Prototypes should be regular objects.

This resolves #76

Merged remote-tracking branch 'janek/js_error_ordinary-object_1'

4 files changed, 58 insertions, 40 deletions

diff --git a/js/src/vm/ErrorObject.cpp b/js/src/vm/ErrorObject.cpp
index 47b61b57b..d8d29830b 100644
--- a/js/src/vm/ErrorObject.cpp
+++ b/js/src/vm/ErrorObject.cpp
@@ -164,29 +164,25 @@ js::ErrorObject::getOrCreateErrorReport(JSContext* cx)
 }
 
 static bool
-ErrorObject_checkAndUnwrapThis(JSContext* cx, CallArgs& args, const char* fnName,
-                               MutableHandle<ErrorObject*> error)
+FindErrorInstanceOrPrototype(JSContext* cx, HandleObject obj, MutableHandleObject result)
 {
-    const Value& thisValue = args.thisv();
-
-    if (!thisValue.isObject()) {
-        JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr, JSMSG_NOT_NONNULL_OBJECT,
-                                  InformalValueTypeName(thisValue));
-        return false;
-    }
-
-    // Walk up the prototype chain until we find the first ErrorObject that has
-    // the slots we need. This allows us to support the poor-man's subclassing
-    // of error: Object.create(Error.prototype).
-
-    RootedObject target(cx, CheckedUnwrap(&thisValue.toObject()));
+    // Walk up the prototype chain until we find an error object instance or
+    // prototype object. This allows code like:
+    //  Object.create(Error.prototype).stack
+    // or
+    //   function NYI() { }
+    //   NYI.prototype = new Error;
+    //   (new NYI).stack
+    // to continue returning stacks that are useless, but at least don't throw.
+
+    RootedObject target(cx, CheckedUnwrap(obj));
     if (!target) {
         JS_ReportErrorASCII(cx, "Permission denied to access object");
         return false;
     }
 
     RootedObject proto(cx);
-    while (!target->is<ErrorObject>()) {
+    while (!IsErrorProtoKey(StandardProtoKeyOrNull(target))) {
         if (!GetPrototype(cx, target, &proto))
             return false;
 
@@ -194,7 +190,7 @@ ErrorObject_checkAndUnwrapThis(JSContext* cx, CallArgs& args, const char* fnName
             // We walked the whole prototype chain and did not find an Error
             // object.
             JS_ReportErrorNumberASCII(cx, GetErrorMessage, nullptr, JSMSG_INCOMPATIBLE_PROTO,
-                                      js_Error_str, fnName, thisValue.toObject().getClass()->name);
+                                      js_Error_str, "(get stack)", obj->getClass()->name);
             return false;
         }
 
@@ -205,19 +201,40 @@ ErrorObject_checkAndUnwrapThis(JSContext* cx, CallArgs& args, const char* fnName
         }
     }
 
-    error.set(&target->as<ErrorObject>());
+    result.set(target);
     return true;
 }
 
+
+static MOZ_ALWAYS_INLINE bool
+IsObject(HandleValue v)
+{
+    return v.isObject();
+}
+
 /* static */ bool
 js::ErrorObject::getStack(JSContext* cx, unsigned argc, Value* vp)
 {
     CallArgs args = CallArgsFromVp(argc, vp);
-    Rooted<ErrorObject*> error(cx);
-    if (!ErrorObject_checkAndUnwrapThis(cx, args, "(get stack)", &error))
+    // We accept any object here, because of poor-man's subclassing of Error.
+    return CallNonGenericMethod<IsObject, getStack_impl>(cx, args);
+}
+
+/* static */ bool
+js::ErrorObject::getStack_impl(JSContext* cx, const CallArgs& args)
+{
+    RootedObject thisObj(cx, &args.thisv().toObject());
+
+    RootedObject obj(cx);
+    if (!FindErrorInstanceOrPrototype(cx, thisObj, &obj))
         return false;
 
-    RootedObject savedFrameObj(cx, error->stack());
+    if (!obj->is<ErrorObject>()) {
+        args.rval().setString(cx->runtime()->emptyString);
+        return true;
+    }
+
+    RootedObject savedFrameObj(cx, obj->as<ErrorObject>().stack());
     RootedString stackString(cx);
     if (!BuildStackString(cx, savedFrameObj, &stackString))
         return false;
@@ -245,12 +262,6 @@ js::ErrorObject::getStack(JSContext* cx, unsigned argc, Value* vp)
     return true;
 }
 
-static MOZ_ALWAYS_INLINE bool
-IsObject(HandleValue v)
-{
-    return v.isObject();
-}
-
 /* static */ bool
 js::ErrorObject::setStack(JSContext* cx, unsigned argc, Value* vp)
 {
@@ -262,9 +273,7 @@ js::ErrorObject::setStack(JSContext* cx, unsigned argc, Value* vp)
 /* static */ bool
 js::ErrorObject::setStack_impl(JSContext* cx, const CallArgs& args)
 {
-    const Value& thisValue = args.thisv();
-    MOZ_ASSERT(thisValue.isObject());
-    RootedObject thisObj(cx, &thisValue.toObject());
+    RootedObject thisObj(cx, &args.thisv().toObject());
 
     if (!args.requireAtLeast(cx, "(set stack)", 1))
         return false;
diff --git a/js/src/vm/ErrorObject.h b/js/src/vm/ErrorObject.h
index 32a691bb4..0c2d00610 100644
--- a/js/src/vm/ErrorObject.h
+++ b/js/src/vm/ErrorObject.h
@@ -38,9 +38,8 @@ class ErrorObject : public NativeObject
          ScopedJSFreePtr<JSErrorReport>* errorReport, HandleString fileName, HandleObject stack,
          uint32_t lineNumber, uint32_t columnNumber, HandleString message);
 
-    static const ClassSpec errorClassSpec_;
-    static const ClassSpec subErrorClassSpec_;
-    static const ClassSpec nonGlobalErrorClassSpec_;
+    static const ClassSpec classSpecs[JSEXN_ERROR_LIMIT];
+    static const Class protoClasses[JSEXN_ERROR_LIMIT];
 
   protected:
     static const uint32_t EXNTYPE_SLOT          = 0;
@@ -54,7 +53,7 @@ class ErrorObject : public NativeObject
     static const uint32_t RESERVED_SLOTS = MESSAGE_SLOT + 1;
 
   public:
-    static const Class classes[JSEXN_LIMIT];
+    static const Class classes[JSEXN_ERROR_LIMIT];
 
     static const Class * classForType(JSExnType type) {
         MOZ_ASSERT(type < JSEXN_WARN);
@@ -107,6 +106,7 @@ class ErrorObject : public NativeObject
 
     // Getter and setter for the Error.prototype.stack accessor.
     static bool getStack(JSContext* cx, unsigned argc, Value* vp);
+    static bool getStack_impl(JSContext* cx, const CallArgs& args);
     static bool setStack(JSContext* cx, unsigned argc, Value* vp);
     static bool setStack_impl(JSContext* cx, const CallArgs& args);
 };
diff --git a/js/src/vm/GlobalObject.h b/js/src/vm/GlobalObject.h
index 05984bc5f..3534ef2f6 100644
--- a/js/src/vm/GlobalObject.h
+++ b/js/src/vm/GlobalObject.h
@@ -427,6 +427,18 @@ class GlobalObject : public NativeObject
         return &global->getPrototype(key).toObject();
     }
 
+    static JSFunction*
+    getOrCreateErrorConstructor(JSContext* cx, Handle<GlobalObject*> global) {
+        if (!ensureConstructor(cx, global, JSProto_Error))
+            return nullptr;
+        return &global->getConstructor(JSProto_Error).toObject().as<JSFunction>();
+    }
+
+    static JSObject*
+    getOrCreateErrorPrototype(JSContext* cx, Handle<GlobalObject*> global) {
+        return getOrCreateCustomErrorPrototype(cx, global, JSEXN_ERR);
+    }
+
     static NativeObject* getOrCreateSetPrototype(JSContext* cx, Handle<GlobalObject*> global) {
         if (!ensureConstructor(cx, global, JSProto_Set))
             return nullptr;
@@ -1003,10 +1015,7 @@ GenericCreatePrototype(JSContext* cx, JSProtoKey key)
 inline JSProtoKey
 StandardProtoKeyOrNull(const JSObject* obj)
 {
-    JSProtoKey key = JSCLASS_CACHED_PROTO_KEY(obj->getClass());
-    if (key == JSProto_Error)
-        return GetExceptionProtoKey(obj->as<ErrorObject>().type());
-    return key;
+    return JSCLASS_CACHED_PROTO_KEY(obj->getClass());
 }
 
 JSObject*
diff --git a/js/src/vm/ObjectGroup.cpp b/js/src/vm/ObjectGroup.cpp
index 7be697fb6..d6a8fcaa4 100644
--- a/js/src/vm/ObjectGroup.cpp
+++ b/js/src/vm/ObjectGroup.cpp
@@ -6,6 +6,7 @@
 
 #include "vm/ObjectGroup.h"
 
+#include "jsexn.h"
 #include "jshashutil.h"
 #include "jsobj.h"
 
@@ -578,11 +579,10 @@ ObjectGroup::defaultNewGroup(ExclusiveContext* cx, const Class* clasp,
         AddTypePropertyId(cx, group, nullptr, NameToId(names.lastIndex), TypeSet::Int32Type());
     } else if (clasp == &StringObject::class_) {
         AddTypePropertyId(cx, group, nullptr, NameToId(names.length), TypeSet::Int32Type());
-    } else if (ErrorObject::isErrorClass((clasp))) {
+    } else if (ErrorObject::isErrorClass(clasp)) {
         AddTypePropertyId(cx, group, nullptr, NameToId(names.fileName), TypeSet::StringType());
         AddTypePropertyId(cx, group, nullptr, NameToId(names.lineNumber), TypeSet::Int32Type());
         AddTypePropertyId(cx, group, nullptr, NameToId(names.columnNumber), TypeSet::Int32Type());
-        AddTypePropertyId(cx, group, nullptr, NameToId(names.stack), TypeSet::StringType());
     }
 
     return group;