Make it possible to build the style_traits crate with a stable compiler.

Testing this on CI to make sure we don’t regress it is blocked on #11806

20 files changed, 145 insertions, 89 deletions

diff --git a/components/gfx/Cargo.toml b/components/gfx/Cargo.toml
index 4a5dcba9a28..83ab6b25a91 100644
--- a/components/gfx/Cargo.toml
+++ b/components/gfx/Cargo.toml
@@ -13,7 +13,7 @@ path = "lib.rs"
 app_units = {version = "0.2.3", features = ["plugins"]}
 azure = {git = "https://github.com/servo/rust-azure", features = ["plugins"]}
 bitflags = "0.7"
-euclid = {version = "0.6.4", features = ["plugins"]}
+euclid = {version = "0.6.4", features = ["plugins", "unstable"]}
 fnv = "1.0"
 gfx_traits = {path = "../gfx_traits"}
 harfbuzz-sys = "0.1"
diff --git a/components/gfx/display_list/mod.rs b/components/gfx/display_list/mod.rs
index 1ec5aaf0d14..ac93adcca1f 100644
--- a/components/gfx/display_list/mod.rs
+++ b/components/gfx/display_list/mod.rs
@@ -20,7 +20,8 @@ use azure::azure_hl::Color;
 use euclid::approxeq::ApproxEq;
 use euclid::num::Zero;
 use euclid::rect::TypedRect;
-use euclid::{Matrix2D, Matrix4D, Point2D, Rect, SideOffsets2D, Size2D};
+use euclid::side_offsets::SideOffsets2D;
+use euclid::{Matrix2D, Matrix4D, Point2D, Rect, Size2D};
 use fnv::FnvHasher;
 use gfx_traits::{LayerId, ScrollPolicy, StackingContextId};
 use ipc_channel::ipc::IpcSharedMemory;
diff --git a/components/msg/Cargo.toml b/components/msg/Cargo.toml
index 13e2ae8f863..ac3a967802d 100644
--- a/components/msg/Cargo.toml
+++ b/components/msg/Cargo.toml
@@ -21,6 +21,6 @@ plugins = {path = "../plugins"}
 rustc-serialize = "0.3.4"
 serde = "0.7"
 serde_macros = "0.7"
-url = {version = "1.0.0", features = ["heap_size"]}
-util = {path = "../util"}
+url = {version = "1.0.0", features = ["heap_size", "serde"]}
+util = {path = "../util", features = ["servo"]}
 webrender_traits = {git = "https://github.com/servo/webrender_traits"}
diff --git a/components/profile/Cargo.toml b/components/profile/Cargo.toml
index ad7ab35a9d8..da8d01ca514 100644
--- a/components/profile/Cargo.toml
+++ b/components/profile/Cargo.toml
@@ -11,7 +11,7 @@ path = "lib.rs"
 [dependencies]
 profile_traits = {path = "../profile_traits"}
 plugins = {path = "../plugins"}
-util = {path = "../util"}
+util = {path = "../util", features = ["servo"]}
 ipc-channel = {git = "https://github.com/servo/ipc-channel"}
 heartbeats-simple = "0.3"
 log = "0.3.5"
diff --git a/components/script_traits/Cargo.toml b/components/script_traits/Cargo.toml
index 39755274168..f1e21ca27b6 100644
--- a/components/script_traits/Cargo.toml
+++ b/components/script_traits/Cargo.toml
@@ -15,7 +15,7 @@ msg = {path = "../msg"}
 net_traits = {path = "../net_traits"}
 plugins = {path = "../plugins"}
 profile_traits = {path = "../profile_traits"}
-style_traits = {path = "../style_traits"}
+style_traits = {path = "../style_traits", features = ["serde-serialization"]}
 util = {path = "../util"}
 devtools_traits = {path = "../devtools_traits"}
 ipc-channel = {git = "https://github.com/servo/ipc-channel"}
diff --git a/components/servo/Cargo.lock b/components/servo/Cargo.lock
index 10b36f51793..872f9dddaaf 100644
--- a/components/servo/Cargo.lock
+++ b/components/servo/Cargo.lock
@@ -2253,7 +2253,6 @@ dependencies = [
  "euclid 0.6.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "heapsize 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "heapsize_plugin 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
- "plugins 0.0.1",
  "rustc-serialize 0.3.19 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde 0.7.10 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_macros 0.7.10 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2438,7 +2437,6 @@ dependencies = [
  "euclid 0.6.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "getopts 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)",
  "heapsize 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
- "heapsize_plugin 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "ipc-channel 0.2.3 (git+https://github.com/servo/ipc-channel)",
  "kernel32-sys 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "lazy_static 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2446,7 +2444,6 @@ dependencies = [
  "log 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "num-traits 0.1.32 (registry+https://github.com/rust-lang/crates.io-index)",
  "num_cpus 0.2.12 (registry+https://github.com/rust-lang/crates.io-index)",
- "plugins 0.0.1",
  "rand 0.3.14 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc-serialize 0.3.19 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde 0.7.10 (registry+https://github.com/rust-lang/crates.io-index)",
diff --git a/components/style/Cargo.toml b/components/style/Cargo.toml
index 98492645bc7..4208b10a364 100644
--- a/components/style/Cargo.toml
+++ b/components/style/Cargo.toml
@@ -34,10 +34,10 @@ serde = {version = "0.7", features = ["nightly"]}
 serde_macros = "0.7"
 smallvec = "0.1"
 string_cache = {version = "0.2.20", features = ["heap_size"]}
-style_traits = {path = "../style_traits"}
+style_traits = {path = "../style_traits", features = ["heap_size"]}
 time = "0.1"
 url = {version = "1.0.0", features = ["heap_size"]}
-util = {path = "../util"}
+util = {path = "../util", features = ["servo"]}
 
 [build-dependencies]
 walkdir = "0.1"
diff --git a/components/style/logical_geometry.rs b/components/style/logical_geometry.rs
index b6afaf6f540..849fcc97f8d 100644
--- a/components/style/logical_geometry.rs
+++ b/components/style/logical_geometry.rs
@@ -5,7 +5,8 @@
 //! Geometry in flow-relative space.
 
 use euclid::num::Zero;
-use euclid::{Point2D, Rect, SideOffsets2D, Size2D};
+use euclid::side_offsets::SideOffsets2D;
+use euclid::{Point2D, Rect, Size2D};
 use std::cmp::{max, min};
 use std::fmt::{self, Debug, Error, Formatter};
 use std::ops::{Add, Sub};
diff --git a/components/style/properties/properties.mako.rs b/components/style/properties/properties.mako.rs
index 3d41c30366b..a65c9fb713c 100644
--- a/components/style/properties/properties.mako.rs
+++ b/components/style/properties/properties.mako.rs
@@ -25,7 +25,7 @@ use cssparser::{Parser, RGBA, AtRuleParser, DeclarationParser, Delimiter,
                 DeclarationListParser, parse_important, ToCss, TokenSerializationType};
 use error_reporting::ParseErrorReporter;
 use url::Url;
-use euclid::SideOffsets2D;
+use euclid::side_offsets::SideOffsets2D;
 use euclid::size::Size2D;
 use string_cache::Atom;
 use computed_values;
diff --git a/components/style_traits/Cargo.toml b/components/style_traits/Cargo.toml
index b089931d3cb..b8dd5079e95 100644
--- a/components/style_traits/Cargo.toml
+++ b/components/style_traits/Cargo.toml
@@ -8,13 +8,16 @@ publish = false
 name = "style_traits"
 path = "lib.rs"
 
+[features]
+heap_size = ["heapsize", "heapsize_plugin", "cssparser/heap_size", "euclid/plugins"]
+serde-serialization = ["serde", "serde_macros", "cssparser/serde-serialization", "euclid/plugins"]
+
 [dependencies]
 util = {path = "../util"}
-plugins = {path = "../plugins"}
-cssparser = {version = "0.5.4", features = ["heap_size", "serde-serialization"]}
-euclid = {version = "0.6.4", features = ["plugins"]}
-heapsize = "0.3.0"
-heapsize_plugin = "0.1.2"
+cssparser = "0.5.4"
+euclid = "0.6.4"
+heapsize = {version = "0.3.0", optional = true}
+heapsize_plugin = {version = "0.1.2", optional = true}
 rustc-serialize = "0.3"
-serde = "0.7"
-serde_macros = "0.7"
+serde = {version = "0.7", optional = true}
+serde_macros = {version = "0.7", optional = true}
diff --git a/components/style_traits/cursor.rs b/components/style_traits/cursor.rs
index be1d9b3c0b3..722a69a499a 100644
--- a/components/style_traits/cursor.rs
+++ b/components/style_traits/cursor.rs
@@ -8,7 +8,9 @@ use cssparser::ToCss;
 
 macro_rules! define_cursor {
     ($( $css: expr => $variant: ident = $value: expr, )+) => {
-        #[derive(Clone, Copy, Debug, Deserialize, Eq, HeapSizeOf, PartialEq, Serialize)]
+        #[derive(Clone, Copy, Debug, Eq, PartialEq)]
+        #[cfg_attr(feature = "serde-serialization", derive(Deserialize, Serialize))]
+        #[cfg_attr(feature = "heap_size", derive(HeapSizeOf))]
         #[repr(u8)]
         pub enum Cursor {
             $( $variant = $value ),+
diff --git a/components/style_traits/lib.rs b/components/style_traits/lib.rs
index 5cb01bb8c03..8cb3cb3769d 100644
--- a/components/style_traits/lib.rs
+++ b/components/style_traits/lib.rs
@@ -8,19 +8,22 @@
 
 #![crate_name = "style_traits"]
 #![crate_type = "rlib"]
-#![feature(custom_derive)]
-#![feature(plugin)]
-#![plugin(heapsize_plugin)]
-#![plugin(serde_macros)]
-#![plugin(plugins)]
+
 #![deny(unsafe_code)]
 
+#![cfg_attr(feature = "serde-serialization", feature(custom_derive))]
+#![cfg_attr(feature = "serde-serialization", feature(plugin))]
+#![cfg_attr(feature = "serde-serialization", plugin(serde_macros))]
+#![cfg_attr(feature = "heap_size", feature(custom_derive))]
+#![cfg_attr(feature = "heap_size", feature(plugin))]
+#![cfg_attr(feature = "heap_size", plugin(heapsize_plugin))]
+
 #[macro_use]
 extern crate cssparser;
 extern crate euclid;
-extern crate heapsize;
+#[cfg(feature = "heap_size")] extern crate heapsize;
 extern crate rustc_serialize;
-extern crate serde;
+#[cfg(feature = "serde-serialization")] extern crate serde;
 extern crate util;
 
 pub mod cursor;
diff --git a/components/style_traits/values.rs b/components/style_traits/values.rs
index 5b9226f324e..6139e2f5b53 100644
--- a/components/style_traits/values.rs
+++ b/components/style_traits/values.rs
@@ -5,12 +5,58 @@
 #[macro_export]
 macro_rules! define_css_keyword_enum {
     ($name: ident: $( $css: expr => $variant: ident ),+,) => {
-        define_css_keyword_enum!($name: $( $css => $variant ),+);
+        __define_css_keyword_enum__add_serde!($name [ $( $css => $variant ),+ ]);
     };
     ($name: ident: $( $css: expr => $variant: ident ),+) => {
+        __define_css_keyword_enum__add_serde!($name [ $( $css => $variant ),+ ]);
+    };
+}
+
+#[cfg(feature = "serde-serialization")]
+#[macro_export]
+macro_rules! __define_css_keyword_enum__add_serde {
+    ($name: ident [ $( $css: expr => $variant: ident ),+ ]) => {
+        __define_css_keyword_enum__add_heapsize! {
+            $name [ Deserialize, Serialize ] [ $( $css => $variant ),+ ]
+        }
+    };
+}
+
+#[cfg(not(feature = "serde-serialization"))]
+#[macro_export]
+macro_rules! __define_css_keyword_enum__add_serde {
+    ($name: ident [ $( $css: expr => $variant: ident ),+ ]) => {
+        __define_css_keyword_enum__add_heapsize! {
+            $name [] [ $( $css => $variant ),+ ]
+        }
+    };
+}
+
+#[cfg(feature = "heap_size")]
+#[macro_export]
+macro_rules! __define_css_keyword_enum__add_heapsize {
+    ($name: ident [ $( $derived_trait: ident),* ]  [ $( $css: expr => $variant: ident ),+ ]) => {
+        __define_css_keyword_enum__actual! {
+            $name [  $( $derived_trait, )* HeapSizeOf ] [ $( $css => $variant ),+ ]
+        }
+    };
+}
+
+#[cfg(not(feature = "heap_size"))]
+#[macro_export]
+macro_rules! __define_css_keyword_enum__add_heapsize {
+    ($name: ident [ $( $derived_trait: ident),* ]  [ $( $css: expr => $variant: ident ),+ ]) => {
+        __define_css_keyword_enum__actual! {
+            $name [ $( $derived_trait ),* ] [ $( $css => $variant ),+ ]
+        }
+    };
+}
+
+#[macro_export]
+macro_rules! __define_css_keyword_enum__actual {
+    ($name: ident [ $( $derived_trait: ident),* ] [ $( $css: expr => $variant: ident ),+ ]) => {
         #[allow(non_camel_case_types)]
-        #[derive(Clone, Eq, PartialEq, Copy, Hash, RustcEncodable, Debug, HeapSizeOf)]
-        #[derive(Deserialize, Serialize)]
+        #[derive(Clone, Eq, PartialEq, Copy, Hash, RustcEncodable, Debug $(, $derived_trait )* )]
         pub enum $name {
             $( $variant ),+
         }
diff --git a/components/style_traits/viewport.rs b/components/style_traits/viewport.rs
index f8b89ae4de6..ad71b8257cf 100644
--- a/components/style_traits/viewport.rs
+++ b/components/style_traits/viewport.rs
@@ -20,7 +20,9 @@ define_css_keyword_enum!(Orientation:
                          "landscape" => Landscape);
 
 
-#[derive(Clone, Debug, PartialEq, Deserialize, Serialize, HeapSizeOf)]
+#[derive(Clone, Debug, PartialEq)]
+#[cfg_attr(feature = "serde-serialization", derive(Deserialize, Serialize))]
+#[cfg_attr(feature = "heap_size", derive(HeapSizeOf))]
 pub struct ViewportConstraints {
     pub size: TypedSize2D<ViewportPx, f32>,
 
@@ -54,7 +56,8 @@ impl ToCss for ViewportConstraints {
 
 /// Zoom is a number | percentage | auto
 /// See http://dev.w3.org/csswg/css-device-adapt/#descdef-viewport-zoom
-#[derive(Copy, Clone, Debug, HeapSizeOf, PartialEq)]
+#[derive(Copy, Clone, Debug, PartialEq)]
+#[cfg_attr(feature = "heap_size", derive(HeapSizeOf))]
 pub enum Zoom {
     Number(f32),
     Percentage(f32),
diff --git a/components/util/Cargo.toml b/components/util/Cargo.toml
index 40c8f56a64b..334e474f56b 100644
--- a/components/util/Cargo.toml
+++ b/components/util/Cargo.toml
@@ -8,28 +8,30 @@ publish = false
 name = "util"
 path = "lib.rs"
 
+[features]
+# servo as opposed to geckolib
+servo = ["serde", "serde_macros", "backtrace", "ipc-channel", "bitflags"]
+
 [dependencies]
-app_units = {version = "0.2.3", features = ["plugins"]}
-backtrace = "0.2.1"
-bitflags = "0.7"
+app_units = {version = "0.2.3"}
+backtrace = {version = "0.2.1", optional = true}
+bitflags = {version = "0.7", optional = true}
 deque = "0.3.1"
-euclid = {version = "0.6.4", features = ["unstable", "plugins"]}
+euclid = {version = "0.6.4"}
 getopts = "0.2.11"
 heapsize = "0.3.0"
-heapsize_plugin = "0.1.2"
-ipc-channel = {git = "https://github.com/servo/ipc-channel"}
+ipc-channel = {git = "https://github.com/servo/ipc-channel", optional = true}
 lazy_static = "0.2"
 libc = "0.2"
 log = "0.3.5"
 num_cpus = "0.2.2"
 num-traits = "0.1.32"
-plugins = {path = "../plugins"}
 rand = "0.3"
 rustc-serialize = "0.3"
-serde = "0.7"
-serde_macros = "0.7"
+serde = {version = "0.7", optional = true}
+serde_macros = {version = "0.7", optional = true}
 smallvec = "0.1"
-url = {version = "1.0.0", features = ["heap_size", "serde"]}
+url = {version = "1.0.0"}
 
 [target.'cfg(all(unix, not(target_os = "macos"), not(target_os = "ios"), not(target_os = "android")))'.dependencies]
 xdg = "2.0"
diff --git a/components/util/geometry.rs b/components/util/geometry.rs
index 813cad3aa3d..d750131f151 100644
--- a/components/util/geometry.rs
+++ b/components/util/geometry.rs
@@ -23,7 +23,7 @@ use std::i32;
 ///
 /// The ratio between ScreenPx and DevicePixel for a given display be found by calling
 /// `servo::windowing::WindowMethods::hidpi_factor`.
-#[derive(Clone, Copy, Debug, HeapSizeOf)]
+#[derive(Clone, Copy, Debug)]
 pub enum ScreenPx {}
 
 /// One CSS "px" in the coordinate system of the "initial viewport":
@@ -35,7 +35,7 @@ pub enum ScreenPx {}
 ///
 /// At the default zoom level of 100%, one PagePx is equal to one ScreenPx.  However, if the
 /// document is zoomed in or out then this scale may be larger or smaller.
-#[derive(Clone, Copy, Debug, HeapSizeOf)]
+#[derive(Clone, Copy, Debug)]
 pub enum ViewportPx {}
 
 /// One CSS "px" in the root coordinate system for the content document.
@@ -44,9 +44,11 @@ pub enum ViewportPx {}
 /// This is the mobile-style "pinch zoom" that enlarges content without reflowing it.  When the
 /// viewport zoom is not equal to 1.0, then the layout viewport is no longer the same physical size
 /// as the viewable area.
-#[derive(Clone, Copy, Debug, HeapSizeOf)]
+#[derive(Clone, Copy, Debug)]
 pub enum PagePx {}
 
+known_heap_size!(0, ScreenPx, ViewportPx, PagePx);
+
 // In summary, the hierarchy of pixel units and the factors to convert from one to the next:
 //
 // DevicePixel
diff --git a/components/util/lib.rs b/components/util/lib.rs
index 6417fe40a45..8fe46dd6f7a 100644
--- a/components/util/lib.rs
+++ b/components/util/lib.rs
@@ -2,39 +2,31 @@
  * 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/. */
 
-#![feature(box_syntax)]
-#![feature(core_intrinsics)]
-#![feature(custom_derive)]
-#![feature(fnbox)]
-#![feature(plugin)]
-#![feature(reflect_marker)]
-#![feature(step_by)]
-
-#![plugin(heapsize_plugin, plugins, serde_macros)]
+#![cfg_attr(feature = "servo", feature(core_intrinsics))]
+#![cfg_attr(feature = "servo", feature(custom_derive))]
+#![cfg_attr(feature = "servo", feature(fnbox))]
+#![cfg_attr(feature = "servo", feature(plugin))]
+#![cfg_attr(feature = "servo", feature(reflect_marker))]
+#![cfg_attr(feature = "servo", plugin(serde_macros))]
 
 #![deny(unsafe_code)]
 
 extern crate app_units;
-extern crate backtrace;
-#[allow(unused_extern_crates)]
-#[macro_use]
-extern crate bitflags;
+#[cfg(feature = "servo")] extern crate backtrace;
+#[cfg(feature = "servo")] #[allow(unused_extern_crates)] #[macro_use] extern crate bitflags;
 extern crate deque;
 extern crate euclid;
 extern crate getopts;
-extern crate heapsize;
-extern crate ipc_channel;
-#[allow(unused_extern_crates)]
-#[macro_use]
-extern crate lazy_static;
+#[macro_use] extern crate heapsize;
+#[cfg(feature = "servo")] extern crate ipc_channel;
+#[allow(unused_extern_crates)] #[macro_use] extern crate lazy_static;
 extern crate libc;
-#[macro_use]
-extern crate log;
+#[macro_use] extern crate log;
 extern crate num_cpus;
 extern crate num_traits;
 extern crate rand;
 extern crate rustc_serialize;
-extern crate serde;
+#[cfg(feature = "servo")] extern crate serde;
 extern crate smallvec;
 extern crate url;
 #[cfg(all(unix, not(target_os = "macos"), not(target_os = "ios"), not(target_os = "android")))]
@@ -44,28 +36,24 @@ use std::sync::Arc;
 
 pub mod basedir;
 pub mod cache;
-#[allow(unsafe_code)]
-pub mod debug_utils;
+#[allow(unsafe_code)] pub mod debug_utils;
 pub mod geometry;
-#[allow(unsafe_code)]
-pub mod ipc;
-pub mod linked_list;
-#[allow(unsafe_code)]
-pub mod opts;
-pub mod panicking;
+#[cfg(feature = "servo")] #[allow(unsafe_code)] pub mod ipc;
+#[cfg(feature = "servo")] pub mod linked_list;
+#[allow(unsafe_code)] pub mod opts;
+#[cfg(feature = "servo")] pub mod panicking;
 pub mod prefs;
-pub mod print_tree;
+#[cfg(feature = "servo")] pub mod print_tree;
 pub mod resource_files;
-#[allow(unsafe_code)]
 pub mod str;
-pub mod thread;
-pub mod thread_state;
+#[cfg(feature = "servo")] pub mod thread;
+#[cfg(feature = "servo")] pub mod thread_state;
 pub mod tid;
-pub mod time;
+#[cfg(feature = "servo")] pub mod time;
 pub mod vec;
-#[allow(unsafe_code)]
-pub mod workqueue;
+#[cfg(feature = "servo")] #[allow(unsafe_code)] pub mod workqueue;
 
+#[cfg(feature = "servo")]
 #[allow(unsafe_code)]
 pub fn breakpoint() {
     unsafe { ::std::intrinsics::breakpoint() };
diff --git a/components/util/opts.rs b/components/util/opts.rs
index 323abc19d62..711782ab3ea 100644
--- a/components/util/opts.rs
+++ b/components/util/opts.rs
@@ -23,7 +23,8 @@ use url::{self, Url};
 
 
 /// Global flags for Servo, currently set on the command line.
-#[derive(Clone, Deserialize, Serialize)]
+#[derive(Clone)]
+#[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
 pub struct Opts {
     pub is_running_problem_test: bool,
 
@@ -379,7 +380,8 @@ pub fn print_debug_usage(app: &str) -> ! {
     process::exit(0)
 }
 
-#[derive(Clone, Deserialize, Serialize)]
+#[derive(Clone)]
+#[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
 pub enum OutputOptions {
     FileName(String),
     Stdout(f64)
@@ -404,7 +406,8 @@ enum UserAgent {
     Android,
 }
 
-#[derive(Clone, Debug, Eq, Deserialize, PartialEq, Serialize)]
+#[derive(Clone, Debug, Eq, PartialEq)]
+#[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
 pub enum RenderApi {
     GL,
     ES2,
@@ -858,7 +861,7 @@ pub fn set_defaults(opts: Opts) {
     unsafe {
         assert!(DEFAULT_OPTIONS.is_null());
         assert!(DEFAULT_OPTIONS != INVALID_OPTIONS);
-        let box_opts = box opts;
+        let box_opts = Box::new(opts);
         DEFAULT_OPTIONS = Box::into_raw(box_opts);
     }
 }
diff --git a/components/util/prefs.rs b/components/util/prefs.rs
index 9c713df02e9..55c856fa747 100644
--- a/components/util/prefs.rs
+++ b/components/util/prefs.rs
@@ -20,7 +20,8 @@ lazy_static! {
     };
 }
 
-#[derive(PartialEq, Clone, Debug, Deserialize, Serialize)]
+#[derive(PartialEq, Clone, Debug)]
+#[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
 pub enum PrefValue {
     Boolean(bool),
     String(String),
@@ -91,7 +92,8 @@ impl ToJson for PrefValue {
     }
 }
 
-#[derive(Clone, Debug, Deserialize, Serialize)]
+#[derive(Clone, Debug)]
+#[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
 pub enum Pref {
     NoDefault(Arc<PrefValue>),
     WithDefault(Arc<PrefValue>, Option<Arc<PrefValue>>)
diff --git a/components/util/vec.rs b/components/util/vec.rs
index 5342d452020..639e1c260da 100644
--- a/components/util/vec.rs
+++ b/components/util/vec.rs
@@ -9,10 +9,13 @@ use super::smallvec::VecLike;
 // TODO(pcwalton): Speed up with SIMD, or better yet, find some way to not do this.
 pub fn byte_swap(data: &mut [u8]) {
     let length = data.len();
-    for i in (0..length).step_by(4) {
+    // FIXME(rust #27741): Range::step_by is not stable yet as of this writing.
+    let mut i = 0;
+    while i < length {
         let r = data[i + 2];
         data[i + 2] = data[i + 0];
         data[i + 0] = r;
+        i += 4;
     }
 }