Make Error.prototype.toString spec compliant; and fix various side-effect-free error printing metho…

src/js/messages.js

Index: src/js/messages.js
diff --git a/src/js/messages.js b/src/js/messages.js
index dc845ea97adc855fa7d0847374dad1af99e7551a..d0305412b74896a7971e4e435032b5f9a8ee3a05 100644
--- a/src/js/messages.js
+++ b/src/js/messages.js
@@ -23,6 +23,7 @@ var callSitePositionSymbol =
     utils.ImportNow("call_site_position_symbol");
 var callSiteStrictSymbol =
     utils.ImportNow("call_site_strict_symbol");
+var FLAG_harmony_tostring;
 var Float32x4ToString;
 var formattedStackTraceSymbol =
     utils.ImportNow("formatted_stack_trace_symbol");
@@ -41,6 +42,7 @@ var StringCharAt;
 var StringIndexOf;
 var StringSubstring;
 var SymbolToString;
+var toStringTagSymbol = utils.ImportNow("to_string_tag_symbol");
 var Uint16x8ToString;
 var Uint32x4ToString;
 var Uint8x16ToString;
@@ -66,6 +68,10 @@ utils.Import(function(from) {
   Uint8x16ToString = from.Uint8x16ToString;
 });
 
+utils.ImportFromExperimental(function(from) {
+  FLAG_harmony_tostring = from.FLAG_harmony_tostring;
+});
+
 // -------------------------------------------------------------------
 
 var GlobalError;
@@ -80,11 +86,35 @@ var GlobalEvalError;
 function NoSideEffectsObjectToString() {
   if (IS_UNDEFINED(this)) return "[object Undefined]";
   if (IS_NULL(this)) return "[object Null]";
-  return "[object " + %_ClassOf(TO_OBJECT(this)) + "]";
+  var O = TO_OBJECT(this);
+  var builtinTag = %_ClassOf(O);
+  var tag;
+  if (FLAG_harmony_tostring) {
+    tag = %GetDataProperty(O, toStringTagSymbol);
+    if (!IS_STRING(tag)) {
+      tag = builtinTag;
+    }
+  } else {
+    tag = builtinTag;
+  }
+  return `[object ${tag}]`;
+}
+
+function IsErrorObject(obj) {
+  return HAS_PRIVATE(obj, stackTraceSymbol);
 }
 
+function NoSideEffectsErrorToString() {
+  var name = %GetDataProperty(this, "name");
+  var message = %GetDataProperty(this, "message");
+  name = IS_UNDEFINED(name) ? "Error" : NoSideEffectsToString(name);
+  message = IS_UNDEFINED(message) ? "" : NoSideEffectsToString(message);
+  if (name == "") return message;
+  if (message == "") return name;
+  return `${name}: ${message}`;
+}
 
-function NoSideEffectToString(obj) {
+function NoSideEffectsToString(obj) {
   if (IS_STRING(obj)) return obj;
   if (IS_NUMBER(obj)) return %_NumberToString(obj);
   if (IS_BOOLEAN(obj)) return obj ? 'true' : 'false';
@@ -113,69 +143,26 @@ function NoSideEffectToString(obj) {
       case 'bool8x16':  return %_Call(Bool8x16ToString, obj);
     }
   }
-  if (IS_OBJECT(obj)
-      && %GetDataProperty(obj, "toString") === ObjectToString) {
-    var constructor = %GetDataProperty(obj, "constructor");
-    if (typeof constructor == "function") {
-      var constructorName = constructor.name;
-      if (IS_STRING(constructorName) && constructorName !== "") {
-        return "#<" + constructorName + ">";
-      }
-    }
-  }
-  if (CanBeSafelyTreatedAsAnErrorObject(obj)) {
-    return %_Call(ErrorToString, obj);
-  }
-
-  return %_Call(NoSideEffectsObjectToString, obj);
-}
-
-// To determine whether we can safely stringify an object using ErrorToString
-// without the risk of side-effects, we need to check whether the object is
-// either an instance of a native error type (via '%_ClassOf'), or has Error
-// in its prototype chain and hasn't overwritten 'toString' with something
-// strange and unusual.
-function CanBeSafelyTreatedAsAnErrorObject(obj) {
-  switch (%_ClassOf(obj)) {
-    case 'Error':
-    case 'EvalError':
-    case 'RangeError':
-    case 'ReferenceError':
-    case 'SyntaxError':
-    case 'TypeError':
-    case 'URIError':
-      return true;
-  }
-
-  var objToString = %GetDataProperty(obj, "toString");
-  return obj instanceof GlobalError && objToString === ErrorToString;
-}
-
-
-// When formatting internally created error messages, do not
-// invoke overwritten error toString methods but explicitly use
-// the error to string method. This is to avoid leaking error
-// objects between script tags in a browser setting.
-function ToStringCheckErrorObject(obj) {
-  if (CanBeSafelyTreatedAsAnErrorObject(obj)) {
-    return %_Call(ErrorToString, obj);
-  } else {
-    return TO_STRING(obj);
-  }
-}
 
+  if (IS_SPEC_OBJECT(obj)) {
+    // When internally formatting error objects, use a side-effects-free version
+    // of Error.prototype.toString independent of the actually installed
+    // toString method.
+    if (IsErrorObject(obj) ||
+        %GetDataProperty(obj, "toString") === ErrorToString) {
+      return %_Call(NoSideEffectsErrorToString, obj);
+    }
 
-function ToDetailString(obj) {
-  if (obj != null && IS_OBJECT(obj) && obj.toString === ObjectToString) {
-    var constructor = obj.constructor;
-    if (typeof constructor == "function") {
-      var constructorName = constructor.name;
-      if (IS_STRING(constructorName) && constructorName !== "") {
-        return "#<" + constructorName + ">";
+    if (%GetDataProperty(obj, "toString") === ObjectToString) {
+      var constructor = %GetDataProperty(obj, "constructor");
+      if (IS_FUNCTION(constructor)) {
+        var constructor_name = %FunctionGetName(constructor);
+        if (constructor_name != "") return `#<${constructor_name}>`;
       }
     }
   }
-  return ToStringCheckErrorObject(obj);
+
+  return %_Call(NoSideEffectsObjectToString, obj);
 }
 
 
@@ -200,9 +187,9 @@ function MakeGenericError(constructor, type, arg0, arg1, arg2) {
 
 // Helper functions; called from the runtime system.
 function FormatMessage(type, arg0, arg1, arg2) {
-  var arg0 = NoSideEffectToString(arg0);
-  var arg1 = NoSideEffectToString(arg1);
-  var arg2 = NoSideEffectToString(arg2);
+  var arg0 = NoSideEffectsToString(arg0);
+  var arg1 = NoSideEffectsToString(arg1);
+  var arg2 = NoSideEffectsToString(arg2);
   try {
     return %FormatMessageString(type, arg0, arg1, arg2);
   } catch (e) {
@@ -849,20 +836,13 @@ function FormatStackTrace(obj, raw_stack) {
 
 function GetTypeName(receiver, requireConstructor) {
   if (IS_NULL_OR_UNDEFINED(receiver)) return null;
-  if (%_IsJSProxy(receiver)) {
-    return "Proxy";
-  };
-  var constructor = receiver.constructor;
-  if (!constructor) {
-    return requireConstructor ? null :
-        %_Call(NoSideEffectsObjectToString, receiver);
-  }
-  var constructorName = constructor.name;
-  if (!constructorName) {
-    return requireConstructor ? null :
-        %_Call(NoSideEffectsObjectToString, receiver);
+  if (%_IsJSProxy(receiver)) return "Proxy";
+
+  var constructor = %GetDataProperty(TO_OBJECT(receiver), "constructor");
+  if (!IS_FUNCTION(constructor)) {
+    return requireConstructor ? null : %_Call(NoSideEffectsToString, receiver);
   }
-  return constructorName;
+  return %FunctionGetName(constructor);
 }
 
 
@@ -896,7 +876,7 @@ var StackTraceGetter = function() {
 // If the receiver equals the holder, set the formatted stack trace that the
 // getter returns.
 var StackTraceSetter = function(v) {
-  if (HAS_PRIVATE(this, stackTraceSymbol)) {
+  if (IsErrorObject(this)) {
     SET_PRIVATE(this, stackTraceSymbol, UNDEFINED);
     SET_PRIVATE(this, formattedStackTraceSymbol, v);
   }
@@ -956,7 +936,15 @@ function ErrorToString() {
     throw MakeTypeError(kCalledOnNonObject, "Error.prototype.toString");
   }
 
-  return %ErrorToStringRT(this);
+  var name = this.name;
+  name = IS_UNDEFINED(name) ? "Error" : TO_STRING(name);
+
+  var message = this.message;
+  message = IS_UNDEFINED(message) ? "" : TO_STRING(message);
+
+  if (name == "") return message;
+  if (message == "") return name;
+  return `${name}: ${message}`
 }
 
 function MakeError(type, arg0, arg1, arg2) {
@@ -1004,9 +992,8 @@ GlobalError.captureStackTrace = captureStackTrace;
   "message_get_column_number", GetColumnNumber,
   "message_get_line_number", GetLineNumber,
   "message_get_source_line", GetSourceLine,
-  "no_side_effect_to_string_fun", NoSideEffectToString,
+  "no_side_effects_to_string_fun", NoSideEffectsToString,
   "stack_overflow_boilerplate", StackOverflowBoilerplate,
-  "to_detail_string_fun", ToDetailString,
 ]);
 
 utils.Export(function(to) {