Issue #1322 - Part 3: Remove DOM promise interface gunk

Based on work by Boris Zbarsky

9 files changed, 284 insertions, 283 deletions

diff --git a/dom/bindings/Bindings.conf b/dom/bindings/Bindings.conf
index 6f9733c5f..b00af2085 100644
--- a/dom/bindings/Bindings.conf
+++ b/dom/bindings/Bindings.conf
@@ -694,10 +694,6 @@ DOMInterfaces = {
     'headerFile': 'nsGeolocation.h'
 },
 
-'Promise': {
-    'implicitJSContext': [ 'then', 'catch' ],
-},
-
 'PromiseDebugging': {
     'concrete': False,
 },
diff --git a/dom/bindings/Codegen.py b/dom/bindings/Codegen.py
index 9cde82df9..6b23e8225 100644
--- a/dom/bindings/Codegen.py
+++ b/dom/bindings/Codegen.py
@@ -1135,6 +1135,12 @@ class CGHeaders(CGWrapper):
                     declareIncludes.add("mozilla/dom/Date.h")
                 else:
                     bindingHeaders.add("mozilla/dom/Date.h")
+            elif unrolled.isPromise():
+                # See comment in the isInterface() case for why we add
+                # Promise.h to headerSet, not bindingHeaders.
+                headerSet.add("mozilla/dom/Promise.h")
+                # We need ToJSValue to do the Promise to JS conversion.
+                bindingHeaders.add("mozilla/dom/ToJSValue.h")
             elif unrolled.isInterface():
                 if unrolled.isSpiderMonkeyInterface():
                     bindingHeaders.add("jsfriendapi.h")
@@ -1352,7 +1358,11 @@ def UnionTypes(unionTypes, config):
                     headers.add("mozilla/dom/Nullable.h")
                 isSequence = f.isSequence()
                 f = f.unroll()
-                if f.isInterface():
+                if f.isPromise():
+                    headers.add("mozilla/dom/Promise.h")
+                    # We need ToJSValue to do the Promise to JS conversion.
+                    headers.add("mozilla/dom/ToJSValue.h")
+                elif f.isInterface():
                     if f.isSpiderMonkeyInterface():
                         headers.add("jsfriendapi.h")
                         headers.add("mozilla/dom/TypedArray.h")
@@ -1434,7 +1444,11 @@ def UnionConversions(unionTypes, config):
 
             def addHeadersForType(f):
                 f = f.unroll()
-                if f.isInterface():
+                if f.isPromise():
+                    headers.add("mozilla/dom/Promise.h")
+                    # We need ToJSValue to do the Promise to JS conversion.
+                    headers.add("mozilla/dom/ToJSValue.h")
+                elif f.isInterface():
                     if f.isSpiderMonkeyInterface():
                         headers.add("jsfriendapi.h")
                         headers.add("mozilla/dom/TypedArray.h")
@@ -5227,6 +5241,139 @@ def getJSToNativeConversionInfo(type, descriptorProvider, failureCode=None,
                                         holderArgs=holderArgs,
                                         dealWithOptional=isOptional and (not nullable or isOwningUnion))
 
+    if type.isPromise():
+        assert not type.nullable()
+        assert defaultValue is None
+
+        # We always have to hold a strong ref to Promise here, because
+        # Promise::resolve returns an addrefed thing.
+        argIsPointer = isCallbackReturnValue
+        if argIsPointer:
+            declType = CGGeneric("RefPtr<Promise>")
+        else:
+            declType = CGGeneric("OwningNonNull<Promise>")
+
+        # Per spec, what we're supposed to do is take the original
+        # Promise.resolve and call it with the original Promise as this
+        # value to make a Promise out of whatever value we actually have
+        # here.  The question is which global we should use.  There are
+        # several cases to consider:
+        #
+        # 1) Normal call to API with a Promise argument.  This is a case the
+        #    spec covers, and we should be using the current Realm's
+        #    Promise.  That means the current compartment.
+        # 2) Call to API with a Promise argument over Xrays.  In practice,
+        #    this sort of thing seems to be used for giving an API
+        #    implementation a way to wait for conclusion of an asyc
+        #    operation, _not_ to expose the Promise to content code.  So we
+        #    probably want to allow callers to use such an API in a
+        #    "natural" way, by passing chrome-side promises; indeed, that
+        #    may be all that the caller has to represent their async
+        #    operation.  That means we really need to do the
+        #    Promise.resolve() in the caller (chrome) compartment: if we do
+        #    it in the content compartment, we will try to call .then() on
+        #    the chrome promise while in the content compartment, which will
+        #    throw and we'll just get a rejected Promise.  Note that this is
+        #    also the reason why a caller who has a chrome Promise
+        #    representing an async operation can't itself convert it to a
+        #    content-side Promise (at least not without some serious
+        #    gyrations).
+        # 3) Promise return value from a callback or callback interface.
+        #    Per spec, this should use the Realm of the callback object.  In
+        #    our case, that's the compartment of the underlying callback,
+        #    not the current compartment (which may be the compartment of
+        #    some cross-compartment wrapper around said callback).
+        # 4) Return value from a JS-implemented interface.  In this case we
+        #    have a problem.  Our current compartment is the compartment of
+        #    the JS implementation.  But if the JS implementation returned
+        #    a page-side Promise (which is a totally sane thing to do, and
+        #    in fact the right thing to do given that this return value is
+        #    going right to content script) then we don't want to
+        #    Promise.resolve with our current compartment Promise, because
+        #    that will wrap it up in a chrome-side Promise, which is
+        #    decidedly _not_ what's desired here.  So in that case we
+        #    should really unwrap the return value and use the global of
+        #    the result.  CheckedUnwrap should be good enough for that; if
+        #    it fails, then we're failing unwrap while in a
+        #    system-privileged compartment, so presumably we have a dead
+        #    object wrapper.  Just error out.  Do NOT fall back to using
+        #    the current compartment instead: that will return a
+        #    system-privileged rejected (because getting .then inside
+        #    resolve() failed) Promise to the caller, which they won't be
+        #    able to touch.  That's not helpful.  If we error out, on the
+        #    other hand, they will get a content-side rejected promise.
+        #    Same thing if the value returned is not even an object.
+        if isCallbackReturnValue == "JSImpl":
+            # Case 4 above.  Note that globalObj defaults to the current
+            # compartment global.  Note that we don't use $*{exceptionCode}
+            # here because that will try to aRv.Throw(NS_ERROR_UNEXPECTED)
+            # which we don't really want here.
+            assert exceptionCode == "aRv.Throw(NS_ERROR_UNEXPECTED);\nreturn nullptr;\n"
+            getPromiseGlobal = fill(
+                """
+                if (!$${val}.isObject()) {
+                  aRv.ThrowTypeError<MSG_NOT_OBJECT>(NS_LITERAL_STRING("${sourceDescription}"));
+                  return nullptr;
+                }
+                JSObject* unwrappedVal = js::CheckedUnwrap(&$${val}.toObject());
+                if (!unwrappedVal) {
+                  // A slight lie, but not much of one, for a dead object wrapper.
+                  aRv.ThrowTypeError<MSG_NOT_OBJECT>(NS_LITERAL_STRING("${sourceDescription}"));
+                  return nullptr;
+                }
+                globalObj = js::GetGlobalForObjectCrossCompartment(unwrappedVal);
+                """,
+                sourceDescription=sourceDescription)
+        elif isCallbackReturnValue == "Callback":
+            getPromiseGlobal = dedent(
+                """
+                // We basically want our entry global here.  Play it safe
+                // and use GetEntryGlobal() to get it, with whatever
+                // principal-clamping it ends up doing.
+                globalObj = GetEntryGlobal()->GetGlobalJSObject();
+                """)
+        else:
+            getPromiseGlobal = ""
+
+        templateBody = fill(
+            """
+            { // Scope for our GlobalObject, FastErrorResult, JSAutoCompartment,
+              // etc.
+
+              JS::Rooted<JSObject*> globalObj(cx, JS::CurrentGlobalOrNull(cx));
+              $*{getPromiseGlobal}
+              JSAutoCompartment ac(cx, globalObj);
+              GlobalObject promiseGlobal(cx, globalObj);
+              if (promiseGlobal.Failed()) {
+                $*{exceptionCode}
+              }
+
+              JS::Rooted<JS::Value> valueToResolve(cx, $${val});
+              if (!JS_WrapValue(cx, &valueToResolve)) {
+                $*{exceptionCode}
+              }
+              binding_detail::FastErrorResult promiseRv;
+              nsCOMPtr<nsIGlobalObject> global =
+                do_QueryInterface(promiseGlobal.GetAsSupports());
+              if (!global) {
+                promiseRv.Throw(NS_ERROR_UNEXPECTED);
+                promiseRv.MaybeSetPendingException(cx);
+                $*{exceptionCode}
+              }
+              $${declName} = Promise::Resolve(global, cx, valueToResolve,
+                                              promiseRv);
+              if (promiseRv.MaybeSetPendingException(cx)) {
+                $*{exceptionCode}
+              }
+            }
+            """,
+            getPromiseGlobal=getPromiseGlobal,
+            exceptionCode=exceptionCode)
+
+        return JSToNativeConversionInfo(templateBody,
+                                        declType=declType,
+                                        dealWithOptional=isOptional)
+
     if type.isGeckoInterface():
         assert not isEnforceRange and not isClamp
 
@@ -5265,12 +5412,8 @@ def getJSToNativeConversionInfo(type, descriptorProvider, failureCode=None,
         # Also, callback return values always end up addrefing anyway, so there
         # is no point trying to avoid it here and it makes other things simpler
         # since we can assume the return value is a strong ref.
-        #
-        # Finally, promises need to hold a strong ref because that's what
-        # Promise.resolve returns.
         assert not descriptor.interface.isCallback()
-        isPromise = descriptor.interface.identifier.name == "Promise"
-        forceOwningType = isMember or isCallbackReturnValue or isPromise
+        forceOwningType = isMember or isCallbackReturnValue
 
         typeName = descriptor.nativeType
         typePtr = typeName + "*"
@@ -5298,122 +5441,8 @@ def getJSToNativeConversionInfo(type, descriptorProvider, failureCode=None,
         if forceOwningType:
             templateBody += 'static_assert(IsRefcounted<%s>::value, "We can only store refcounted classes.");' % typeName
 
-        if isPromise:
-            # Per spec, what we're supposed to do is take the original
-            # Promise.resolve and call it with the original Promise as this
-            # value to make a Promise out of whatever value we actually have
-            # here.  The question is which global we should use.  There are
-            # several cases to consider:
-            #
-            # 1) Normal call to API with a Promise argument.  This is a case the
-            #    spec covers, and we should be using the current Realm's
-            #    Promise.  That means the current compartment.
-            # 2) Call to API with a Promise argument over Xrays.  In practice,
-            #    this sort of thing seems to be used for giving an API
-            #    implementation a way to wait for conclusion of an asyc
-            #    operation, _not_ to expose the Promise to content code.  So we
-            #    probably want to allow callers to use such an API in a
-            #    "natural" way, by passing chrome-side promises; indeed, that
-            #    may be all that the caller has to represent their async
-            #    operation.  That means we really need to do the
-            #    Promise.resolve() in the caller (chrome) compartment: if we do
-            #    it in the content compartment, we will try to call .then() on
-            #    the chrome promise while in the content compartment, which will
-            #    throw and we'll just get a rejected Promise.  Note that this is
-            #    also the reason why a caller who has a chrome Promise
-            #    representing an async operation can't itself convert it to a
-            #    content-side Promise (at least not without some serious
-            #    gyrations).
-            # 3) Promise return value from a callback or callback interface.
-            #    This is in theory a case the spec covers but in practice it
-            #    really doesn't define behavior here because it doesn't define
-            #    what Realm we're in after the callback returns, which is when
-            #    the argument conversion happens.  We will use the current
-            #    compartment, which is the compartment of the callable (which
-            #    may itself be a cross-compartment wrapper itself), which makes
-            #    as much sense as anything else. In practice, such an API would
-            #    once again be providing a Promise to signal completion of an
-            #    operation, which would then not be exposed to anyone other than
-            #    our own implementation code.
-            # 4) Return value from a JS-implemented interface.  In this case we
-            #    have a problem.  Our current compartment is the compartment of
-            #    the JS implementation.  But if the JS implementation returned
-            #    a page-side Promise (which is a totally sane thing to do, and
-            #    in fact the right thing to do given that this return value is
-            #    going right to content script) then we don't want to
-            #    Promise.resolve with our current compartment Promise, because
-            #    that will wrap it up in a chrome-side Promise, which is
-            #    decidedly _not_ what's desired here.  So in that case we
-            #    should really unwrap the return value and use the global of
-            #    the result.  CheckedUnwrap should be good enough for that; if
-            #    it fails, then we're failing unwrap while in a
-            #    system-privileged compartment, so presumably we have a dead
-            #    object wrapper.  Just error out.  Do NOT fall back to using
-            #    the current compartment instead: that will return a
-            #    system-privileged rejected (because getting .then inside
-            #    resolve() failed) Promise to the caller, which they won't be
-            #    able to touch.  That's not helpful.  If we error out, on the
-            #    other hand, they will get a content-side rejected promise.
-            #    Same thing if the value returned is not even an object.
-            if isCallbackReturnValue == "JSImpl":
-                # Case 4 above.  Note that globalObj defaults to the current
-                # compartment global.  Note that we don't use $*{exceptionCode}
-                # here because that will try to aRv.Throw(NS_ERROR_UNEXPECTED)
-                # which we don't really want here.
-                assert exceptionCode == "aRv.Throw(NS_ERROR_UNEXPECTED);\nreturn nullptr;\n"
-                getPromiseGlobal = fill(
-                    """
-                    if (!$${val}.isObject()) {
-                      aRv.ThrowTypeError<MSG_NOT_OBJECT>(NS_LITERAL_STRING("${sourceDescription}"));
-                      return nullptr;
-                    }
-                    JSObject* unwrappedVal = js::CheckedUnwrap(&$${val}.toObject());
-                    if (!unwrappedVal) {
-                      // A slight lie, but not much of one, for a dead object wrapper.
-                      aRv.ThrowTypeError<MSG_NOT_OBJECT>(NS_LITERAL_STRING("${sourceDescription}"));
-                      return nullptr;
-                    }
-                    globalObj = js::GetGlobalForObjectCrossCompartment(unwrappedVal);
-                    """,
-                    sourceDescription=sourceDescription)
-            else:
-                getPromiseGlobal = ""
-
-            templateBody = fill(
-                """
-                { // Scope for our GlobalObject, FastErrorResult, JSAutoCompartment,
-                  // etc.
-
-                  JS::Rooted<JSObject*> globalObj(cx, JS::CurrentGlobalOrNull(cx));
-                  $*{getPromiseGlobal}
-                  JSAutoCompartment ac(cx, globalObj);
-                  GlobalObject promiseGlobal(cx, globalObj);
-                  if (promiseGlobal.Failed()) {
-                    $*{exceptionCode}
-                  }
-
-                  JS::Rooted<JS::Value> valueToResolve(cx, $${val});
-                  if (!JS_WrapValue(cx, &valueToResolve)) {
-                    $*{exceptionCode}
-                  }
-                  binding_detail::FastErrorResult promiseRv;
-                  nsCOMPtr<nsIGlobalObject> global =
-                    do_QueryInterface(promiseGlobal.GetAsSupports());
-                  if (!global) {
-                    promiseRv.Throw(NS_ERROR_UNEXPECTED);
-                    promiseRv.MaybeSetPendingException(cx);
-                    $*{exceptionCode}
-                  }
-                  $${declName} = Promise::Resolve(global, cx, valueToResolve,
-                                                  promiseRv);
-                  if (promiseRv.MaybeSetPendingException(cx)) {
-                    $*{exceptionCode}
-                  }
-                }
-                """,
-                getPromiseGlobal=getPromiseGlobal,
-                exceptionCode=exceptionCode)
-        elif not descriptor.interface.isConsequential() and not descriptor.interface.isExternal():
+        if (not descriptor.interface.isConsequential() and
+            not descriptor.interface.isExternal()):
             if failureCode is not None:
                 templateBody += str(CastableObjectUnwrapper(
                     descriptor,
@@ -5453,24 +5482,12 @@ def getJSToNativeConversionInfo(type, descriptorProvider, failureCode=None,
             # And store our value in ${declName}
             templateBody += "${declName} = ${holderName};\n"
 
-        if isPromise:
-            if type.nullable():
-                codeToSetNull = "${declName} = nullptr;\n"
-                templateBody = CGIfElseWrapper(
-                    "${val}.isNullOrUndefined()",
-                    CGGeneric(codeToSetNull),
-                    CGGeneric(templateBody)).define()
-                if isinstance(defaultValue, IDLNullValue):
-                    templateBody = handleDefault(templateBody, codeToSetNull)
-            else:
-                assert defaultValue is None
-        else:
-            # Just pass failureCode, not onFailureBadType, here, so we'll report
-            # the thing as not an object as opposed to not implementing whatever
-            # our interface is.
-            templateBody = wrapObjectTemplate(templateBody, type,
-                                              "${declName} = nullptr;\n",
-                                              failureCode)
+        # Just pass failureCode, not onFailureBadType, here, so we'll report
+        # the thing as not an object as opposed to not implementing whatever
+        # our interface is.
+        templateBody = wrapObjectTemplate(templateBody, type,
+                                          "${declName} = nullptr;\n",
+                                          failureCode)
 
         declType = CGGeneric(declType)
         if holderType is not None:
@@ -6537,6 +6554,19 @@ def getWrapTemplateForType(type, descriptorProvider, result, successCode,
 
         return (code, False)
 
+    if type.isPromise():
+        assert not type.nullable()
+        # The use of ToJSValue here is a bit annoying because the Promise
+        # version is not inlined, but we can't put an inline version in either
+        # ToJSValue.h or BindingUtils.h, because Promise.h includes ToJSValue.h
+        # and that includes BindingUtils.h, so we'd get an include loop if
+        # either of those headers included Promise.h. Trying to write the
+        # conversion by hand here is annoying because we'd have to handle
+        # the various RefPtr, rawptr, NonNull, etc. cases, which ToJSValue will
+        # already handle for us, so we just use the function call.
+        return (wrapAndSetPtr("ToJSValue(cx, %s, ${jsvalHandle})" % result),
+                False)
+
     if type.isGeckoInterface() and not type.isCallbackInterface():
         descriptor = descriptorProvider.getDescriptor(type.unroll().inner.identifier.name)
         if type.nullable():
@@ -6551,14 +6581,6 @@ def getWrapTemplateForType(type, descriptorProvider, result, successCode,
                 wrapMethod = "GetOrCreateDOMReflector"
                 wrapArgs = "cx, %s, ${jsvalHandle}" % result
             else:
-                # Hack: the "Promise" interface is OK to return from
-                # non-newobject things even when it's not wrappercached; that
-                # happens when using SpiderMonkey promises, and the WrapObject()
-                # method will just return the existing reflector, which is just
-                # not stored in a wrappercache.
-                if (not returnsNewObject and
-                    descriptor.interface.identifier.name != "Promise"):
-                    raise MethodNotNewObjectError(descriptor.interface.identifier.name)
                 wrapMethod = "WrapNewBindingNonWrapperCachedObject"
                 wrapArgs = "cx, ${obj}, %s, ${jsvalHandle}" % result
             if isConstructorRetval:
@@ -6874,14 +6896,17 @@ def getRetvalDeclarationForType(returnType, descriptorProvider,
         if returnType.nullable():
             result = CGTemplatedType("Nullable", result)
         return result, None, None, None, None
-    if returnType.isGeckoInterface():
-        result = CGGeneric(descriptorProvider.getDescriptor(
-            returnType.unroll().inner.identifier.name).nativeType)
-        conversion = None
+    if returnType.isGeckoInterface() or returnType.isPromise():
+        if returnType.isGeckoInterface():
+            typeName = descriptorProvider.getDescriptor(
+                returnType.unroll().inner.identifier.name).nativeType
+        else:
+            typeName = "Promise"
         if isMember:
-            result = CGGeneric("StrongPtrForMember<%s>::Type" % result.define())
+            conversion = None
+            result = CGGeneric("StrongPtrForMember<%s>::Type" % typeName)
         else:
-            conversion = CGGeneric("StrongOrRawPtr<%s>" % result.define())
+            conversion = CGGeneric("StrongOrRawPtr<%s>" % typeName)
             result = CGGeneric("auto")
         return result, None, None, None, conversion
     if returnType.isCallback():
@@ -7046,7 +7071,9 @@ class CGCallGenerator(CGThing):
             if needsConst(a):
                 arg = CGWrapper(arg, pre="Constify(", post=")")
             # And convert NonNull<T> to T&
-            if (((a.type.isGeckoInterface() or a.type.isCallback()) and not a.type.nullable()) or
+            if (((a.type.isGeckoInterface() or a.type.isCallback() or
+                  a.type.isPromise()) and
+                 not a.type.nullable()) or
                 a.type.isDOMString()):
                 arg = CGWrapper(arg, pre="NonNullHelper(", post=")")
             args.append(arg)
@@ -7170,6 +7197,9 @@ class CGCallGenerator(CGThing):
 
 
 def getUnionMemberName(type):
+    # Promises can't be in unions, because they're not distinguishable
+    # from anything else.
+    assert not type.isPromise()
     if type.isGeckoInterface():
         return type.inner.identifier.name
     if type.isEnum():
@@ -7299,8 +7329,9 @@ def wrapTypeIntoCurrentCompartment(type, value, isMember=True):
         return CGList(memberWraps, "else ") if len(memberWraps) != 0 else None
 
     if (type.isString() or type.isPrimitive() or type.isEnum() or
-        type.isGeckoInterface() or type.isCallback() or type.isDate()):
-        # All of these don't need wrapping
+        type.isGeckoInterface() or type.isCallback() or type.isDate() or
+        type.isPromise()):
+        # All of these don't need wrapping.
         return None
 
     raise TypeError("Unknown type; we don't know how to wrap it in constructor "
@@ -7438,58 +7469,12 @@ class CGPerSignatureCall(CGThing):
         if needsCx:
             argsPre.append("cx")
 
-        # Hack for making Promise.prototype.then work well over Xrays.
-        if (not idlNode.isStatic() and
-            descriptor.name == "Promise" and
-            idlNode.isMethod() and
-            idlNode.identifier.name == "then"):
-            cgThings.append(CGGeneric(dedent(
-                """
-                JS::Rooted<JSObject*> calleeGlobal(cx, xpc::XrayAwareCalleeGlobal(&args.callee()));
-                """)))
-            argsPre.append("calleeGlobal")
-
         needsUnwrap = False
         argsPost = []
         if isConstructor:
-            if descriptor.name == "Promise":
-                # Hack for Promise for now: pass in our desired proto so the
-                # implementation can create the reflector with the right proto.
-                argsPost.append("desiredProto")
-                # Also, we do not want to enter the content compartment when the
-                # Promise constructor is called via Xrays, because we want to
-                # create our callback functions that we will hand to our caller
-                # in the Xray compartment.  The reason we want to do that is the
-                # following situation, over Xrays:
-                #
-                #   contentWindow.Promise.race([Promise.resolve(5)])
-                #
-                # Ideally this would work.  Internally, race() does a
-                # contentWindow.Promise.resolve() on everything in the array.
-                # Per spec, to support subclassing,
-                # contentWindow.Promise.resolve has to do:
-                #
-                #   var resolve, reject;
-                #   var p = new contentWindow.Promise(function(a, b) {
-                #    resolve = a;
-                #    reject = b;
-                #  });
-                #  resolve(arg);
-                #  return p;
-                #
-                # where "arg" is, in this case, the chrome-side return value of
-                # Promise.resolve(5).  But if the "resolve" function in that
-                # case were created in the content compartment, then calling it
-                # would wrap "arg" in an opaque wrapper, and that function tries
-                # to get .then off the argument, which would throw.  So we need
-                # to create the "resolve" function in the chrome compartment,
-                # and hence want to be running the entire Promise constructor
-                # (which creates that function) in the chrome compartment in
-                # this case. So don't set needsUnwrap here.
-            else:
-                needsUnwrap = True
-                needsUnwrappedVar = False
-                unwrappedVar = "obj"
+            needsUnwrap = True
+            needsUnwrappedVar = False
+            unwrappedVar = "obj"
         elif descriptor.interface.isJSImplemented():
             if not idlNode.isStatic():
                 needsUnwrap = True
@@ -7502,11 +7487,6 @@ class CGPerSignatureCall(CGThing):
             needsUnwrappedVar = True
             argsPre.append("unwrappedObj ? *unwrappedObj : obj")
 
-        if idlNode.isStatic() and not isConstructor and descriptor.name == "Promise":
-            # Hack for Promise for now: pass in the "this" value to
-            # Promise static methods.
-            argsPre.append("args.thisv()")
-
         if needsUnwrap and needsUnwrappedVar:
             # We cannot assign into obj because it's a Handle, not a
             # MutableHandle, so we need a separate Rooted.
@@ -7649,7 +7629,8 @@ class CGPerSignatureCall(CGThing):
 
         returnsNewObject = memberReturnsNewObject(self.idlNode)
         if (returnsNewObject and
-            self.returnType.isGeckoInterface()):
+            (self.returnType.isGeckoInterface() or
+             self.returnType.isPromise())):
             wrapCode += dedent(
                 """
                 static_assert(!IsPointer<decltype(result)>::value,
@@ -9455,6 +9436,8 @@ class CGMemberJITInfo(CGThing):
             return "JSVAL_TYPE_OBJECT"
         if t.isRecord():
             return "JSVAL_TYPE_OBJECT"
+        if t.isPromise():
+            return "JSVAL_TYPE_OBJECT"
         if t.isGeckoInterface():
             return "JSVAL_TYPE_OBJECT"
         if t.isString():
@@ -9528,6 +9511,8 @@ class CGMemberJITInfo(CGThing):
             return "JSJitInfo::ArgType(JSJitInfo::Null | %s)" % CGMemberJITInfo.getJSArgType(t.inner)
         if t.isSequence():
             return "JSJitInfo::Object"
+        if t.isPromise():
+            return "JSJitInfo::Object"
         if t.isGeckoInterface():
             return "JSJitInfo::Object"
         if t.isString():
@@ -9714,6 +9699,10 @@ def getUnionAccessorSignatureType(type, descriptorProvider):
     # Flat member types have already unwrapped nullables.
     assert not type.nullable()
 
+    # Promise types can never appear in unions, because Promise is not
+    # distinguishable from anything.
+    assert not type.isPromise()
+
     if type.isSequence() or type.isRecord():
         if type.isSequence():
             wrapperType = "Sequence"
@@ -13622,6 +13611,8 @@ class ForwardDeclarationBuilder:
 
         # Note: Spidermonkey interfaces are typedefs, so can't be
         # forward-declared
+        elif t.isPromise():
+            self.addInMozillaDom("Promise")
         elif t.isCallback():
             self.addInMozillaDom(t.callback.identifier.name)
         elif t.isDictionary():
@@ -14076,10 +14067,13 @@ class CGNativeMember(ClassMethod):
             else:
                 defaultValue = "%s(0)" % enumName
             return enumName, defaultValue, "return ${declName};\n"
-        if type.isGeckoInterface():
-            iface = type.unroll().inner
-            result = CGGeneric(self.descriptorProvider.getDescriptor(
-                iface.identifier.name).prettyNativeType)
+        if type.isGeckoInterface() or type.isPromise():
+            if type.isGeckoInterface():
+                iface = type.unroll().inner
+                result = CGGeneric(self.descriptorProvider.getDescriptor(
+                    iface.identifier.name).prettyNativeType)
+            else:
+                result = CGGeneric("Promise")
             if self.resultAlreadyAddRefed:
                 if isMember:
                     holder = "RefPtr"
@@ -14282,11 +14276,18 @@ class CGNativeMember(ClassMethod):
             # auto-wrapping in Nullable
             return CGUnionStruct.unionTypeDecl(type, isMember), True, False
 
+        if type.isPromise():
+            assert not type.nullable()
+            if optional or isMember:
+                typeDecl = "OwningNonNull<Promise>"
+            else:
+                typeDecl = "Promise&"
+            return (typeDecl, False, False)
+
         if type.isGeckoInterface() and not type.isCallbackInterface():
             iface = type.unroll().inner
             argIsPointer = type.nullable() or iface.isExternal()
-            forceOwningType = (iface.isCallback() or isMember or
-                               iface.identifier.name == "Promise")
+            forceOwningType = (iface.isCallback() or isMember)
             if argIsPointer:
                 if (optional or isMember) and forceOwningType:
                     typeDecl = "RefPtr<%s>"
@@ -16920,7 +16921,10 @@ class CGEventGetter(CGNativeMember):
     def getMethodBody(self):
         type = self.member.type
         memberName = CGDictionary.makeMemberName(self.member.identifier.name)
-        if (type.isPrimitive() and type.tag() in builtinNames) or type.isEnum() or type.isGeckoInterface():
+        if ((type.isPrimitive() and type.tag() in builtinNames) or
+            type.isEnum() or
+            type.isPromise() or
+            type.isGeckoInterface()):
             return "return " + memberName + ";\n"
         if type.isDOMString() or type.isByteString() or type.isUSVString():
             return "aRetVal = " + memberName + ";\n"
@@ -17331,6 +17335,8 @@ class CGEventClass(CGBindingImplClass):
             nativeType = CGGeneric("nsString")
         elif type.isByteString():
             nativeType = CGGeneric("nsCString")
+        elif type.isPromise():
+            nativeType = CGGeneric("RefPtr<Promise>")
         elif type.isGeckoInterface():
             iface = type.unroll().inner
             nativeType = self.descriptor.getDescriptor(
@@ -17355,7 +17361,7 @@ class CGEventClass(CGBindingImplClass):
                 innerType = type.inner
             if (not innerType.isPrimitive() and not innerType.isEnum() and
                 not innerType.isDOMString() and not innerType.isByteString() and
-                not innerType.isGeckoInterface()):
+                not innerType.isPromise() and not innerType.isGeckoInterface()):
                 raise TypeError("Don't know how to properly manage GC/CC for "
                                 "event member of type %s" %
                                 type)
diff --git a/dom/bindings/Configuration.py b/dom/bindings/Configuration.py
index f80c19c33..a56f2f2fd 100644
--- a/dom/bindings/Configuration.py
+++ b/dom/bindings/Configuration.py
@@ -468,13 +468,6 @@ class Descriptor(DescriptorProvider):
         self.wrapperCache = (not self.interface.isCallback() and
                              not self.interface.isIteratorInterface() and
                              desc.get('wrapperCache', True))
-        # Nasty temporary hack for supporting both DOM and SpiderMonkey promises
-        # without too much pain
-        if self.interface.identifier.name == "Promise":
-            assert self.wrapperCache
-            # But really, we're only wrappercached if we have an interface
-            # object (that is, when we're not using SpiderMonkey promises).
-            self.wrapperCache = self.interface.hasInterfaceObject()
 
         self.name = interface.identifier.name
 
diff --git a/dom/bindings/Errors.msg b/dom/bindings/Errors.msg
index 142ccfdd6..c47f75875 100644
--- a/dom/bindings/Errors.msg
+++ b/dom/bindings/Errors.msg
@@ -84,11 +84,6 @@ MSG_DEF(MSG_NOTIFICATION_PERMISSION_DENIED, 0, JSEXN_TYPEERR, "Permission to sho
 MSG_DEF(MSG_NOTIFICATION_NO_CONSTRUCTOR_IN_SERVICEWORKER, 0, JSEXN_TYPEERR, "Notification constructor cannot be used in ServiceWorkerGlobalScope. Use registration.showNotification() instead.")
 MSG_DEF(MSG_INVALID_SCOPE, 2, JSEXN_TYPEERR, "Invalid scope trying to resolve {0} with base URL {1}.")
 MSG_DEF(MSG_INVALID_KEYFRAME_OFFSETS, 0, JSEXN_TYPEERR, "Keyframes with specified offsets must be in order and all be in the range [0, 1].")
-MSG_DEF(MSG_ILLEGAL_PROMISE_CONSTRUCTOR, 0, JSEXN_TYPEERR, "Non-constructor value passed to NewPromiseCapability.")
-MSG_DEF(MSG_PROMISE_CAPABILITY_HAS_SOMETHING_ALREADY, 0, JSEXN_TYPEERR, "GetCapabilitiesExecutor function already invoked with non-undefined values.")
-MSG_DEF(MSG_PROMISE_RESOLVE_FUNCTION_NOT_CALLABLE, 0, JSEXN_TYPEERR, "A Promise subclass passed a non-callable value as the resolve function.")
-MSG_DEF(MSG_PROMISE_REJECT_FUNCTION_NOT_CALLABLE, 0, JSEXN_TYPEERR, "A Promise subclass passed a non-callable value as the reject function.")
-MSG_DEF(MSG_PROMISE_ARG_NOT_ITERABLE, 1, JSEXN_TYPEERR, "{0} is not iterable")
 MSG_DEF(MSG_IS_NOT_PROMISE, 1, JSEXN_TYPEERR, "{0} is not a Promise")
 MSG_DEF(MSG_SW_INSTALL_ERROR, 2, JSEXN_TYPEERR, "ServiceWorker script at {0} for scope {1} encountered an error during installation.")
 MSG_DEF(MSG_SW_SCRIPT_THREW, 2, JSEXN_TYPEERR, "ServiceWorker script at {0} for scope {1} threw an exception during script evaluation.")
diff --git a/dom/bindings/ToJSValue.cpp b/dom/bindings/ToJSValue.cpp
index 19219f432..7afff41e2 100644
--- a/dom/bindings/ToJSValue.cpp
+++ b/dom/bindings/ToJSValue.cpp
@@ -69,7 +69,7 @@ ToJSValue(JSContext* aCx, Promise& aArgument,
           JS::MutableHandle<JS::Value> aValue)
 {
   aValue.setObject(*aArgument.PromiseObj());
-  return true;
+  return MaybeWrapObjectValue(aCx, aValue);
 }
 
 } // namespace dom
diff --git a/dom/bindings/TypedArray.h b/dom/bindings/TypedArray.h
index a86abcd9d..75313e255 100644
--- a/dom/bindings/TypedArray.h
+++ b/dom/bindings/TypedArray.h
@@ -344,7 +344,7 @@ typedef TypedArray<uint8_t, js::UnwrapSharedArrayBuffer, JS_GetSharedArrayBuffer
 // A class for converting an nsTArray to a TypedArray
 // Note: A TypedArrayCreator must not outlive the nsTArray it was created from.
 //       So this is best used to pass from things that understand nsTArray to
-//       things that understand TypedArray, as with Promise::ArgumentToJSValue.
+//       things that understand TypedArray, as with ToJSValue.
 template<typename TypedArrayType>
 class TypedArrayCreator
 {
diff --git a/dom/bindings/parser/WebIDL.py b/dom/bindings/parser/WebIDL.py
index 8c32a8738..fafb3c9b6 100644
--- a/dom/bindings/parser/WebIDL.py
+++ b/dom/bindings/parser/WebIDL.py
@@ -1597,11 +1597,7 @@ class IDLInterface(IDLInterfaceOrNamespace):
 
                 args = attr.args() if attr.hasArgs() else []
 
-                if self.identifier.name == "Promise":
-                    promiseType = BuiltinTypes[IDLBuiltinType.Types.any]
-                else:
-                    promiseType = None
-                retType = IDLWrapperType(self.location, self, promiseType)
+                retType = IDLWrapperType(self.location, self)
 
                 if identifier == "Constructor" or identifier == "ChromeConstructor":
                     name = "constructor"
@@ -1988,7 +1984,8 @@ class IDLType(IDLObject):
         'callback',
         'union',
         'sequence',
-        'record'
+        'record',
+        'promise'
         )
 
     def __init__(self, location, name):
@@ -2142,9 +2139,8 @@ class IDLUnresolvedType(IDLType):
         Unresolved types are interface types
     """
 
-    def __init__(self, location, name, promiseInnerType=None):
+    def __init__(self, location, name):
         IDLType.__init__(self, location, name)
-        self._promiseInnerType = promiseInnerType
 
     def isComplete(self):
         return False
@@ -2171,11 +2167,8 @@ class IDLUnresolvedType(IDLType):
             assert self.name.name == obj.identifier.name
             return IDLCallbackType(self.location, obj)
 
-        if self._promiseInnerType and not self._promiseInnerType.isComplete():
-            self._promiseInnerType = self._promiseInnerType.complete(scope)
-
         name = self.name.resolve(scope, None)
-        return IDLWrapperType(self.location, obj, self._promiseInnerType)
+        return IDLWrapperType(self.location, obj)
 
     def isDistinguishableFrom(self, other):
         raise TypeError("Can't tell whether an unresolved type is or is not "
@@ -2285,7 +2278,9 @@ class IDLNullableType(IDLParameterizedType):
         return self.inner.isInterface()
 
     def isPromise(self):
-        return self.inner.isPromise()
+        # There is no such thing as a nullable Promise.
+        assert not self.inner.isPromise()
+        return False
 
     def isCallbackInterface(self):
         return self.inner.isCallbackInterface()
@@ -2698,13 +2693,11 @@ class IDLTypedef(IDLObjectWithIdentifier):
 
 
 class IDLWrapperType(IDLType):
-    def __init__(self, location, inner, promiseInnerType=None):
+    def __init__(self, location, inner):
         IDLType.__init__(self, location, inner.identifier.name)
         self.inner = inner
         self._identifier = inner.identifier
         self.builtin = False
-        assert not promiseInnerType or inner.identifier.name == "Promise"
-        self._promiseInnerType = promiseInnerType
 
     def __eq__(self, other):
         return (isinstance(other, IDLWrapperType) and
@@ -2754,14 +2747,6 @@ class IDLWrapperType(IDLType):
     def isEnum(self):
         return isinstance(self.inner, IDLEnum)
 
-    def isPromise(self):
-        return (isinstance(self.inner, IDLInterface) and
-                self.inner.identifier.name == "Promise")
-
-    def promiseInnerType(self):
-        assert self.isPromise()
-        return self._promiseInnerType
-
     def isSerializable(self):
         if self.isInterface():
             if self.inner.isExternal():
@@ -2793,8 +2778,6 @@ class IDLWrapperType(IDLType):
             assert False
 
     def isDistinguishableFrom(self, other):
-        if self.isPromise():
-            return False
         if other.isPromise():
             return False
         if other.isUnion():
@@ -2841,10 +2824,6 @@ class IDLWrapperType(IDLType):
             # Let's say true, though ideally we'd only do this when
             # exposureSet contains the primary global's name.
             return True
-        if (self.isPromise() and
-            # Check the internal type
-            not self.promiseInnerType().unroll().isExposedInAllOf(exposureSet)):
-            return False
         return iface.exposureSet.issuperset(exposureSet)
 
     def _getDependentObjects(self):
@@ -2871,6 +2850,45 @@ class IDLWrapperType(IDLType):
             return set([self.inner])
         return set()
 
+

+class IDLPromiseType(IDLParametrizedType):

+    def __init__(self, location, innerType):

+        IDLParametrizedType.__init__(self, location, "Promise", innerType)

+

+    def __eq__(self, other):

+        return (isinstance(other, IDLPromiseType) and

+                self.promiseInnerType() == other.promiseInnerType())

+

+    def __str__(self):

+        return self.inner.__str__() + "Promise"

+

+    def isPromise(self):

+        return True

+

+    def promiseInnerType(self):

+        return self.inner

+

+    def tag(self):

+        return IDLType.Tags.promise

+

+    def complete(self, scope):

+        self.inner = self.promiseInnerType().complete(scope)

+        return self

+

+    def unroll(self):

+        # We do not unroll our inner.  Just stop at ourselves.  That

+        # lets us add headers for both ourselves and our inner as

+        # needed.

+        return self

+

+    def isDistinguishableFrom(self, other):

+        # Promises are not distinguishable from anything.

+        return False

+

+    def isExposedInAllOf(self, exposureSet):

+        # Check the internal type

+        return self.promiseInnerType().unroll().isExposedInAllOf(exposureSet)

+

 
 class IDLBuiltinType(IDLType):
 
@@ -3990,7 +4008,9 @@ class IDLAttribute(IDLInterfaceMember):
             raise WebIDLError("An attribute with [PutForwards] must have an "
                               "interface type as its type", [self.location])
 
-        if not self.type.isInterface() and self.getExtendedAttribute("SameObject"):
+        if (not self.type.isInterface() and
+            not self.type.isPromise() and
+            self.getExtendedAttribute("SameObject")):
             raise WebIDLError("An attribute with [SameObject] must have an "
                               "interface type as its type", [self.location])
 
@@ -6394,17 +6414,13 @@ class Parser(Tokenizer):
         type = IDLSequenceType(self.getLocation(p, 1), innerType)
         p[0] = self.handleNullable(type, p[5])
 
-    # Note: Promise<void> is allowed, so we want to parametrize on
-    # ReturnType, not Type.  Also, we want this to end up picking up
-    # the Promise interface for now, hence the games with IDLUnresolvedType.
+    # Note: Promise<void> is allowed, so we want to parameterize on
+    # ReturnType, not Type. Promise types can't be null, hence no "Null" in there.
     def p_NonAnyTypePromiseType(self, p):
         """
-            NonAnyType : PROMISE LT ReturnType GT Null
+            NonAnyType : PROMISE LT ReturnType GT
         """
-        innerType = p[3]
-        promiseIdent = IDLUnresolvedIdentifier(self.getLocation(p, 1), "Promise")
-        type = IDLUnresolvedType(self.getLocation(p, 1), promiseIdent, p[3])
-        p[0] = self.handleNullable(type, p[5])
+        p[0] = IDLPromiseType(self.getLocation(p, 1), p[3])
 
     def p_NonAnyTypeRecordType(self, p):
         """
diff --git a/dom/bindings/parser/tests/test_distinguishability.py b/dom/bindings/parser/tests/test_distinguishability.py
index d7780c1ff..ac515a01d 100644
--- a/dom/bindings/parser/tests/test_distinguishability.py
+++ b/dom/bindings/parser/tests/test_distinguishability.py
@@ -263,7 +263,6 @@ def WebIDLTest(parser, harness):
           callback Callback2 = long(short arg);
           dictionary Dict {};
           dictionary Dict2 {};
-          interface _Promise {};
           interface TestInterface {%s
           };
         """
diff --git a/dom/bindings/parser/tests/test_promise.py b/dom/bindings/parser/tests/test_promise.py
index 55bc07680..091381fab 100644
--- a/dom/bindings/parser/tests/test_promise.py
+++ b/dom/bindings/parser/tests/test_promise.py
@@ -2,7 +2,6 @@ def WebIDLTest(parser, harness):
     threw = False
     try:
         parser.parse("""
-            interface _Promise {};
             interface A {
               legacycaller Promise<any> foo();
             };
@@ -18,7 +17,6 @@ def WebIDLTest(parser, harness):
     threw = False
     try:
         parser.parse("""
-            interface _Promise {};
             interface A {
               Promise<any> foo();
               long foo(long arg);
@@ -35,7 +33,6 @@ def WebIDLTest(parser, harness):
     threw = False
     try:
         parser.parse("""
-            interface _Promise {};
             interface A {
               long foo(long arg);
               Promise<any> foo();
@@ -50,7 +47,6 @@ def WebIDLTest(parser, harness):
 
     parser = parser.reset()
     parser.parse("""
-        interface _Promise {};
         interface A {
           Promise<any> foo();
           Promise<any> foo(long arg);