Do not eagerly convert exception to string when creating a message object

src/messages.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/v8.h"
 
 #include "src/api.h"
 #include "src/execution.h"
 #include "src/heap/spaces-inl.h"
 #include "src/messages.h"
@@ skipping 41 matching lines @@
       ? Handle<Object>::cast(factory->undefined_value())
       : Handle<Object>::cast(stack_frames);
 
   Handle<JSMessageObject> message_obj = factory->NewJSMessageObject(
       message, argument, start, end, script_handle, stack_frames_handle);
 
   return message_obj;
 }
 
 
-void MessageHandler::ReportMessage(Isolate* isolate,
-                                   MessageLocation* loc,
-                                   Handle<Object> message) {
+void MessageHandler::ReportMessage(Isolate* isolate, MessageLocation* loc,
+                                   Handle<JSMessageObject> message) {
   // We are calling into embedder's code which can throw exceptions.
   // Thus we need to save current exception state, reset it to the clean one
   // and ignore scheduled exceptions callbacks can throw.
 
   // We pass the exception object into the message handler callback though.
   Object* exception_object = isolate->heap()->undefined_value();
   if (isolate->has_pending_exception()) {
     exception_object = isolate->pending_exception();
   }
-  Handle<Object> exception_handle(exception_object, isolate);
+  Handle<Object> exception(exception_object, isolate);
 
   Isolate::ExceptionScope exception_scope(isolate);
   isolate->clear_pending_exception();
   isolate->set_external_caught_exception(false);
 
+  // Turn the exception on the message into a string if it is an object.
+  if (message->argument()->IsJSObject()) {
+    HandleScope scope(isolate);
+    Handle<Object> argument(message->argument(), isolate);
+    Handle<Object> args[] = {argument};
+    MaybeHandle<Object> maybe_stringified = Execution::TryCall(
+        isolate->to_detail_string_fun(), isolate->js_builtins_object(),
+        arraysize(args), args);
+    Handle<Object> stringified;
+    if (!maybe_stringified.ToHandle(&stringified)) {
+      stringified = isolate->factory()->NewStringFromAsciiChecked("exception");
+    }
+    message->set_argument(*stringified);
+  }
+
   v8::Local<v8::Message> api_message_obj = v8::Utils::MessageToLocal(message);
-  v8::Local<v8::Value> api_exception_obj = v8::Utils::ToLocal(exception_handle);
+  v8::Local<v8::Value> api_exception_obj = v8::Utils::ToLocal(exception);
 
   v8::NeanderArray global_listeners(isolate->factory()->message_listeners());
   int global_length = global_listeners.length();
   if (global_length == 0) {
     DefaultMessageReport(isolate, loc, message);
     if (isolate->has_scheduled_exception()) {
       isolate->clear_scheduled_exception();
     }
   } else {
     for (int i = 0; i < global_length; i++) {
@@ skipping 181 matching lines @@
       JSReceiver::GetDataProperty(Handle<JSObject>::cast(receiver_),
                                   isolate->factory()->constructor_string());
   return constructor.is_identical_to(fun_);
 }
 
 
 Handle<String> MessageTemplate::FormatMessage(Isolate* isolate,
                                               int template_index,
                                               Handle<Object> arg) {
   Factory* factory = isolate->factory();
-  Handle<String> fmt_str = factory->InternalizeOneByteString(
-      STATIC_CHAR_VECTOR("$noSideEffectToString"));
-  Handle<JSFunction> fun = Handle<JSFunction>::cast(
-      Object::GetProperty(isolate->js_builtins_object(), fmt_str)
-          .ToHandleChecked());
+  Handle<String> result_string;
+  if (arg->IsString()) {
+    result_string = Handle<String>::cast(arg);
+  } else {
+    Handle<String> fmt_str = factory->InternalizeOneByteString(
+        STATIC_CHAR_VECTOR("$noSideEffectToString"));
+    Handle<JSFunction> fun = Handle<JSFunction>::cast(
+        Object::GetProperty(isolate->js_builtins_object(), fmt_str)
+            .ToHandleChecked());
 
-  MaybeHandle<Object> maybe_result =
-      Execution::TryCall(fun, isolate->js_builtins_object(), 1, &arg);
-  Handle<Object> result;
-  if (!maybe_result.ToHandle(&result) || !result->IsString()) {
-    return factory->InternalizeOneByteString(STATIC_CHAR_VECTOR("<error>"));
+    MaybeHandle<Object> maybe_result =
+        Execution::TryCall(fun, isolate->js_builtins_object(), 1, &arg);
+    Handle<Object> result;
+    if (!maybe_result.ToHandle(&result) || !result->IsString()) {
+      return factory->InternalizeOneByteString(STATIC_CHAR_VECTOR("<error>"));
+    }
+    result_string = Handle<String>::cast(result);
   }
   MaybeHandle<String> maybe_result_string = MessageTemplate::FormatMessage(
-      template_index, Handle<String>::cast(result), factory->empty_string(),
+      template_index, result_string, factory->empty_string(),
       factory->empty_string());
-  Handle<String> result_string;
   if (!maybe_result_string.ToHandle(&result_string)) {
     return factory->InternalizeOneByteString(STATIC_CHAR_VECTOR("<error>"));
   }
   // A string that has been obtained from JS code in this way is
   // likely to be a complicated ConsString of some sort.  We flatten it
   // here to improve the efficiency of converting it to a C string and
   // other operations that are likely to take place (see GetLocalizedMessage
   // for example).
   return String::Flatten(result_string);
 }
@@ skipping 34 matching lines @@
         builder.AppendString(args[i++]);
       }
     } else {
       builder.AppendCharacter(*c);
     }
   }
 
   return builder.Finish();
 }
 } }  // namespace v8::internal