Revert changes to servo_arc, style_derive, and style_traits (#31387)

This reverts the Rust edition updates to these three traits as well as
incorporates https://phabricator.services.mozilla.com/D117887. The
purpose of this change is to reduce the diff with upstream stylo.

Finally, formatting is disabled for these crates as well.

2 files changed, 18 insertions, 22 deletions

diff --git a/components/servo_arc/Cargo.toml b/components/servo_arc/Cargo.toml
index 0f50d9cd41f..c975ad55412 100644
--- a/components/servo_arc/Cargo.toml
+++ b/components/servo_arc/Cargo.toml
@@ -5,7 +5,6 @@ authors = ["The Servo Project Developers"]
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/servo/servo"
 description = "A fork of std::sync::Arc with some extra functionality and without weak references"
-edition = "2018"
 
 [lib]
 name = "servo_arc"
diff --git a/components/servo_arc/lib.rs b/components/servo_arc/lib.rs
index a201e5f7065..cc71827283a 100644
--- a/components/servo_arc/lib.rs
+++ b/components/servo_arc/lib.rs
@@ -25,23 +25,30 @@
 // duplicate those here.
 #![allow(missing_docs)]
 
+#[cfg(feature = "servo")]
+extern crate serde;
+extern crate stable_deref_trait;
+
+#[cfg(feature = "servo")]
+use serde::{Deserialize, Serialize};
+use stable_deref_trait::{CloneStableDeref, StableDeref};
 use std::alloc::{self, Layout};
+use std::borrow;
 use std::cmp::Ordering;
 use std::convert::From;
+use std::fmt;
 use std::hash::{Hash, Hasher};
 use std::iter::{ExactSizeIterator, Iterator};
 use std::marker::PhantomData;
 use std::mem::{self, align_of, size_of};
 use std::ops::{Deref, DerefMut};
 use std::os::raw::c_void;
+use std::process;
+use std::ptr;
+use std::slice;
 use std::sync::atomic;
 use std::sync::atomic::Ordering::{Acquire, Relaxed, Release};
-use std::{borrow, fmt, isize, process, ptr, slice, usize};
-
-use nodrop::NoDrop;
-#[cfg(feature = "servo")]
-use serde::{Deserialize, Serialize};
-use stable_deref_trait::{CloneStableDeref, StableDeref};
+use std::{isize, usize};
 
 /// A soft limit on the amount of references that may be made to an `Arc`.
 ///
@@ -811,6 +818,7 @@ impl<H, T> Arc<HeaderSlice<H, [T]>> {
 
     /// Creates an Arc for a HeaderSlice using the given header struct and
     /// iterator to generate the slice. The resulting Arc will be fat.
+    #[inline]
     pub fn from_header_and_iter<I>(header: H, items: I) -> Self
     where
         I: Iterator<Item = T> + ExactSizeIterator,
@@ -904,7 +912,7 @@ impl<H, T> ThinArc<H, T> {
     {
         // Synthesize transient Arc, which never touches the refcount of the ArcInner.
         let transient = unsafe {
-            NoDrop::new(Arc {
+            mem::ManuallyDrop::new(Arc {
                 p: ptr::NonNull::new_unchecked(thin_to_thick(self.ptr.as_ptr())),
                 phantom: PhantomData,
             })
@@ -913,11 +921,6 @@ impl<H, T> ThinArc<H, T> {
         // Expose the transient Arc to the callback, which may clone it if it wants.
         let result = f(&transient);
 
-        // Forget the transient Arc to leave the refcount untouched.
-        // XXXManishearth this can be removed when unions stabilize,
-        // since then NoDrop becomes zero overhead
-        mem::forget(transient);
-
         // Forward the result.
         result
     }
@@ -1129,7 +1132,7 @@ impl<'a, T> ArcBorrow<'a, T> {
     /// Compare two `ArcBorrow`s via pointer equality. Will only return
     /// true if they come from the same allocation
     pub fn ptr_eq(this: &Self, other: &Self) -> bool {
-        std::ptr::eq(this.0, other.0)
+        this.0 as *const T == other.0 as *const T
     }
 
     /// Temporarily converts |self| into a bonafide Arc and exposes it to the
@@ -1141,16 +1144,11 @@ impl<'a, T> ArcBorrow<'a, T> {
         T: 'static,
     {
         // Synthesize transient Arc, which never touches the refcount.
-        let transient = unsafe { NoDrop::new(Arc::from_raw(self.0)) };
+        let transient = unsafe { mem::ManuallyDrop::new(Arc::from_raw(self.0)) };
 
         // Expose the transient Arc to the callback, which may clone it if it wants.
         let result = f(&transient);
 
-        // Forget the transient Arc to leave the refcount untouched.
-        // XXXManishearth this can be removed when unions stabilize,
-        // since then NoDrop becomes zero overhead
-        mem::forget(transient);
-
         // Forward the result.
         result
     }
@@ -1309,13 +1307,12 @@ impl<A: fmt::Debug, B: fmt::Debug> fmt::Debug for ArcUnion<A, B> {
 
 #[cfg(test)]
 mod tests {
+    use super::{Arc, HeaderWithLength, ThinArc};
     use std::clone::Clone;
     use std::ops::Drop;
     use std::sync::atomic;
     use std::sync::atomic::Ordering::{Acquire, SeqCst};
 
-    use super::{Arc, HeaderWithLength, ThinArc};
-
     #[derive(PartialEq)]
     struct Canary(*mut atomic::AtomicUsize);