Bug 911333 - Remove customTrace from bindings codegen. r=bz

dom/bindings/Bindings.conf

@@ -26,8 +26,6 @@
 #                interfaces.  Defaults to True otherwise.
 #   * workers - Indicates whether the descriptor is intended to be used for
 #               worker threads (defaults to false).
-#   * customTrace - The native class will use a custom trace hook (defaults to
-#                   true for workers, false otherwise).
 #   * customFinalize - The native class will use a custom finalize hook
 #                      (defaults to true for workers, false otherwise).
 #   * wantsQI - Indicates whether the interface should have a QueryInterface

dom/bindings/Codegen.py

@@ -18,7 +18,6 @@ AUTOGENERATED_WARNING_COMMENT = \
     "/* THIS FILE IS AUTOGENERATED - DO NOT EDIT */\n\n"
 ADDPROPERTY_HOOK_NAME = '_addProperty'
 FINALIZE_HOOK_NAME = '_finalize'
-TRACE_HOOK_NAME = '_trace'
 CONSTRUCT_HOOK_NAME = '_constructor'
 LEGACYCALLER_HOOK_NAME = '_legacycaller'
 HASINSTANCE_HOOK_NAME = '_hasInstance'
@@ -176,7 +175,10 @@ class CGDOMJSClass(CGThing):
     def declare(self):
         return ""
     def define(self):
-        traceHook = TRACE_HOOK_NAME if self.descriptor.customTrace else 'nullptr'
+        # Custom tracehooks are a footgun, so avoid supporting them. For instance,
+        # you have to be careful about barriers, and if you don't set a JSClass flag,
+        # then you'll end up permanently disabling incremental GC.
+        traceHook = 'nullptr'
         callHook = LEGACYCALLER_HOOK_NAME if self.descriptor.operations["LegacyCaller"] else 'nullptr'
         classFlags = "JSCLASS_IS_DOMJSCLASS | JSCLASS_HAS_RESERVED_SLOTS(3)"
         if self.descriptor.interface.getExtendedAttribute("NeedNewResolve"):
@@ -1068,20 +1070,6 @@ class CGClassFinalizeHook(CGAbstractClassHook):
     def generate_code(self):
         return CGIndenter(finalizeHook(self.descriptor, self.name, self.args[0].name)).define()
 
-class CGClassTraceHook(CGAbstractClassHook):
-    """
-    A hook to trace through our native object; used for GC and CC
-    """
-    def __init__(self, descriptor):
-        args = [Argument('JSTracer*', 'trc'), Argument('JSObject*', 'obj')]
-        CGAbstractClassHook.__init__(self, descriptor, TRACE_HOOK_NAME, 'void',
-                                     args)
-
-    def generate_code(self):
-        return """  if (self) {
-    self->%s(%s);
-  }""" % (self.name, self.args[0].name)
-
 class CGClassConstructor(CGAbstractStaticMethod):
     """
     JS-visible constructor for our objects
@@ -7975,10 +7963,6 @@ class CGDescriptor(CGThing):
             # wants a custom hook.
             cgThings.append(CGClassFinalizeHook(descriptor))
 
-            # Only generate a trace hook if the class wants a custom hook.
-            if (descriptor.customTrace):
-                cgThings.append(CGClassTraceHook(descriptor))
-
         properties = PropertyArrays(descriptor)
         cgThings.append(CGGeneric(define=str(properties)))
         cgThings.append(CGNativeProperties(descriptor, properties))

dom/bindings/Configuration.py

@@ -354,7 +354,6 @@ class Descriptor(DescriptorProvider):
                 raise TypeError("Descriptor for %s has unrecognized value (%s) "
                                 "for nativeOwnership" %
                                 (self.interface.identifier.name, self.nativeOwnership))
-        self.customTrace = desc.get('customTrace', self.workers)
         self.customFinalize = desc.get('customFinalize', self.workers)
         if desc.get('wantsQI', None) != None:
             self._wantsQI = desc.get('wantsQI', None)