Auto merge of #13759 - bholley:owning_handle, r=SimonSapin

Implement OwningHandle in style

I've also PR-ed this against upstream [1], but I don't want to block on that in case it takes a while to be merged / published.

[1] https://github.com/Kimundi/owning-ref-rs/pull/15

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components/servo/Cargo.lock

@@ -1727,7 +1727,7 @@ dependencies = [
 
 [[package]]
 name = "owning_ref"
-version = "0.2.1"
+version = "0.2.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
@@ -1735,7 +1735,7 @@ name = "parking_lot"
 version = "0.3.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "owning_ref 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "owning_ref 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "parking_lot_core 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -2320,6 +2320,7 @@ dependencies = [
  "num-traits 0.1.35 (registry+https://github.com/rust-lang/crates.io-index)",
  "num_cpus 0.2.13 (registry+https://github.com/rust-lang/crates.io-index)",
  "ordered-float 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "owning_ref 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "parking_lot 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "plugins 0.0.1",
  "quickersort 2.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2344,6 +2345,7 @@ dependencies = [
  "app_units 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "cssparser 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "euclid 0.10.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "owning_ref 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "parking_lot 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc-serialize 0.3.19 (registry+https://github.com/rust-lang/crates.io-index)",
  "selectors 0.13.1 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2960,7 +2962,7 @@ dependencies = [
 "checksum osmesa-src 12.0.1 (git+https://github.com/servo/osmesa-src)" = "<none>"
 "checksum osmesa-sys 0.1.2 (git+https://github.com/daggerbot/osmesa-rs)" = "<none>"
 "checksum osmesa-sys 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)" = "88cfece6e95d2e717e0872a7f53a8684712ad13822a7979bc760b9c77ec0013b"
-"checksum owning_ref 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "88084505837507cbec6a9f39b5d3b985db3c84e9a741c80200b619001283293d"
+"checksum owning_ref 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)" = "8d91377085359426407a287ab16884a0111ba473aa6844ff01d4ec20ce3d75e7"
 "checksum parking_lot 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "3562f3de7bdff194212be82366abf5c6565aff8a433b71c53c63d0e7c9913878"
 "checksum parking_lot_core 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)" = "06f24c980718110494e9cfb7db7438895c3f54505101bb6170329d5e43a53f64"
 "checksum phf 0.7.17 (registry+https://github.com/rust-lang/crates.io-index)" = "f02853ab706e88121d7ad33ed06bedce0a7cdb96136be7c20ff0dce7b4adb9ef"

components/style/Cargo.toml

@@ -41,6 +41,7 @@ num-integer = "0.1.32"
 num-traits = "0.1.32"
 num_cpus = "0.2.2"
 ordered-float = "0.2.2"
+owning_ref = "0.2.2"
 parking_lot = "0.3.3"
 quickersort = "2.0.0"
 rand = "0.3"

components/style/lib.rs

@@ -73,6 +73,7 @@ extern crate num_integer;
 extern crate num_traits;
 #[cfg(feature = "gecko")] extern crate num_cpus;
 extern crate ordered_float;
+extern crate owning_ref;
 extern crate parking_lot;
 extern crate quickersort;
 extern crate rand;
@@ -112,6 +113,7 @@ pub mod keyframes;
 pub mod logical_geometry;
 pub mod matching;
 pub mod media_queries;
+pub mod owning_handle;
 pub mod parallel;
 pub mod parser;
 pub mod refcell;

components/style/owning_handle.rs

@@ -0,0 +1,81 @@
+/* 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/. */
+
+#![allow(unsafe_code)]
+
+use owning_ref::StableAddress;
+use std::ops::{Deref, DerefMut};
+
+/// `OwningHandle` is a complement to `OwningRef`. Where `OwningRef` allows
+/// consumers to pass around an owned object and a dependent reference,
+/// `OwningHandle` contains an owned object and a dependent _object_.
+///
+/// `OwningHandle` can encapsulate a `RefMut` along with its associated
+/// `RefCell`, or an `RwLockReadGuard` along with its associated `RwLock`.
+/// However, the API is completely generic and there are no restrictions on
+/// what types of owning and dependent objects may be used.
+///
+/// `OwningHandle` is created by passing an owner object (which dereferences
+/// to a stable address) along with a callback which receives a pointer to
+/// that stable location. The callback may then dereference the pointer and
+/// mint a dependent object, with the guarantee that the returned object will
+/// not outlive the referent of the pointer.
+///
+/// This does foist some unsafety onto the callback, which needs an `unsafe`
+/// block to dereference the pointer. It would be almost good enough for
+/// OwningHandle to pass a transmuted &'statc reference to the callback
+/// since the lifetime is infinite as far as the minted handle is concerned.
+/// However, even an `Fn` callback can still allow the reference to escape
+/// via a `StaticMutex` or similar, which technically violates the safety
+/// contract. Some sort of language support in the lifetime system could
+/// make this API a bit nicer.
+pub struct OwningHandle<O, H>
+    where O: StableAddress, H: Deref,
+{
+    handle: H,
+    _owner: O,
+}
+
+impl<O, H> Deref for OwningHandle<O, H>
+    where O: StableAddress, H: Deref,
+{
+    type Target = H::Target;
+    fn deref(&self) -> &H::Target {
+        self.handle.deref()
+    }
+}
+
+unsafe impl<O, H> StableAddress for OwningHandle<O, H>
+    where O: StableAddress, H: StableAddress,
+{}
+
+impl<O, H> DerefMut for OwningHandle<O, H>
+    where O: StableAddress, H: DerefMut,
+{
+    fn deref_mut(&mut self) -> &mut H::Target {
+        self.handle.deref_mut()
+    }
+}
+
+impl<O, H> OwningHandle<O, H>
+    where O: StableAddress, H: Deref,
+{
+    /// Create a new OwningHandle. The provided callback will be invoked with
+    /// a pointer to the object owned by `o`, and the returned value is stored
+    /// as the object to which this `OwningHandle` will forward `Deref` and
+    /// `DerefMut`.
+    pub fn new<F>(o: O, f: F) -> Self
+        where F: Fn(*const O::Target) -> H
+    {
+        let h: H;
+        {
+            h = f(o.deref() as *const O::Target);
+        }
+
+        OwningHandle {
+          handle: h,
+          _owner: o,
+        }
+    }
+}

ports/cef/Cargo.lock

@@ -1598,7 +1598,7 @@ dependencies = [
 
 [[package]]
 name = "owning_ref"
-version = "0.2.1"
+version = "0.2.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
@@ -1606,7 +1606,7 @@ name = "parking_lot"
 version = "0.3.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "owning_ref 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "owning_ref 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "parking_lot_core 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -2203,6 +2203,7 @@ dependencies = [
  "num-traits 0.1.35 (registry+https://github.com/rust-lang/crates.io-index)",
  "num_cpus 0.2.13 (registry+https://github.com/rust-lang/crates.io-index)",
  "ordered-float 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "owning_ref 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "parking_lot 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "plugins 0.0.1",
  "quickersort 2.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2813,7 +2814,7 @@ dependencies = [
 "checksum osmesa-src 12.0.1 (git+https://github.com/servo/osmesa-src)" = "<none>"
 "checksum osmesa-sys 0.1.2 (git+https://github.com/daggerbot/osmesa-rs)" = "<none>"
 "checksum osmesa-sys 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)" = "88cfece6e95d2e717e0872a7f53a8684712ad13822a7979bc760b9c77ec0013b"
-"checksum owning_ref 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "88084505837507cbec6a9f39b5d3b985db3c84e9a741c80200b619001283293d"
+"checksum owning_ref 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)" = "8d91377085359426407a287ab16884a0111ba473aa6844ff01d4ec20ce3d75e7"
 "checksum parking_lot 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "3562f3de7bdff194212be82366abf5c6565aff8a433b71c53c63d0e7c9913878"
 "checksum parking_lot_core 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)" = "06f24c980718110494e9cfb7db7438895c3f54505101bb6170329d5e43a53f64"
 "checksum phf 0.7.17 (registry+https://github.com/rust-lang/crates.io-index)" = "f02853ab706e88121d7ad33ed06bedce0a7cdb96136be7c20ff0dce7b4adb9ef"

ports/geckolib/Cargo.lock

@@ -251,7 +251,7 @@ dependencies = [
 
 [[package]]
 name = "owning_ref"
-version = "0.2.1"
+version = "0.2.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
@@ -259,7 +259,7 @@ name = "parking_lot"
 version = "0.3.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "owning_ref 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "owning_ref 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "parking_lot_core 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -385,6 +385,7 @@ dependencies = [
  "num-traits 0.1.35 (registry+https://github.com/rust-lang/crates.io-index)",
  "num_cpus 0.2.13 (registry+https://github.com/rust-lang/crates.io-index)",
  "ordered-float 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "owning_ref 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "parking_lot 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "quickersort 2.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "rand 0.3.14 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -567,7 +568,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum num-traits 0.1.35 (registry+https://github.com/rust-lang/crates.io-index)" = "8359ea48994f253fa958b5b90b013728b06f54872e5a58bce39540fcdd0f2527"
 "checksum num_cpus 0.2.13 (registry+https://github.com/rust-lang/crates.io-index)" = "cee7e88156f3f9e19bdd598f8d6c9db7bf4078f99f8381f43a55b09648d1a6e3"
 "checksum ordered-float 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "cc511538298611a79d5a4ddfbb75315b866d942ed26a00bdc3590795c68b7279"
-"checksum owning_ref 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "88084505837507cbec6a9f39b5d3b985db3c84e9a741c80200b619001283293d"
+"checksum owning_ref 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)" = "8d91377085359426407a287ab16884a0111ba473aa6844ff01d4ec20ce3d75e7"
 "checksum parking_lot 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "3562f3de7bdff194212be82366abf5c6565aff8a433b71c53c63d0e7c9913878"
 "checksum parking_lot_core 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)" = "06f24c980718110494e9cfb7db7438895c3f54505101bb6170329d5e43a53f64"
 "checksum phf_generator 0.7.16 (registry+https://github.com/rust-lang/crates.io-index)" = "04b5ea825e28cb6efd89d9133b129b2003b45a221aeda025509b125b00ecb7c4"

tests/unit/style/Cargo.toml

@@ -13,6 +13,7 @@ doctest = false
 app_units = "0.3"
 cssparser = {version = "0.7", features = ["heap_size"]}
 euclid = "0.10.1"
+owning_ref = "0.2.2"
 parking_lot = "0.3"
 rustc-serialize = "0.3"
 selectors = "0.13"

tests/unit/style/lib.rs

@@ -9,6 +9,7 @@
 extern crate app_units;
 extern crate cssparser;
 extern crate euclid;
+extern crate owning_ref;
 extern crate parking_lot;
 extern crate rustc_serialize;
 extern crate selectors;
@@ -22,6 +23,7 @@ mod attr;
 mod cache;
 mod logical_geometry;
 mod media_queries;
+mod owning_handle;
 mod parsing;
 mod properties;
 mod selector_matching;

tests/unit/style/owning_handle.rs

@@ -0,0 +1,34 @@
+/* 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/. */
+
+use owning_ref::RcRef;
+use std::cell::RefCell;
+use std::rc::Rc;
+use std::sync::{Arc, RwLock};
+use style::owning_handle::OwningHandle;
+
+#[test]
+fn owning_handle() {
+    use std::cell::RefCell;
+    let cell = Rc::new(RefCell::new(2));
+    let cell_ref = RcRef::new(cell);
+    let mut handle = OwningHandle::new(cell_ref, |x| unsafe { x.as_ref() }.unwrap().borrow_mut());
+    assert_eq!(*handle, 2);
+    *handle = 3;
+    assert_eq!(*handle, 3);
+}
+
+#[test]
+fn nested() {
+    let result = {
+        let complex = Rc::new(RefCell::new(Arc::new(RwLock::new("someString"))));
+        let curr = RcRef::new(complex);
+        let curr = OwningHandle::new(curr, |x| unsafe { x.as_ref() }.unwrap().borrow_mut());
+        let mut curr = OwningHandle::new(curr, |x| unsafe { x.as_ref() }.unwrap().try_write().unwrap());
+        assert_eq!(*curr, "someString");
+        *curr = "someOtherString";
+        curr
+    };
+    assert_eq!(*result, "someOtherString");
+}