Add DiscardOnDrop and make Promise::done auto-cancel on drop (#127)

Cargo.toml

@@ -14,6 +14,7 @@ description = "A standard library for the client-side Web"
 build = "build.rs"
 
 [dependencies]
+discard = "1.0.3"
 serde = { version = "1", optional = true }
 serde_json = { version = "1", optional = true }
 futures = { version = "0.1.18", optional = true }

src/lib.rs

@@ -141,6 +141,8 @@ extern crate futures;
 #[macro_use]
 extern crate stdweb_derive;
 
+extern crate discard;
+
 #[macro_use]
 mod webcore;
 mod webapi;
@@ -173,8 +175,10 @@ pub use webcore::instance_of::InstanceOf;
 pub use webcore::reference_type::ReferenceType;
 pub use webcore::serialization::JsSerialize;
 
+pub use webcore::discard::DiscardOnDrop;
+
 #[cfg(feature = "experimental_features_which_may_break_on_minor_version_bumps")]
-pub use webcore::promise::Promise;
+pub use webcore::promise::{Promise, DoneHandle};
 
 #[cfg(all(
     feature = "futures",

src/webapi/event_target.rs

@@ -20,18 +20,16 @@ impl fmt::Debug for EventListenerHandle {
 }
 
 impl EventListenerHandle {
-    /// Removes the handler from the [IEventTarget](trait.IEventTarget.html) on
+    /// Removes the listener from the [IEventTarget](trait.IEventTarget.html) on
     /// which it was previously registered.
     ///
     /// [(JavaScript docs)](https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/removeEventListener)
     // https://dom.spec.whatwg.org/#ref-for-dom-eventtarget-removeeventlistener%E2%91%A0
     pub fn remove( self ) {
         js! { @(no_return)
-            var self = @{self.reference};
-            var event_type = @{self.event_type};
-            var listener = @{self.listener_reference};
+            var listener = @{&self.listener_reference};
+            @{&self.reference}.removeEventListener( @{self.event_type}, listener );
             listener.drop();
-            self.removeEventListener( event_type, listener );
         }
     }
 }
@@ -42,7 +40,7 @@ impl EventListenerHandle {
 /// [(JavaScript docs)](https://developer.mozilla.org/en-US/docs/Web/API/EventTarget)
 // https://dom.spec.whatwg.org/#eventtarget
 pub trait IEventTarget: ReferenceType {
-    /// Adds given event handler to the list the list of event listeners for
+    /// Adds given event handler to the list of event listeners for
     /// the specified `EventTarget` on which it's called.
     ///
     /// [(JavaScript docs)](https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener)
@@ -51,6 +49,7 @@ pub trait IEventTarget: ReferenceType {
         where T: ConcreteEvent, F: FnMut( T ) + 'static
     {
         let reference = self.as_ref();
+
         let listener_reference = js! {
             var listener = @{listener};
             @{reference}.addEventListener( @{T::EVENT_TYPE}, listener );

src/webapi/mutation_observer.rs

@@ -171,7 +171,7 @@ impl std::ops::Deref for MutationObserverHandle {
     type Target = MutationObserver;
 
     #[inline]
-    fn deref(&self) -> &Self::Target {
+    fn deref( &self ) -> &Self::Target {
         &self.mutation_observer
     }
 }

src/webapi/window.rs

@@ -16,12 +16,12 @@ impl RequestAnimationFrameHandle {
     /// Cancels an animation frame request.
     ///
     /// [(Javascript docs)](https://developer.mozilla.org/en-US/docs/Web/API/Window/cancelAnimationFrame)
-    pub fn cancel(self) {
-        js!{
-            var val = @{self.0};
+    pub fn cancel( self ) {
+        js! { @(no_return)
+            var val = @{&self.0};
             val.window.cancelAnimationFrame(val.request);
             val.callback.drop();
-        };
+        }
     }
 }
 

src/webcore/discard.rs

@@ -0,0 +1,160 @@
+use discard;
+use discard::Discard;
+use std::ops::{Deref, DerefMut};
+
+
+/// If you have a value which implements [`Discard`](https://docs.rs/discard/%5E1.0.3/discard/trait.Discard.html), you can use
+/// [`DiscardOnDrop::new(value)`](struct.DiscardOnDrop.html#method.new) which will wrap the value.
+/// When the wrapper is dropped it will automatically call [`value.discard()`](https://docs.rs/discard/%5E1.0.3/discard/trait.Discard.html#tymethod.discard).
+///
+/// You can use the [`leak`](#method.leak) method to unwrap it (which returns `value`). This causes
+/// it to no longer call [`discard`](https://docs.rs/discard/%5E1.0.3/discard/trait.Discard.html#tymethod.discard) when it is dropped, which
+/// means it will usually leak memory unless you manually call [`discard`](https://docs.rs/discard/%5E1.0.3/discard/trait.Discard.html#tymethod.discard).
+#[must_use = "
+
+     The DiscardOnDrop is unused, which causes it to be immediately discarded.
+     You probably don't want that to happen.
+
+     How to fix this:
+
+       * Store the DiscardOnDrop in a variable or data structure.
+
+       * Or use the leak() method which will cause it to not be
+         discarded (this will usually leak memory!)
+
+     See the documentation for more details.
+"]
+#[derive(Debug)]
+pub struct DiscardOnDrop< A: Discard >( discard::DiscardOnDrop< A > );
+
+impl< A: Discard > DiscardOnDrop< A > {
+    /// Creates a new `DiscardOnDrop`.
+    ///
+    /// When the `DiscardOnDrop` is dropped it will automatically call [`discarder.discard()`](https://docs.rs/discard/%5E1.0.3/discard/trait.Discard.html#tymethod.discard).
+    #[inline]
+    pub fn new( discarder: A ) -> Self {
+        DiscardOnDrop( discard::DiscardOnDrop::new( discarder ) )
+    }
+
+    /// Returns the wrapped `discarder`.
+    ///
+    /// It will no longer automatically call [`discarder.discard()`](https://docs.rs/discard/%5E1.0.3/discard/trait.Discard.html#tymethod.discard), so this will usually leak
+    /// memory unless you manually call [`discarder.discard()`](https://docs.rs/discard/%5E1.0.3/discard/trait.Discard.html#tymethod.discard).
+    #[inline]
+    pub fn leak( self ) -> A {
+        discard::DiscardOnDrop::leak( self.0 )
+    }
+}
+
+impl< A: Discard > Deref for DiscardOnDrop< A > {
+    type Target = A;
+
+    #[inline]
+    fn deref( &self ) -> &Self::Target {
+        &*self.0
+    }
+}
+
+impl< A: Discard > DerefMut for DiscardOnDrop< A > {
+    #[inline]
+    fn deref_mut( &mut self ) -> &mut Self::Target {
+        &mut *self.0
+    }
+}
+
+
+#[cfg(test)]
+mod tests {
+    use discard::Discard;
+    use super::DiscardOnDrop;
+    use std::rc::Rc;
+    use std::cell::Cell;
+
+    struct Foo( Rc< Cell< bool > > );
+
+    impl Foo {
+        fn new() -> Self {
+            Foo( Rc::new( Cell::new( false ) ) )
+        }
+
+        fn dropped( &self ) -> Rc< Cell< bool > > {
+            self.0.clone()
+        }
+
+        fn as_mut( &mut self ) -> &mut Self {
+            self
+        }
+    }
+
+    impl Discard for Foo {
+        fn discard( self ) {
+            self.0.set( true );
+        }
+    }
+
+
+    #[test]
+    fn unused() {
+        Foo::new();
+    }
+
+    #[test]
+    fn unused_discard_on_drop() {
+        DiscardOnDrop::new( Foo::new() );
+    }
+
+    #[test]
+    fn discard() {
+        let foo = Foo::new();
+
+        let dropped = foo.dropped();
+
+        assert_eq!( dropped.get(), false );
+        foo.discard();
+        assert_eq!( dropped.get(), true );
+    }
+
+    #[test]
+    fn no_discard() {
+        let foo = Foo::new();
+
+        let dropped = foo.dropped();
+
+        assert_eq!( dropped.get(), false );
+        drop( foo );
+        assert_eq!( dropped.get(), false );
+    }
+
+    #[test]
+    fn discard_on_drop() {
+        let foo = DiscardOnDrop::new( Foo::new() );
+
+        let dropped = foo.dropped();
+
+        assert_eq!( dropped.get(), false );
+        drop( foo );
+        assert_eq!( dropped.get(), true );
+    }
+
+    #[test]
+    fn leak() {
+        let foo = DiscardOnDrop::new(Foo::new());
+
+        let dropped = foo.dropped();
+
+        assert_eq!( dropped.get(), false );
+        drop( foo.leak() );
+        assert_eq!( dropped.get(), false );
+    }
+
+    #[test]
+    fn deref_mut() {
+        let mut foo = DiscardOnDrop::new( Foo::new() );
+
+        let dropped = foo.as_mut().dropped();
+
+        assert_eq!( dropped.get(), false );
+        drop( foo.leak() );
+        assert_eq!( dropped.get(), false );
+    }
+}

src/webcore/mod.rs

@@ -17,6 +17,7 @@ pub mod once;
 pub mod instance_of;
 pub mod reference_type;
 pub mod promise;
+pub mod discard;
 
 #[cfg(feature = "futures")]
 pub mod promise_future;