Implement the incumbent global.

Fixes #10963.

components/script/dom/bindings/callback.rs

@@ -5,9 +5,9 @@
 //! Base classes to work with IDL callbacks.
 
 use dom::bindings::error::{Error, Fallible, report_pending_exception};
-use dom::bindings::js::{Root, MutHeapJSVal};
+use dom::bindings::js::{JS, Root, MutHeapJSVal};
 use dom::bindings::reflector::DomObject;
-use dom::bindings::settings_stack::AutoEntryScript;
+use dom::bindings::settings_stack::{AutoEntryScript, AutoIncumbentScript};
 use dom::globalscope::GlobalScope;
 use js::jsapi::{Heap, MutableHandleObject};
 use js::jsapi::{IsCallable, JSContext, JSObject, JS_WrapObject, AddRawValueRoot};
@@ -18,6 +18,7 @@ use js::jsval::{JSVal, UndefinedValue, ObjectValue};
 use std::default::Default;
 use std::ffi::CString;
 use std::mem::drop;
+use std::ops::Deref;
 use std::ptr;
 use std::rc::Rc;
 
@@ -30,7 +31,6 @@ pub enum ExceptionHandling {
     Rethrow,
 }
 
-
 /// A common base class for representing IDL callback function and
 /// callback interface types.
 #[derive(JSTraceable)]
@@ -39,6 +39,19 @@ pub struct CallbackObject {
     /// The underlying `JSObject`.
     callback: Heap<*mut JSObject>,
     permanent_js_root: MutHeapJSVal,
+
+    /// The ["callback context"], that is, the global to use as incumbent
+    /// global when calling the callback.
+    ///
+    /// Looking at the WebIDL standard, it appears as though there would always
+    /// be a value here, but [sometimes] callback functions are created by
+    /// hand-waving without defining the value of the callback context, and
+    /// without any JavaScript code on the stack to grab an incumbent global
+    /// from.
+    ///
+    /// ["callback context"]: https://heycam.github.io/webidl/#dfn-callback-context
+    /// [sometimes]: https://github.com/whatwg/html/issues/2248
+    incumbent: Option<JS<GlobalScope>>
 }
 
 impl Default for CallbackObject {
@@ -54,6 +67,7 @@ impl CallbackObject {
         CallbackObject {
             callback: Heap::default(),
             permanent_js_root: MutHeapJSVal::new(),
+            incumbent: GlobalScope::incumbent().map(|i| JS::from_ref(&*i)),
         }
     }
 
@@ -99,6 +113,13 @@ pub trait CallbackContainer {
     fn callback(&self) -> *mut JSObject {
         self.callback_holder().get()
     }
+    /// Returns the ["callback context"], that is, the global to use as
+    /// incumbent global when calling the callback.
+    ///
+    /// ["callback context"]: https://heycam.github.io/webidl/#dfn-callback-context
+    fn incumbent(&self) -> Option<&GlobalScope> {
+        self.callback_holder().incumbent.as_ref().map(JS::deref)
+    }
 }
 
 
@@ -210,6 +231,9 @@ pub struct CallSetup {
     /// https://heycam.github.io/webidl/#es-invoking-callback-functions
     /// steps 8 and 18.2.
     entry_script: Option<AutoEntryScript>,
+    /// https://heycam.github.io/webidl/#es-invoking-callback-functions
+    /// steps 9 and 18.1.
+    incumbent_script: Option<AutoIncumbentScript>,
 }
 
 impl CallSetup {
@@ -222,12 +246,14 @@ impl CallSetup {
         let cx = global.get_cx();
 
         let aes = AutoEntryScript::new(&global);
+        let ais = callback.incumbent().map(AutoIncumbentScript::new);
         CallSetup {
             exception_global: global,
             cx: cx,
             old_compartment: unsafe { JS_EnterCompartment(cx, callback.callback()) },
             handling: handling,
             entry_script: Some(aes),
+            incumbent_script: ais,
         }
     }
 
@@ -246,6 +272,7 @@ impl Drop for CallSetup {
                                                  self.exception_global.reflector().get_jsobject().get());
                 report_pending_exception(self.cx, true);
             }
+            drop(self.incumbent_script.take());
             drop(self.entry_script.take().unwrap());
         }
     }

components/script/dom/bindings/settings_stack.rs

@@ -5,15 +5,26 @@
 use dom::bindings::js::{JS, Root};
 use dom::bindings::trace::JSTraceable;
 use dom::globalscope::GlobalScope;
+use js::jsapi::GetScriptedCallerGlobal;
+use js::jsapi::HideScriptedCaller;
 use js::jsapi::JSTracer;
+use js::jsapi::UnhideScriptedCaller;
+use js::rust::Runtime;
 use std::cell::RefCell;
 
 thread_local!(static STACK: RefCell<Vec<StackEntry>> = RefCell::new(Vec::new()));
 
+#[derive(PartialEq, Eq, Debug, JSTraceable)]
+enum StackEntryKind {
+    Incumbent,
+    Entry,
+}
+
 #[allow(unrooted_must_root)]
 #[derive(JSTraceable)]
 struct StackEntry {
     global: JS<GlobalScope>,
+    kind: StackEntryKind,
 }
 
 /// Traces the script settings stack.
@@ -36,6 +47,7 @@ impl AutoEntryScript {
             let mut stack = stack.borrow_mut();
             stack.push(StackEntry {
                 global: JS::from_ref(global),
+                kind: StackEntryKind::Entry,
             });
             AutoEntryScript {
                 global: global as *const _ as usize,
@@ -53,6 +65,7 @@ impl Drop for AutoEntryScript {
             assert_eq!(&*entry.global as *const GlobalScope as usize,
                        self.global,
                        "Dropped AutoEntryScript out of order.");
+            assert_eq!(entry.kind, StackEntryKind::Entry);
             trace!("Clean up after running script with {:p}", &*entry.global);
         })
     }
@@ -64,7 +77,88 @@ impl Drop for AutoEntryScript {
 pub fn entry_global() -> Root<GlobalScope> {
     STACK.with(|stack| {
         stack.borrow()
-             .last()
+             .iter()
+             .rev()
+             .find(|entry| entry.kind == StackEntryKind::Entry)
              .map(|entry| Root::from_ref(&*entry.global))
     }).unwrap()
 }
+
+/// RAII struct that pushes and pops entries from the script settings stack.
+pub struct AutoIncumbentScript {
+    global: usize,
+}
+
+impl AutoIncumbentScript {
+    /// https://html.spec.whatwg.org/multipage/#prepare-to-run-a-callback
+    pub fn new(global: &GlobalScope) -> Self {
+        // Step 2-3.
+        unsafe {
+            let cx = Runtime::get();
+            assert!(!cx.is_null());
+            HideScriptedCaller(cx);
+        }
+        STACK.with(|stack| {
+            trace!("Prepare to run a callback with {:p}", global);
+            // Step 1.
+            let mut stack = stack.borrow_mut();
+            stack.push(StackEntry {
+                global: JS::from_ref(global),
+                kind: StackEntryKind::Incumbent,
+            });
+            AutoIncumbentScript {
+                global: global as *const _ as usize,
+            }
+        })
+    }
+}
+
+impl Drop for AutoIncumbentScript {
+    /// https://html.spec.whatwg.org/multipage/#clean-up-after-running-a-callback
+    fn drop(&mut self) {
+        STACK.with(|stack| {
+            // Step 4.
+            let mut stack = stack.borrow_mut();
+            let entry = stack.pop().unwrap();
+            // Step 3.
+            assert_eq!(&*entry.global as *const GlobalScope as usize,
+                       self.global,
+                       "Dropped AutoIncumbentScript out of order.");
+            assert_eq!(entry.kind, StackEntryKind::Incumbent);
+            trace!("Clean up after running a callback with {:p}", &*entry.global);
+        });
+        unsafe {
+            // Step 1-2.
+            let cx = Runtime::get();
+            assert!(!cx.is_null());
+            UnhideScriptedCaller(cx);
+        }
+    }
+}
+
+/// Returns the ["incumbent"] global object.
+///
+/// ["incumbent"]: https://html.spec.whatwg.org/multipage/#incumbent
+pub fn incumbent_global() -> Option<Root<GlobalScope>> {
+    // https://html.spec.whatwg.org/multipage/#incumbent-settings-object
+
+    // Step 1, 3: See what the JS engine has to say. If we've got a scripted
+    // caller override in place, the JS engine will lie to us and pretend that
+    // there's nothing on the JS stack, which will cause us to check the
+    // incumbent script stack below.
+    unsafe {
+        let cx = Runtime::get();
+        assert!(!cx.is_null());
+        let global = GetScriptedCallerGlobal(cx);
+        if !global.is_null() {
+            return Some(GlobalScope::from_object(global));
+        }
+    }
+
+    // Step 2: nothing from the JS engine. Let's use whatever's on the explicit stack.
+    STACK.with(|stack| {
+        stack.borrow()
+             .last()
+             .map(|entry| Root::from_ref(&*entry.global))
+    })
+}

components/script/dom/globalscope.rs

@@ -10,7 +10,7 @@ use dom::bindings::error::{ErrorInfo, report_pending_exception};
 use dom::bindings::inheritance::Castable;
 use dom::bindings::js::{MutNullableJS, Root};
 use dom::bindings::reflector::DomObject;
-use dom::bindings::settings_stack::{AutoEntryScript, entry_global};
+use dom::bindings::settings_stack::{AutoEntryScript, entry_global, incumbent_global};
 use dom::bindings::str::DOMString;
 use dom::crypto::Crypto;
 use dom::dedicatedworkerglobalscope::DedicatedWorkerGlobalScope;
@@ -528,6 +528,13 @@ impl GlobalScope {
     pub fn entry() -> Root<Self> {
         entry_global()
     }
+
+    /// Returns the ["incumbent"] global object.
+    ///
+    /// ["incumbent"]: https://html.spec.whatwg.org/multipage/#incumbent
+    pub fn incumbent() -> Option<Root<Self>> {
+        incumbent_global()
+    }
 }
 
 fn timestamp_in_ms(time: Timespec) -> u64 {

components/script/dom/testbinding.rs

@@ -777,6 +777,9 @@ impl TestBindingMethods for TestBinding {
     fn EntryGlobal(&self) -> Root<GlobalScope> {
         GlobalScope::entry()
     }
+    fn IncumbentGlobal(&self) -> Root<GlobalScope> {
+        GlobalScope::incumbent().unwrap()
+    }
 }
 
 impl TestBinding {

components/script/dom/webidls/TestBinding.webidl

@@ -524,6 +524,7 @@ interface TestBinding {
   void panic();
 
   GlobalScope entryGlobal();
+  GlobalScope incumbentGlobal();
 };
 
 callback SimpleCallback = void(any value);

tests/wpt/mozilla/tests/mozilla/globals/entry.html

@@ -5,12 +5,20 @@
 <script src="/resources/testharnessreport.js"></script>
 <script>
 var entry_test = async_test("Entry global");
+var incumbent_test = async_test("Incumbent global");
 var loaded = function() {
   entry_test.step(function() {
     var entry = document.querySelector("#incumbent").contentWindow.get_entry();
     assert_equals(entry, window);
   });
   entry_test.done();
+
+  incumbent_test.step(function() {
+    var expected_incumbent = document.querySelector("#incumbent").contentWindow;
+    var incumbent = expected_incumbent.get_incumbent();
+    assert_equals(incumbent, expected_incumbent);
+  });
+  incumbent_test.done();
 }
 </script>
 <iframe id="incumbent" src="incumbent.html" onload="loaded()"></iframe>

tests/wpt/mozilla/tests/mozilla/globals/incumbent.html

@@ -10,4 +10,11 @@ function get_entry() {
 
   return current.TestBinding.prototype.entryGlobal.call(new relevant.TestBinding());
 }
+
+function get_incumbent() {
+  var current = document.querySelector("#current").contentWindow;
+  var relevant = document.querySelector("#relevant").contentWindow;
+
+  return current.TestBinding.prototype.incumbentGlobal.call(new relevant.TestBinding());
+}
 </script>