::response::{ResponseBody as NetTraitsResponseBody};
 use servo_url::ServoUrl;
-use std::cell::Ref;
+use std::cell::{Cell, Ref};
 use std::mem;
 use std::rc::Rc;
 use std::str::FromStr;
diff --git a/components/script/dom/testbinding.rs b/components/script/dom/testbinding.rs
index 620394e69dd..62738fcf379 100644
--- a/components/script/dom/testbinding.rs
+++ b/components/script/dom/testbinding.rs
@@ -4,7 +4,6 @@
 
 // check-tidy: no specs after this line
 
-use core::nonzero::NonZero;
 use dom::bindings::callback::ExceptionHandling;
 use dom::bindings::codegen::Bindings::EventListenerBinding::EventListener;
 use dom::bindings::codegen::Bindings::FunctionBinding::Function;
@@ -22,6 +21,7 @@ use dom::bindings::codegen::UnionTypes::{StringOrLongSequence, StringOrStringSeq
 use dom::bindings::codegen::UnionTypes::{StringOrUnsignedLong, StringOrBoolean, UnsignedLongOrBoolean};
 use dom::bindings::error::{Error, Fallible};
 use dom::bindings::mozmap::MozMap;
+use dom::bindings::nonnull::NonNullJSObjectPtr;
 use dom::bindings::num::Finite;
 use dom::bindings::refcounted::TrustedPromise;
 use dom::bindings::reflector::{DomObject, Reflector, reflect_dom_object};
@@ -151,20 +151,20 @@ impl TestBindingMethods for TestBinding {
     }
     fn SetUnion9Attribute(&self, _: ByteStringOrLong) {}
     #[allow(unsafe_code)]
-    unsafe fn ArrayAttribute(&self, cx: *mut JSContext) -> NonZero<*mut JSObject> {
+    unsafe fn ArrayAttribute(&self, cx: *mut JSContext) -> NonNullJSObjectPtr {
         rooted!(in(cx) let array = JS_NewUint8ClampedArray(cx, 16));
         assert!(!array.is_null());
-        NonZero::new_unchecked(array.get())
+        NonNullJSObjectPtr::new_unchecked(array.get())
     }
     #[allow(unsafe_code)]
     unsafe fn AnyAttribute(&self, _: *mut JSContext) -> JSVal { NullValue() }
     #[allow(unsafe_code)]
     unsafe fn SetAnyAttribute(&self, _: *mut JSContext, _: HandleValue) {}
     #[allow(unsafe_code)]
-    unsafe fn ObjectAttribute(&self, cx: *mut JSContext) -> NonZero<*mut JSObject> {
+    unsafe fn ObjectAttribute(&self, cx: *mut JSContext) -> NonNullJSObjectPtr {
         rooted!(in(cx) let obj = JS_NewPlainObject(cx));
         assert!(!obj.is_null());
-        NonZero::new_unchecked(obj.get())
+        NonNullJSObjectPtr::new_unchecked(obj.get())
     }
     #[allow(unsafe_code)]
     unsafe fn SetObjectAttribute(&self, _: *mut JSContext, _: *mut JSObject) {}
@@ -220,7 +220,7 @@ impl TestBindingMethods for TestBinding {
         self.url.set(url);
     }
     #[allow(unsafe_code)]
-    unsafe fn GetObjectAttributeNullable(&self, _: *mut JSContext) -> Option<NonZero<*mut JSObject>> { None }
+    unsafe fn GetObjectAttributeNullable(&self, _: *mut JSContext) -> Option<NonNullJSObjectPtr> { None }
     #[allow(unsafe_code)]
     unsafe fn SetObjectAttributeNullable(&self, _: *mut JSContext, _: *mut JSObject) {}
     fn GetUnionAttributeNullable(&self) -> Option<HTMLElementOrLong> {
@@ -272,7 +272,7 @@ impl TestBindingMethods for TestBinding {
     #[allow(unsafe_code)]
     unsafe fn ReceiveAny(&self, _: *mut JSContext) -> JSVal { NullValue() }
     #[allow(unsafe_code)]
-    unsafe fn ReceiveObject(&self, cx: *mut JSContext) -> NonZero<*mut JSObject> {
+    unsafe fn ReceiveObject(&self, cx: *mut JSContext) -> NonNullJSObjectPtr {
         self.ObjectAttribute(cx)
     }
     fn ReceiveUnion(&self) -> HTMLElementOrLong { HTMLElementOrLong::Long(0) }
@@ -316,7 +316,7 @@ impl TestBindingMethods for TestBinding {
         Some(Blob::new(&self.global(), BlobImpl::new_from_bytes(vec![]), "".to_owned()))
     }
     #[allow(unsafe_code)]
-    unsafe fn ReceiveNullableObject(&self, cx: *mut JSContext) -> Option<NonZero<*mut JSObject>> {
+    unsafe fn ReceiveNullableObject(&self, cx: *mut JSContext) -> Option<NonNullJSObjectPtr> {
         self.GetObjectAttributeNullable(cx)
     }
     fn ReceiveNullableUnion(&self) -> Option<HTMLElementOrLong> {
diff --git a/components/script/dom/textencoder.rs b/components/script/dom/textencoder.rs
index 78ccbfcae0b..7ca2a429525 100644
--- a/components/script/dom/textencoder.rs
+++ b/components/script/dom/textencoder.rs
@@ -2,16 +2,16 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-use core::nonzero::NonZero;
 use dom::bindings::codegen::Bindings::TextEncoderBinding;
 use dom::bindings::codegen::Bindings::TextEncoderBinding::TextEncoderMethods;
 use dom::bindings::error::Fallible;
+use dom::bindings::nonnull::NonNullJSObjectPtr;
 use dom::bindings::reflector::{Reflector, reflect_dom_object};
 use dom::bindings::root::DomRoot;
 use dom::bindings::str::{DOMString, USVString};
 use dom::globalscope::GlobalScope;
 use dom_struct::dom_struct;
-use js::jsapi::{JSContext, JSObject};
+use js::jsapi::JSContext;
 use js::typedarray::{Uint8Array, CreateWith};
 use std::ptr;
 
@@ -47,12 +47,12 @@ impl TextEncoderMethods for TextEncoder {
 
     #[allow(unsafe_code)]
     // https://encoding.spec.whatwg.org/#dom-textencoder-encode
-    unsafe fn Encode(&self, cx: *mut JSContext, input: USVString) -> NonZero<*mut JSObject> {
+    unsafe fn Encode(&self, cx: *mut JSContext, input: USVString) -> NonNullJSObjectPtr {
         let encoded = input.0.as_bytes();
 
         rooted!(in(cx) let mut js_object = ptr::null_mut());
         assert!(Uint8Array::create(cx, CreateWith::Slice(&encoded), js_object.handle_mut()).is_ok());
 
-        NonZero::new_unchecked(js_object.get())
+        NonNullJSObjectPtr::new_unchecked(js_object.get())
     }
 }
diff --git a/components/script/dom/vrdisplay.rs b/components/script/dom/vrdisplay.rs
index bc334ae01e4..4f012856c2c 100644
--- a/components/script/dom/vrdisplay.rs
+++ b/components/script/dom/vrdisplay.rs
@@ -3,7 +3,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use canvas_traits::webgl::{webgl_channel, WebGLReceiver, WebVRCommand};
-use core::ops::Deref;
 use dom::bindings::callback::ExceptionHandling;
 use dom::bindings::cell::DomRefCell;
 use dom::bindings::codegen::Bindings::PerformanceBinding::PerformanceBinding::PerformanceMethods;
@@ -38,6 +37,7 @@ use script_runtime::CommonScriptMsg;
 use script_runtime::ScriptThreadEventCategory::WebVREvent;
 use std::cell::Cell;
 use std::mem;
+use std::ops::Deref;
 use std::rc::Rc;
 use std::sync::mpsc;
 use std::thread;
diff --git a/components/script/dom/vreyeparameters.rs b/components/script/dom/vreyeparameters.rs
index 2483a63e170..f29d0230de5 100644
--- a/components/script/dom/vreyeparameters.rs
+++ b/components/script/dom/vreyeparameters.rs
@@ -2,10 +2,10 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-use core::nonzero::NonZero;
 use dom::bindings::cell::DomRefCell;
 use dom::bindings::codegen::Bindings::VREyeParametersBinding;
 use dom::bindings::codegen::Bindings::VREyeParametersBinding::VREyeParametersMethods;
+use dom::bindings::nonnull::NonNullJSObjectPtr;
 use dom::bindings::reflector::{Reflector, reflect_dom_object};
 use dom::bindings::root::{Dom, DomRoot};
 use dom::globalscope::GlobalScope;
@@ -60,8 +60,8 @@ impl VREyeParameters {
 impl VREyeParametersMethods for VREyeParameters {
     #[allow(unsafe_code)]
     // https://w3c.github.io/webvr/#dom-vreyeparameters-offset
-    unsafe fn Offset(&self, _cx: *mut JSContext) -> NonZero<*mut JSObject> {
-        NonZero::new_unchecked(self.offset.get())
+    unsafe fn Offset(&self, _cx: *mut JSContext) -> NonNullJSObjectPtr {
+        NonNullJSObjectPtr::new_unchecked(self.offset.get())
     }
 
     // https://w3c.github.io/webvr/#dom-vreyeparameters-fieldofview
diff --git a/components/script/dom/vrframedata.rs b/components/script/dom/vrframedata.rs
index fc7d3dee494..0c36536e4b7 100644
--- a/components/script/dom/vrframedata.rs
+++ b/components/script/dom/vrframedata.rs
@@ -2,10 +2,10 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-use core::nonzero::NonZero;
 use dom::bindings::codegen::Bindings::VRFrameDataBinding;
 use dom::bindings::codegen::Bindings::VRFrameDataBinding::VRFrameDataMethods;
 use dom::bindings::error::Fallible;
+use dom::bindings::nonnull::NonNullJSObjectPtr;
 use dom::bindings::num::Finite;
 use dom::bindings::reflector::{DomObject, Reflector, reflect_dom_object};
 use dom::bindings::root::{Dom, DomRoot};
@@ -118,26 +118,26 @@ impl VRFrameDataMethods for VRFrameData {
 
     #[allow(unsafe_code)]
     // https://w3c.github.io/webvr/#dom-vrframedata-leftprojectionmatrix
-    unsafe fn LeftProjectionMatrix(&self, _cx: *mut JSContext) -> NonZero<*mut JSObject> {
-        NonZero::new_unchecked(self.left_proj.get())
+    unsafe fn LeftProjectionMatrix(&self, _cx: *mut JSContext) -> NonNullJSObjectPtr {
+        NonNullJSObjectPtr::new_unchecked(self.left_proj.get())
     }
 
     #[allow(unsafe_code)]
     // https://w3c.github.io/webvr/#dom-vrframedata-leftviewmatrix
-    unsafe fn LeftViewMatrix(&self, _cx: *mut JSContext) -> NonZero<*mut JSObject> {
-        NonZero::new_unchecked(self.left_view.get())
+    unsafe fn LeftViewMatrix(&self, _cx: *mut JSContext) -> NonNullJSObjectPtr {
+        NonNullJSObjectPtr::new_unchecked(self.left_view.get())
     }
 
     #[allow(unsafe_code)]
     // https://w3c.github.io/webvr/#dom-vrframedata-rightprojectionmatrix
-    unsafe fn RightProjectionMatrix(&self, _cx: *mut JSContext) -> NonZero<*mut JSObject> {
-        NonZero::new_unchecked(self.right_proj.get())
+    unsafe fn RightProjectionMatrix(&self, _cx: *mut JSContext) -> NonNullJSObjectPtr {
+        NonNullJSObjectPtr::new_unchecked(self.right_proj.get())
     }
 
     #[allow(unsafe_code)]
     // https://w3c.github.io/webvr/#dom-vrframedata-rightviewmatrix
-    unsafe fn RightViewMatrix(&self, _cx: *mut JSContext) -> NonZero<*mut JSObject> {
-        NonZero::new_unchecked(self.right_view.get())
+    unsafe fn RightViewMatrix(&self, _cx: *mut JSContext) -> NonNullJSObjectPtr {
+        NonNullJSObjectPtr::new_unchecked(self.right_view.get())
     }
 
     // https://w3c.github.io/webvr/#dom-vrframedata-pose
diff --git a/components/script/dom/vrpose.rs b/components/script/dom/vrpose.rs
index 816929aa5c6..b6a9fad10a0 100644
--- a/components/script/dom/vrpose.rs
+++ b/components/script/dom/vrpose.rs
@@ -2,9 +2,9 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-use core::nonzero::NonZero;
 use dom::bindings::codegen::Bindings::VRPoseBinding;
 use dom::bindings::codegen::Bindings::VRPoseBinding::VRPoseMethods;
+use dom::bindings::nonnull::NonNullJSObjectPtr;
 use dom::bindings::reflector::{DomObject, Reflector, reflect_dom_object};
 use dom::bindings::root::DomRoot;
 use dom::globalscope::GlobalScope;
@@ -52,13 +52,13 @@ unsafe fn update_or_create_typed_array(cx: *mut JSContext,
 
 #[inline]
 #[allow(unsafe_code)]
-fn heap_to_option(heap: &Heap<*mut JSObject>) -> Option<NonZero<*mut JSObject>> {
+fn heap_to_option(heap: &Heap<*mut JSObject>) -> Option<NonNullJSObjectPtr> {
     let js_object = heap.get();
     if js_object.is_null() {
         None
     } else {
         unsafe {
-            Some(NonZero::new_unchecked(js_object))
+            Some(NonNullJSObjectPtr::new_unchecked(js_object))
         }
     }
 }
@@ -101,37 +101,37 @@ impl VRPose {
 impl VRPoseMethods for VRPose {
     #[allow(unsafe_code)]
     // https://w3c.github.io/webvr/#dom-vrpose-position
-    unsafe fn GetPosition(&self, _cx: *mut JSContext) -> Option<NonZero<*mut JSObject>> {
+    unsafe fn GetPosition(&self, _cx: *mut JSContext) -> Option<NonNullJSObjectPtr> {
         heap_to_option(&self.position)
     }
 
     #[allow(unsafe_code)]
     // https://w3c.github.io/webvr/#dom-vrpose-linearvelocity
-    unsafe fn GetLinearVelocity(&self, _cx: *mut JSContext) -> Option<NonZero<*mut JSObject>> {
+    unsafe fn GetLinearVelocity(&self, _cx: *mut JSContext) -> Option<NonNullJSObjectPtr> {
         heap_to_option(&self.linear_vel)
     }
 
     #[allow(unsafe_code)]
     // https://w3c.github.io/webvr/#dom-vrpose-linearacceleration
-    unsafe fn GetLinearAcceleration(&self, _cx: *mut JSContext) -> Option<NonZero<*mut JSObject>> {
+    unsafe fn GetLinearAcceleration(&self, _cx: *mut JSContext) -> Option<NonNullJSObjectPtr> {
         heap_to_option(&self.linear_acc)
     }
 
     #[allow(unsafe_code)]
     // https://w3c.github.io/webvr/#dom-vrpose-orientation
-    unsafe fn GetOrientation(&self, _cx: *mut JSContext) -> Option<NonZero<*mut JSObject>> {
+    unsafe fn GetOrientation(&self, _cx: *mut JSContext) -> Option<NonNullJSObjectPtr> {
         heap_to_option(&self.orientation)
     }
 
     #[allow(unsafe_code)]
     // https://w3c.github.io/webvr/#dom-vrpose-angularvelocity
-    unsafe fn GetAngularVelocity(&self, _cx: *mut JSContext) -> Option<NonZero<*mut JSObject>> {
+    unsafe fn GetAngularVelocity(&self, _cx: *mut JSContext) -> Option<NonNullJSObjectPtr> {
         heap_to_option(&self.angular_vel)
     }
 
     #[allow(unsafe_code)]
     // https://w3c.github.io/webvr/#dom-vrpose-angularacceleration
-    unsafe fn GetAngularAcceleration(&self, _cx: *mut JSContext) -> Option<NonZero<*mut JSObject>> {
+    unsafe fn GetAngularAcceleration(&self, _cx: *mut JSContext) -> Option<NonNullJSObjectPtr> {
         heap_to_option(&self.angular_acc)
     }
 }
diff --git a/components/script/dom/vrstageparameters.rs b/components/script/dom/vrstageparameters.rs
index 8996f0fdbad..a2a185fd6cc 100644
--- a/components/script/dom/vrstageparameters.rs
+++ b/components/script/dom/vrstageparameters.rs
@@ -2,10 +2,10 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-use core::nonzero::NonZero;
 use dom::bindings::cell::DomRefCell;
 use dom::bindings::codegen::Bindings::VRStageParametersBinding;
 use dom::bindings::codegen::Bindings::VRStageParametersBinding::VRStageParametersMethods;
+use dom::bindings::nonnull::NonNullJSObjectPtr;
 use dom::bindings::num::Finite;
 use dom::bindings::reflector::{DomObject, Reflector, reflect_dom_object};
 use dom::bindings::root::DomRoot;
@@ -69,8 +69,8 @@ impl VRStageParameters {
 impl VRStageParametersMethods for VRStageParameters {
     #[allow(unsafe_code)]
     // https://w3c.github.io/webvr/#dom-vrstageparameters-sittingtostandingtransform
-    unsafe fn SittingToStandingTransform(&self, _cx: *mut JSContext) -> NonZero<*mut JSObject> {
-        NonZero::new_unchecked(self.transform.get())
+    unsafe fn SittingToStandingTransform(&self, _cx: *mut JSContext) -> NonNullJSObjectPtr {
+        NonNullJSObjectPtr::new_unchecked(self.transform.get())
     }
 
     // https://w3c.github.io/webvr/#dom-vrstageparameters-sizex
diff --git a/components/script/dom/webgl_extensions/ext/webglvertexarrayobjectoes.rs b/components/script/dom/webgl_extensions/ext/webglvertexarrayobjectoes.rs
index 70ed5a6f778..4ca8c7b7add 100644
--- a/components/script/dom/webgl_extensions/ext/webglvertexarrayobjectoes.rs
+++ b/components/script/dom/webgl_extensions/ext/webglvertexarrayobjectoes.rs
@@ -3,8 +3,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use canvas_traits::webgl::WebGLVertexArrayId;
-use core::cell::Ref;
-use core::iter::FromIterator;
 use dom::bindings::cell::DomRefCell;
 use dom::bindings::codegen::Bindings::WebGLVertexArrayObjectOESBinding;
 use dom::bindings::reflector::reflect_dom_object;
@@ -13,8 +11,9 @@ use dom::globalscope::GlobalScope;
 use dom::webglbuffer::WebGLBuffer;
 use dom::webglobject::WebGLObject;
 use dom_struct::dom_struct;
-use std::cell::Cell;
+use std::cell::{Cell, Ref};
 use std::collections::HashMap;
+use std::iter::FromIterator;
 
 #[dom_struct]
 pub struct WebGLVertexArrayObjectOES {
diff --git a/components/script/dom/webgl_extensions/extensions.rs b/components/script/dom/webgl_extensions/extensions.rs
index 7cb478f9fb0..9b022ac7def 100644
--- a/components/script/dom/webgl_extensions/extensions.rs
+++ b/components/script/dom/webgl_extensions/extensions.rs
@@ -3,23 +3,23 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 use canvas_traits::webgl::WebGLError;
-use core::iter::FromIterator;
-use core::nonzero::NonZero;
 use dom::bindings::cell::DomRefCell;
 use dom::bindings::codegen::Bindings::OESStandardDerivativesBinding::OESStandardDerivativesConstants;
 use dom::bindings::codegen::Bindings::OESTextureHalfFloatBinding::OESTextureHalfFloatConstants;
 use dom::bindings::codegen::Bindings::WebGLRenderingContextBinding::WebGLRenderingContextConstants as constants;
+use dom::bindings::nonnull::NonNullJSObjectPtr;
 use dom::bindings::root::DomRoot;
 use dom::bindings::trace::JSTraceable;
 use dom::webglrenderingcontext::WebGLRenderingContext;
 use fnv::{FnvHashMap, FnvHashSet};
 use gleam::gl::GLenum;
 use heapsize::HeapSizeOf;
-use js::jsapi::{JSContext, JSObject};
+use js::jsapi::JSContext;
 use js::jsval::JSVal;
 use ref_filter_map::ref_filter_map;
 use std::cell::Ref;
 use std::collections::HashMap;
+use std::iter::FromIterator;
 use super::{ext, WebGLExtension};
 use super::wrapper::{WebGLExtensionWrapper, TypedWebGLExtensionWrapper};
 
@@ -109,7 +109,7 @@ impl WebGLExtensions {
                                 .collect()
     }
 
-    pub fn get_or_init_extension(&self, name: &str, ctx: &WebGLRenderingContext) -> Option<NonZero<*mut JSObject>> {
+    pub fn get_or_init_extension(&self, name: &str, ctx: &WebGLRenderingContext) -> Option<NonNullJSObjectPtr> {
         let name = name.to_uppercase();
         self.extensions.borrow().get(&name).and_then(|extension| {
             if extension.is_supported(self) {
diff --git a/components/script/dom/webgl_extensions/wrapper.rs b/components/script/dom/webgl_extensions/wrapper.rs
index 7b4452ad7dc..49d698bf14c 100644
--- a/components/script/dom/webgl_extensions/wrapper.rs
+++ b/components/script/dom/webgl_extensions/wrapper.rs
@@ -2,13 +2,12 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-use core::nonzero::NonZero;
+use dom::bindings::nonnull::NonNullJSObjectPtr;
 use dom::bindings::reflector::DomObject;
 use dom::bindings::root::{DomRoot, MutNullableDom};
 use dom::bindings::trace::JSTraceable;
 use dom::webglrenderingcontext::WebGLRenderingContext;
 use heapsize::HeapSizeOf;
-use js::jsapi::JSObject;
 use std::any::Any;
 use super::{WebGLExtension, WebGLExtensions};
 
@@ -18,7 +17,7 @@ pub trait WebGLExtensionWrapper: JSTraceable + HeapSizeOf {
     fn instance_or_init(&self,
                         ctx: &WebGLRenderingContext,
                         ext: &WebGLExtensions)
-                        -> NonZero<*mut JSObject>;
+                        -> NonNullJSObjectPtr;
     fn is_supported(&self, &WebGLExtensions) -> bool;
     fn is_enabled(&self) -> bool;
     fn enable(&self, ext: &WebGLExtensions);
@@ -48,7 +47,7 @@ impl<T> WebGLExtensionWrapper for TypedWebGLExtensionWrapper<T>
     fn instance_or_init(&self,
                         ctx: &WebGLRenderingContext,
                         ext: &WebGLExtensions)
-                        -> NonZero<*mut JSObject> {
+                        -> NonNullJSObjectPtr {
         let mut enabled = true;
         let extension = self.extension.or_init(|| {
             enabled = false;
@@ -58,7 +57,7 @@ impl<T> WebGLExtensionWrapper for TypedWebGLExtensionWrapper<T>
             self.enable(ext);
         }
         unsafe {
-            NonZero::new_unchecked(extension.reflector().get_jsobject().get())
+            NonNullJSObjectPtr::new_unchecked(extension.reflector().get_jsobject().get())
         }
     }
 
diff --git a/components/script/dom/webglrenderingcontext.rs b/components/script/dom/webglrenderingcontext.rs
index d4624d3eb85..98076fa4889 100644
--- a/components/script/dom/webglrenderingcontext.rs
+++ b/components/script/dom/webglrenderingcontext.rs
@@ -9,9 +9,6 @@ use canvas_traits::webgl::{WebGLFramebufferBindingRequest, WebGLMsg, WebGLMsgSen
 use canvas_traits::webgl::DOMToTextureCommand;
 use canvas_traits::webgl::WebGLError::*;
 use canvas_traits::webgl::webgl_channel;
-use core::cell::Ref;
-use core::iter::FromIterator;
-use core::nonzero::NonZero;
 use dom::bindings::cell::DomRefCell;
 use dom::bindings::codegen::Bindings::WebGLRenderingContextBinding::{self, WebGLContextAttributes};
 use dom::bindings::codegen::Bindings::WebGLRenderingContextBinding::WebGLRenderingContextConstants as constants;
@@ -20,6 +17,7 @@ use dom::bindings::codegen::UnionTypes::ImageDataOrHTMLImageElementOrHTMLCanvasE
 use dom::bindings::conversions::{ConversionResult, FromJSValConvertible, ToJSValConvertible};
 use dom::bindings::error::{Error, Fallible};
 use dom::bindings::inheritance::Castable;
+use dom::bindings::nonnull::NonNullJSObjectPtr;
 use dom::bindings::reflector::{DomObject, Reflector, reflect_dom_object};
 use dom::bindings::root::{Dom, DomRoot, LayoutDom, MutNullableDom};
 use dom::bindings::str::DOMString;
@@ -57,7 +55,8 @@ use net_traits::image_cache::ImageResponse;
 use offscreen_gl_context::{GLContextAttributes, GLLimits};
 use script_layout_interface::HTMLCanvasDataSource;
 use servo_config::prefs::PREFS;
-use std::cell::Cell;
+use std::cell::{Cell, Ref};
+use std::iter::FromIterator;
 use webrender_api;
 
 type ImagePixelResult = Result<(Vec<u8>, Size2D<i32>, bool), ()>;
@@ -1379,7 +1378,7 @@ impl WebGLRenderingContextMethods for WebGLRenderingContext {
     #[allow(unsafe_code)]
     // https://www.khronos.org/registry/webgl/specs/latest/1.0/#5.14.14
     unsafe fn GetExtension(&self, _cx: *mut JSContext, name: DOMString)
-                    -> Option<NonZero<*mut JSObject>> {
+                    -> Option<NonNullJSObjectPtr> {
         self.extension_manager.init_once(|| {
             self.get_gl_extensions()
         });
diff --git a/components/script/dom/window.rs b/components/script/dom/window.rs
index 047cc1678ea..1f8e3282064 100644
--- a/components/script/dom/window.rs
+++ b/components/script/dom/window.rs
@@ -808,6 +808,7 @@ impl WindowMethods for Window {
 
     #[allow(unsafe_code)]
     fn Trap(&self) {
+        #[cfg(feature = "unstable")]
         unsafe { ::std::intrinsics::breakpoint() }
     }
 
diff --git a/components/script/dom/xmldocument.rs b/components/script/dom/xmldocument.rs
index a74cb88af6b..acbdea33582 100644
--- a/components/script/dom/xmldocument.rs
+++ b/components/script/dom/xmldocument.rs
@@ -2,11 +2,11 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-use core::nonzero::NonZero;
 use document_loader::DocumentLoader;
 use dom::bindings::codegen::Bindings::DocumentBinding::DocumentMethods;
 use dom::bindings::codegen::Bindings::XMLDocumentBinding::{self, XMLDocumentMethods};
 use dom::bindings::inheritance::Castable;
+use dom::bindings::nonnull::NonNullJSObjectPtr;
 use dom::bindings::reflector::reflect_dom_object;
 use dom::bindings::root::DomRoot;
 use dom::bindings::str::DOMString;
@@ -15,7 +15,7 @@ use dom::location::Location;
 use dom::node::Node;
 use dom::window::Window;
 use dom_struct::dom_struct;
-use js::jsapi::{JSContext, JSObject};
+use js::jsapi::JSContext;
 use script_traits::DocumentActivity;
 use servo_url::{MutableOrigin, ServoUrl};
 
@@ -100,7 +100,7 @@ impl XMLDocumentMethods for XMLDocument {
 
     #[allow(unsafe_code)]
     // https://html.spec.whatwg.org/multipage/#dom-tree-accessors:dom-document-nameditem-filter
-    unsafe fn NamedGetter(&self, _cx: *mut JSContext, name: DOMString) -> Option<NonZero<*mut JSObject>> {
+    unsafe fn NamedGetter(&self, _cx: *mut JSContext, name: DOMString) -> Option<NonNullJSObjectPtr> {
         self.upcast::<Document>().NamedGetter(_cx, name)
     }
 }
diff --git a/components/script/lib.rs b/components/script/lib.rs
index 8922aa37e62..5f33f1e1151 100644
--- a/components/script/lib.rs
+++ b/components/script/lib.rs
@@ -2,14 +2,11 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
+#![cfg_attr(feature = "unstable", feature(core_intrinsics))]
+#![cfg_attr(feature = "unstable", feature(on_unimplemented))]
 #![feature(conservative_impl_trait)]
 #![feature(const_fn)]
-#![feature(const_ptr_null)]
-#![feature(const_ptr_null_mut)]
-#![feature(core_intrinsics)]
 #![feature(mpsc_select)]
-#![feature(nonzero)]
-#![feature(on_unimplemented)]
 #![feature(plugin)]
 #![feature(proc_macro)]
 
@@ -31,7 +28,6 @@ extern crate byteorder;
 extern crate canvas_traits;
 extern crate caseless;
 extern crate cookie as cookie_rs;
-extern crate core;
 #[macro_use] extern crate cssparser;
 #[macro_use] extern crate deny_public_fields;
 extern crate devtools_traits;
@@ -67,6 +63,7 @@ extern crate mime_guess;
 extern crate mitochondria;
 extern crate msg;
 extern crate net_traits;
+extern crate nonzero;
 extern crate num_traits;
 extern crate offscreen_gl_context;
 extern crate open;
diff --git a/components/script/task.rs b/components/script/task.rs
index e90fc21c55c..eab786c8c20 100644
--- a/components/script/task.rs
+++ b/components/script/task.rs
@@ -5,7 +5,6 @@
 //! Machinery for [tasks](https://html.spec.whatwg.org/multipage/#concept-task).
 
 use std::fmt;
-use std::intrinsics;
 use std::sync::Arc;
 use std::sync::atomic::{AtomicBool, Ordering};
 
@@ -33,7 +32,10 @@ macro_rules! task {
 pub trait TaskOnce: Send {
     #[allow(unsafe_code)]
     fn name(&self) -> &'static str {
-        unsafe { intrinsics::type_name::<Self>() }
+        #[cfg(feature = "unstable")]
+        unsafe { ::std::intrinsics::type_name::<Self>() }
+        #[cfg(not(feature = "unstable"))]
+        { "(task name unknown)" }
     }
 
     fn run_once(self);
diff --git a/components/script_layout_interface/lib.rs b/components/script_layout_interface/lib.rs
index 7b45d9688f1..0216ca84543 100644
--- a/components/script_layout_interface/lib.rs
+++ b/components/script_layout_interface/lib.rs
@@ -45,10 +45,9 @@ use canvas_traits::canvas::CanvasMsg;
 use ipc_channel::ipc::IpcSender;
 use libc::c_void;
 use net_traits::image_cache::PendingImageId;
-use nonzero::NonZeroUsize;
+use nonzero::NonZero;
 use script_traits::UntrustedNodeAddress;
 use servo_url::ServoUrl;
-use std::marker::PhantomData;
 use std::sync::atomic::AtomicIsize;
 use style::data::ElementData;
 
@@ -78,8 +77,7 @@ pub struct OpaqueStyleAndLayoutData {
     // NB: We really store a `StyleAndLayoutData` here, so be careful!
     #[ignore_heap_size_of = "TODO(#6910) Box value that should be counted but \
                              the type lives in layout"]
-    pub ptr: NonZeroUsize,
-    pub phantom: PhantomData<*mut StyleData>,
+    pub ptr: NonZero<*mut StyleData>,
 }
 
 #[allow(unsafe_code)]
diff --git a/components/servo/Cargo.toml b/components/servo/Cargo.toml
index 70e1a6c9000..9149a2918b1 100644
--- a/components/servo/Cargo.toml
+++ b/components/servo/Cargo.toml
@@ -23,6 +23,7 @@ unstable = [
     "gfx/unstable",
     "msg/unstable",
     "profile/unstable",
+    "script/unstable",
 ]
 
 [dependencies]
diff --git a/etc/ci/buildbot_steps.yml b/etc/ci/buildbot_steps.yml
index 317077c0287..09438dce966 100644
--- a/etc/ci/buildbot_steps.yml
+++ b/etc/ci/buildbot_steps.yml
@@ -84,6 +84,7 @@ linux-dev:
   - env SERVO_RUSTC_LLVM_ASSERTIONS=1 ./mach test-unit
   - env SERVO_RUSTC_LLVM_ASSERTIONS=1 ./mach package --dev
   - env SERVO_RUSTC_LLVM_ASSERTIONS=1 ./mach build-cef
+  - env SERVO_RUSTC_LLVM_ASSERTIONS=1 ./mach build --dev --no-default-features --features default-except-unstable
   - ./mach build-geckolib
   - ./mach test-stylo
   - bash ./etc/ci/lockfile_changed.sh
diff --git a/ports/servo/main.rs b/ports/servo/main.rs
index 19063d1176a..b24737f2d19 100644
--- a/ports/servo/main.rs
+++ b/ports/servo/main.rs
@@ -15,7 +15,7 @@
 //!
 //! [glutin]: https://github.com/tomaka/glutin
 
-#![feature(core_intrinsics)]
+#![cfg_attr(feature = "unstable", feature(core_intrinsics))]
 
 #[cfg(target_os = "android")]
 extern crate android_injected_glue;
@@ -26,7 +26,7 @@ extern crate glutin_app as app;
 extern crate log;
 // The Servo engine
 extern crate servo;
-#[cfg(not(target_os = "android"))]
+#[cfg(all(feature = "unstable", not(target_os = "android")))]
 #[macro_use]
 extern crate sig;
 
@@ -57,7 +57,7 @@ pub mod platform {
     pub fn deinit() {}
 }
 
-#[cfg(not(target_os = "android"))]
+#[cfg(all(feature = "unstable", not(target_os = "android")))]
 fn install_crash_handler() {
     use backtrace::Backtrace;
     use sig::ffi::Sig;
@@ -83,7 +83,7 @@ fn install_crash_handler() {
     signal!(Sig::BUS, handler); // handle invalid memory access
 }
 
-#[cfg(target_os = "android")]
+#[cfg(any(not(feature = "unstable"), target_os = "android"))]
 fn install_crash_handler() {}
 
 fn main() {
diff --git a/tests/unit/style/lib.rs b/tests/unit/style/lib.rs
index c1eab17d1b6..98ed3a9edd6 100644
--- a/tests/unit/style/lib.rs
+++ b/tests/unit/style/lib.rs
@@ -3,7 +3,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #![cfg(test)]
-#![feature(plugin, test)]
+#![feature(test)]
 
 extern crate app_units;
 extern crate cssparser;