Move DOMRefCell back into script.

We’re not using it in style after all.

components/script/dom/bindings/cell.rs

@@ -0,0 +1,135 @@
+/* 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 shareable mutable container for the DOM.
+
+use style::refcell::{BorrowError, BorrowMutError, Ref, RefCell, RefMut};
+use style::thread_state;
+
+/// A mutable field in the DOM.
+///
+/// This extends the API of `core::cell::RefCell` to allow unsafe access in
+/// certain situations, with dynamic checking in debug builds.
+#[derive(Clone, PartialEq, Debug, HeapSizeOf)]
+pub struct DOMRefCell<T> {
+    value: RefCell<T>,
+}
+
+// FIXME: These two impls make promises that are not quite true,
+// but maybe the debug_assert! makes it close enough.
+#[allow(unsafe_code)]
+unsafe impl<T: Send> Send for DOMRefCell<T> {}
+#[allow(unsafe_code)]
+unsafe impl<T: Sync> Sync for DOMRefCell<T> {}
+
+// Functionality specific to Servo's `DOMRefCell` type
+// ===================================================
+
+impl<T> DOMRefCell<T> {
+    /// Return a reference to the contents.
+    ///
+    /// For use in the layout thread only.
+    #[allow(unsafe_code)]
+    pub unsafe fn borrow_for_layout(&self) -> &T {
+        debug_assert!(thread_state::get().is_layout());
+        &*self.value.as_ptr()
+    }
+
+    /// Borrow the contents for the purpose of GC tracing.
+    ///
+    /// This succeeds even if the object is mutably borrowed,
+    /// so you have to be careful in trace code!
+    #[allow(unsafe_code)]
+    pub unsafe fn borrow_for_gc_trace(&self) -> &T {
+        // FIXME: IN_GC isn't reliable enough - doesn't catch minor GCs
+        // https://github.com/servo/servo/issues/6389
+        // debug_assert!(thread_state::get().contains(SCRIPT | IN_GC));
+        &*self.value.as_ptr()
+    }
+
+    /// Borrow the contents for the purpose of script deallocation.
+    ///
+    #[allow(unsafe_code)]
+    pub unsafe fn borrow_for_script_deallocation(&self) -> &mut T {
+        debug_assert!(thread_state::get().contains(thread_state::SCRIPT));
+        &mut *self.value.as_ptr()
+    }
+
+    /// Version of the above that we use during restyle while the script thread
+    /// is blocked.
+    pub fn borrow_mut_for_layout(&self) -> RefMut<T> {
+        debug_assert!(thread_state::get().is_layout());
+        self.value.borrow_mut()
+    }
+}
+
+// Functionality duplicated with `core::cell::RefCell`
+// ===================================================
+impl<T> DOMRefCell<T> {
+    /// Create a new `DOMRefCell` containing `value`.
+    pub fn new(value: T) -> DOMRefCell<T> {
+        DOMRefCell {
+            value: RefCell::new(value),
+        }
+    }
+
+
+    /// Immutably borrows the wrapped value.
+    ///
+    /// The borrow lasts until the returned `Ref` exits scope. Multiple
+    /// immutable borrows can be taken out at the same time.
+    ///
+    /// # Panics
+    ///
+    /// Panics if this is called off the script thread.
+    ///
+    /// Panics if the value is currently mutably borrowed.
+    pub fn borrow(&self) -> Ref<T> {
+        self.try_borrow().expect("DOMRefCell<T> already mutably borrowed")
+    }
+
+    /// Mutably borrows the wrapped value.
+    ///
+    /// The borrow lasts until the returned `RefMut` exits scope. The value
+    /// cannot be borrowed while this borrow is active.
+    ///
+    /// # Panics
+    ///
+    /// Panics if this is called off the script thread.
+    ///
+    /// Panics if the value is currently borrowed.
+    pub fn borrow_mut(&self) -> RefMut<T> {
+        self.try_borrow_mut().expect("DOMRefCell<T> already borrowed")
+    }
+
+    /// Attempts to immutably borrow the wrapped value.
+    ///
+    /// The borrow lasts until the returned `Ref` exits scope. Multiple
+    /// immutable borrows can be taken out at the same time.
+    ///
+    /// Returns `None` if the value is currently mutably borrowed.
+    ///
+    /// # Panics
+    ///
+    /// Panics if this is called off the script thread.
+    pub fn try_borrow(&self) -> Result<Ref<T>, BorrowError<T>> {
+        debug_assert!(thread_state::get().is_script());
+        self.value.try_borrow()
+    }
+
+    /// Mutably borrows the wrapped value.
+    ///
+    /// The borrow lasts until the returned `RefMut` exits scope. The value
+    /// cannot be borrowed while this borrow is active.
+    ///
+    /// Returns `None` if the value is currently borrowed.
+    ///
+    /// # Panics
+    ///
+    /// Panics if this is called off the script thread.
+    pub fn try_borrow_mut(&self) -> Result<RefMut<T>, BorrowMutError<T>> {
+        debug_assert!(thread_state::get().is_script());
+        self.value.try_borrow_mut()
+    }
+}

components/script/dom/bindings/mod.rs

@@ -128,9 +128,8 @@
 //! return `Err()` from the method with the appropriate [error value]
 //! (error/enum.Error.html).
 
-pub use style::domrefcell as cell;
-
 pub mod callback;
+pub mod cell;
 pub mod constant;
 pub mod conversions;
 pub mod error;

components/script/dom/bindings/trace.rs

@@ -35,6 +35,7 @@ use cssparser::RGBA;
 use devtools_traits::CSSError;
 use devtools_traits::WorkerId;
 use dom::abstractworker::SharedRt;
+use dom::bindings::cell::DOMRefCell;
 use dom::bindings::js::{JS, Root};
 use dom::bindings::refcounted::{Trusted, TrustedPromise};
 use dom::bindings::reflector::{Reflectable, Reflector};
@@ -89,7 +90,6 @@ use std::sync::mpsc::{Receiver, Sender};
 use std::time::{SystemTime, Instant};
 use string_cache::{Atom, Namespace, QualName};
 use style::attr::{AttrIdentifier, AttrValue, LengthOrPercentageOrAuto};
-use style::domrefcell::DOMRefCell;
 use style::element_state::*;
 use style::properties::PropertyDeclarationBlock;
 use style::selector_impl::{ElementSnapshot, PseudoElement};