Auto merge of #16976 - upsuper:bug1366247, r=nox

Add sugar for already_AddRefed

This is Servo side change of [bug 1366247](https://bugzilla.mozilla.org/show_bug.cgi?id=1366247).

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6 files changed, 75 insertions, 26 deletions

diff --git a/components/style/gecko/generated/bindings.rs b/components/style/gecko/generated/bindings.rs
index c88d389bd3b..2987408705d 100644
--- a/components/style/gecko/generated/bindings.rs
+++ b/components/style/gecko/generated/bindings.rs
@@ -1,13 +1,13 @@
 /* automatically generated by rust-bindgen */
 
 pub use nsstring::{nsACString, nsAString, nsString, nsStringRepr};
-use gecko_bindings::structs::nsTArray;
 type nsACString_internal = nsACString;
 type nsAString_internal = nsAString;
 use gecko_bindings::structs::mozilla::css::GridTemplateAreasValue;
 use gecko_bindings::structs::mozilla::css::ImageValue;
 use gecko_bindings::structs::mozilla::css::URLValue;
 use gecko_bindings::structs::mozilla::Side;
+use gecko_bindings::structs::already_AddRefed;
 use gecko_bindings::structs::RawGeckoAnimationPropertySegment;
 use gecko_bindings::structs::RawGeckoComputedTiming;
 use gecko_bindings::structs::RawGeckoCSSPropertyIDList;
@@ -190,6 +190,7 @@ unsafe impl Sync for nsStyleVisibility {}
 use gecko_bindings::structs::nsStyleXUL;
 unsafe impl Send for nsStyleXUL {}
 unsafe impl Sync for nsStyleXUL {}
+use gecko_bindings::structs::nsTArray;
 use gecko_bindings::structs::nsTimingFunction;
 use gecko_bindings::structs::nscolor;
 use gecko_bindings::structs::nscoord;
@@ -1237,7 +1238,7 @@ extern "C" {
 }
 extern "C" {
     pub fn Gecko_CSSValue_SetAtomIdent(css_value: nsCSSValueBorrowedMut,
-                                       atom: *mut nsIAtom);
+                                       atom: already_AddRefed<nsIAtom>);
 }
 extern "C" {
     pub fn Gecko_CSSValue_SetArray(css_value: nsCSSValueBorrowedMut,
@@ -1981,7 +1982,7 @@ extern "C" {
 }
 extern "C" {
     pub fn Servo_KeyframesRule_SetName(rule: RawServoKeyframesRuleBorrowed,
-                                       name: *mut nsIAtom);
+                                       name: already_AddRefed<nsIAtom>);
 }
 extern "C" {
     pub fn Servo_KeyframesRule_GetCount(rule: RawServoKeyframesRuleBorrowed)
diff --git a/components/style/gecko/wrapper.rs b/components/style/gecko/wrapper.rs
index e043ff57223..71e26e104a4 100644
--- a/components/style/gecko/wrapper.rs
+++ b/components/style/gecko/wrapper.rs
@@ -54,6 +54,7 @@ use gecko_bindings::structs::ELEMENT_HAS_SNAPSHOT;
 use gecko_bindings::structs::EffectCompositor_CascadeLevel as CascadeLevel;
 use gecko_bindings::structs::NODE_IS_IN_NATIVE_ANONYMOUS_SUBTREE;
 use gecko_bindings::structs::NODE_IS_NATIVE_ANONYMOUS;
+use gecko_bindings::structs::already_AddRefed;
 use gecko_bindings::sugar::ownership::HasArcFFI;
 use logical_geometry::WritingMode;
 use media_queries::Device;
@@ -1074,13 +1075,13 @@ impl<'le> PresentationalHintsSynthesizer for GeckoElement<'le> {
         //
         // http://www.whatwg.org/specs/web-apps/current-work/multipage/elements.html#language
         let ptr = unsafe {
-            bindings::Gecko_GetXMLLangValue(self.0)
+            already_AddRefed::new(bindings::Gecko_GetXMLLangValue(self.0))
         };
-        if !ptr.is_null() {
+        if let Some(ptr) = ptr {
             let global_style_data = &*GLOBAL_STYLE_DATA;
 
             let pdb = PropertyDeclarationBlock::with_one(
-                PropertyDeclaration::XLang(SpecifiedLang(unsafe { Atom::from_addrefed(ptr) })),
+                PropertyDeclaration::XLang(SpecifiedLang(ptr.into())),
                 Importance::Normal
             );
             let arc = Arc::new(global_style_data.shared_lock.wrap(pdb));
diff --git a/components/style/gecko_bindings/sugar/already_addrefed.rs b/components/style/gecko_bindings/sugar/already_addrefed.rs
new file mode 100644
index 00000000000..01e209fc81f
--- /dev/null
+++ b/components/style/gecko_bindings/sugar/already_addrefed.rs
@@ -0,0 +1,48 @@
+/* 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/. */
+
+//! little helpers for `already_AddRefed`.
+
+use gecko_bindings::structs::already_AddRefed;
+use std::marker::PhantomData;
+use std::mem;
+
+impl<T> already_AddRefed<T> {
+    /// Create an already_AddRefed from an addrefed pointer.
+    #[inline]
+    pub unsafe fn new(ptr: *mut T) -> Option<Self> {
+        if !ptr.is_null() {
+            Some(Self::new_unchecked(ptr))
+        } else {
+            None
+        }
+    }
+
+    /// Create an already_AddRefed from an non-nullable addrefed pointer.
+    #[inline]
+    pub unsafe fn new_unchecked(ptr: *mut T) -> Self {
+        debug_assert!(!ptr.is_null());
+        already_AddRefed {
+            mRawPtr: ptr,
+            _phantom_0: PhantomData,
+        }
+    }
+
+    /// Take the addrefed pointer from this struct.
+    #[inline]
+    pub fn take(self) -> *mut T {
+        let ptr = self.mRawPtr;
+        mem::forget(self);
+        ptr
+    }
+}
+
+#[cfg(debug_assertions)]
+impl<T> Drop for already_AddRefed<T> {
+    fn drop(&mut self) {
+        // We really should instead mark already_AddRefed must_use, but
+        // we cannot currently, which is servo/rust-bindgen#710.
+        unreachable!("Destructor shouldn't be called, otherwise we are leaking")
+    }
+}
diff --git a/components/style/gecko_bindings/sugar/mod.rs b/components/style/gecko_bindings/sugar/mod.rs
index f241c94810b..112a8d8e4fa 100644
--- a/components/style/gecko_bindings/sugar/mod.rs
+++ b/components/style/gecko_bindings/sugar/mod.rs
@@ -4,6 +4,7 @@
 
 //! Rust sugar and convenience methods for Gecko types.
 
+mod already_addrefed;
 mod ns_com_ptr;
 mod ns_compatibility;
 mod ns_css_shadow_array;
diff --git a/components/style/gecko_bindings/sugar/ns_css_value.rs b/components/style/gecko_bindings/sugar/ns_css_value.rs
index 0f91fc4f27a..13c3c5a825c 100644
--- a/components/style/gecko_bindings/sugar/ns_css_value.rs
+++ b/components/style/gecko_bindings/sugar/ns_css_value.rs
@@ -152,7 +152,7 @@ impl nsCSSValue {
 
     /// Set to an atom identifier value
     pub fn set_atom_ident(&mut self, s: Atom) {
-        unsafe { bindings::Gecko_CSSValue_SetAtomIdent(self, s.into_addrefed()) }
+        unsafe { bindings::Gecko_CSSValue_SetAtomIdent(self, s.into()) }
     }
 
     /// Set to a font format
diff --git a/components/style/gecko_string_cache/mod.rs b/components/style/gecko_string_cache/mod.rs
index fa89f5eab48..08933c053ff 100644
--- a/components/style/gecko_string_cache/mod.rs
+++ b/components/style/gecko_string_cache/mod.rs
@@ -10,7 +10,7 @@ use gecko_bindings::bindings::Gecko_AddRefAtom;
 use gecko_bindings::bindings::Gecko_Atomize;
 use gecko_bindings::bindings::Gecko_Atomize16;
 use gecko_bindings::bindings::Gecko_ReleaseAtom;
-use gecko_bindings::structs::nsIAtom;
+use gecko_bindings::structs::{already_AddRefed, nsIAtom};
 use nsstring::nsAString;
 use precomputed_hash::PrecomputedHash;
 use std::ascii::AsciiExt;
@@ -219,24 +219,6 @@ impl Atom {
         atom
     }
 
-    /// Creates an atom from a dynamic atom pointer that has already had AddRef
-    /// called on it.
-    #[inline]
-    pub unsafe fn from_addrefed(ptr: *mut nsIAtom) -> Self {
-        debug_assert!(!ptr.is_null());
-        unsafe {
-            Atom(WeakAtom::new(ptr))
-        }
-    }
-
-    /// Convert this atom into an addrefed nsIAtom pointer.
-    #[inline]
-    pub fn into_addrefed(self) -> *mut nsIAtom {
-        let ptr = self.as_ptr();
-        mem::forget(self);
-        ptr
-    }
-
     /// Return whether two atoms are ASCII-case-insensitive matches
     pub fn eq_ignore_ascii_case(&self, other: &Self) -> bool {
         let a = self.as_slice();
@@ -358,3 +340,19 @@ impl From<*mut nsIAtom> for Atom {
         }
     }
 }
+
+impl From<already_AddRefed<nsIAtom>> for Atom {
+    #[inline]
+    fn from(ptr: already_AddRefed<nsIAtom>) -> Atom {
+        unsafe { Atom(WeakAtom::new(ptr.take())) }
+    }
+}
+
+impl From<Atom> for already_AddRefed<nsIAtom> {
+    #[inline]
+    fn from(atom: Atom) -> already_AddRefed<nsIAtom> {
+        let ptr = atom.as_ptr();
+        mem::forget(atom);
+        unsafe { already_AddRefed::new_unchecked(ptr) }
+    }
+}