From 15194f2f0709810e0add44ab6c39ad49ae766647 Mon Sep 17 00:00:00 2001
From: Boris Zbarsky <bzbarsky@mit.edu>
Date: Fri, 15 Sep 2017 23:45:06 -0400
Subject: [PATCH] Bug 1400275.  Ensure we create reflectors for JS-implemented
 webidl interfaces with the right prototype when those interfaces are
 subclassed.  r=qdot

MozReview-Commit-ID: 5yYD92NVVFQ
---
 dom/bindings/Codegen.py                       | 20 +++++++++---
 dom/bindings/test/mochitest.ini               |  1 +
 .../test/test_jsimplemented_subclassing.html  | 31 +++++++++++++++++++
 3 files changed, 47 insertions(+), 5 deletions(-)
 create mode 100644 dom/bindings/test/test_jsimplemented_subclassing.html

diff --git a/dom/bindings/Codegen.py b/dom/bindings/Codegen.py
index 90badb235b30..5742c2a24dbd 100644
--- a/dom/bindings/Codegen.py
+++ b/dom/bindings/Codegen.py
@@ -7734,6 +7734,10 @@ class CGPerSignatureCall(CGThing):
             needsUnwrap = True
             needsUnwrappedVar = False
             unwrappedVar = "obj"
+            if descriptor.interface.isJSImplemented():
+                # We need the desired proto in our constructor, because the
+                # constructor will actually construct our reflector.
+                argsPost.append("desiredProto")
         elif descriptor.interface.isJSImplemented():
             if not idlNode.isStatic():
                 needsUnwrap = True
@@ -15335,8 +15339,10 @@ class CGJSImplMethod(CGJSImplMember):
     def getArgs(self, returnType, argList):
         if self.isConstructor:
             # Skip the JSCompartment bits for constructors; it's handled
-            # manually in getImpl.
-            return CGNativeMember.getArgs(self, returnType, argList)
+            # manually in getImpl.  But we do need our aGivenProto argument.  We
+            # allow it to be omitted if the default proto is desired.
+            return (CGNativeMember.getArgs(self, returnType, argList) +
+                    [Argument("JS::Handle<JSObject*>", "aGivenProto", "nullptr")])
         return CGJSImplMember.getArgs(self, returnType, argList)
 
     def getImpl(self):
@@ -15349,10 +15355,14 @@ class CGJSImplMethod(CGJSImplMember):
             raise TypeError("Named constructors are not supported for JS implemented WebIDL. See bug 851287.")
         if len(self.signature[1]) != 0:
             # The first two arguments to the constructor implementation are not
-            # arguments to the WebIDL constructor, so don't pass them to __Init()
+            # arguments to the WebIDL constructor, so don't pass them to
+            # __Init().  The last argument is the prototype we're supposed to
+            # use, and shouldn't get passed to __Init() either.
             assert args[0].argType == 'const GlobalObject&'
             assert args[1].argType == 'JSContext*'
-            constructorArgs = [arg.name for arg in args[2:]]
+            assert args[-1].argType == 'JS::Handle<JSObject*>'
+            assert args[-1].name == 'aGivenProto'
+            constructorArgs = [arg.name for arg in args[2:-1]]
             constructorArgs.append("js::GetObjectCompartment(scopeObj)")
             initCall = fill(
                 """
@@ -15360,7 +15370,7 @@ class CGJSImplMethod(CGJSImplMember):
                 JS::Rooted<JSObject*> scopeObj(cx, globalHolder->GetGlobalJSObject());
                 MOZ_ASSERT(js::IsObjectInContextCompartment(scopeObj, cx));
                 JS::Rooted<JS::Value> wrappedVal(cx);
-                if (!GetOrCreateDOMReflector(cx, impl, &wrappedVal)) {
+                if (!GetOrCreateDOMReflector(cx, impl, &wrappedVal, aGivenProto)) {
                   //XXX Assertion disabled for now, see bug 991271.
                   MOZ_ASSERT(true || JS_IsExceptionPending(cx));
                   aRv.Throw(NS_ERROR_UNEXPECTED);
diff --git a/dom/bindings/test/mochitest.ini b/dom/bindings/test/mochitest.ini
index 621bac5c70f6..6b082bbef018 100644
--- a/dom/bindings/test/mochitest.ini
+++ b/dom/bindings/test/mochitest.ini
@@ -81,3 +81,4 @@ skip-if = debug == false
 skip-if = os == "android"
 [test_stringBindings.html]
 skip-if = debug == false
+[test_jsimplemented_subclassing.html]
diff --git a/dom/bindings/test/test_jsimplemented_subclassing.html b/dom/bindings/test/test_jsimplemented_subclassing.html
new file mode 100644
index 000000000000..3a5089c3942b
--- /dev/null
+++ b/dom/bindings/test/test_jsimplemented_subclassing.html
@@ -0,0 +1,31 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1400275
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1400275</title>
+  <script type="application/javascript" src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+
+  /** Test for Bug 1400275 **/
+    class Foo extends RTCPeerConnection {
+    }
+
+    var obj = new Foo();
+    is(Object.getPrototypeOf(obj), Foo.prototype,
+       "Should have the right prototype");
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1400275">Mozilla Bug 1400275</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>