[isolate] Clean up MessageHandler::ReportMessage

- Use early return
- Add exception_string read-only root

Change-Id: Iba935a4a0308d21ced2693047fdf217b7f9e62f4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3097884Reviewed-by: Patrick Thier <pthier@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#76335}

src/execution/messages.cc

@@ -106,55 +106,55 @@ void MessageHandler::ReportMessage(Isolate* isolate, const MessageLocation* loc,
                                    Handle<JSMessageObject> message) {
   v8::Local<v8::Message> api_message_obj = v8::Utils::MessageToLocal(message);
 
-  if (api_message_obj->ErrorLevel() == v8::Isolate::kMessageError) {
-    // 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.
+  if (api_message_obj->ErrorLevel() != v8::Isolate::kMessageError) {
+    ReportMessageNoExceptions(isolate, loc, message, v8::Local<v8::Value>());
+    return;
+  }
 
-    // We pass the exception object into the message handler callback though.
-    Object exception_object = ReadOnlyRoots(isolate).undefined_value();
-    if (isolate->has_pending_exception()) {
-      exception_object = isolate->pending_exception();
-    }
-    Handle<Object> exception(exception_object, isolate);
+  // 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.
 
-    Isolate::ExceptionScope exception_scope(isolate);
-    isolate->clear_pending_exception();
-    isolate->set_external_caught_exception(false);
+  // We pass the exception object into the message handler callback though.
+  Object exception_object = ReadOnlyRoots(isolate).undefined_value();
+  if (isolate->has_pending_exception()) {
+    exception_object = isolate->pending_exception();
+  }
+  Handle<Object> exception(exception_object, isolate);
 
-    // 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);
+  Isolate::ExceptionScope exception_scope(isolate);
+  isolate->clear_pending_exception();
+  isolate->set_external_caught_exception(false);
 
-      MaybeHandle<Object> maybe_stringified;
-      Handle<Object> stringified;
-      // Make sure we don't leak uncaught internally generated Error objects.
-      if (argument->IsJSError()) {
-        maybe_stringified = Object::NoSideEffectsToString(isolate, argument);
-      } else {
-        v8::TryCatch catcher(reinterpret_cast<v8::Isolate*>(isolate));
-        catcher.SetVerbose(false);
-        catcher.SetCaptureMessage(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);
 
-        maybe_stringified = Object::ToString(isolate, argument);
-      }
+    MaybeHandle<Object> maybe_stringified;
+    Handle<Object> stringified;
+    // Make sure we don't leak uncaught internally generated Error objects.
+    if (argument->IsJSError()) {
+      maybe_stringified = Object::NoSideEffectsToString(isolate, argument);
+    } else {
+      v8::TryCatch catcher(reinterpret_cast<v8::Isolate*>(isolate));
+      catcher.SetVerbose(false);
+      catcher.SetCaptureMessage(false);
 
-      if (!maybe_stringified.ToHandle(&stringified)) {
-        DCHECK(isolate->has_pending_exception());
-        isolate->clear_pending_exception();
-        isolate->set_external_caught_exception(false);
-        stringified =
-            isolate->factory()->NewStringFromAsciiChecked("exception");
-      }
-      message->set_argument(*stringified);
+      maybe_stringified = Object::ToString(isolate, argument);
     }
 
-    v8::Local<v8::Value> api_exception_obj = v8::Utils::ToLocal(exception);
-    ReportMessageNoExceptions(isolate, loc, message, api_exception_obj);
-  } else {
-    ReportMessageNoExceptions(isolate, loc, message, v8::Local<v8::Value>());
+    if (!maybe_stringified.ToHandle(&stringified)) {
+      DCHECK(isolate->has_pending_exception());
+      isolate->clear_pending_exception();
+      isolate->set_external_caught_exception(false);
+      stringified = isolate->factory()->exception_string();
+    }
+    message->set_argument(*stringified);
   }
+
+  v8::Local<v8::Value> api_exception_obj = v8::Utils::ToLocal(exception);
+  ReportMessageNoExceptions(isolate, loc, message, api_exception_obj);
 }
 
 void MessageHandler::ReportMessageNoExceptions(

src/init/heap-symbols.h

@@ -198,13 +198,14 @@
   V(_, dot_string, ".")                                              \
   V(_, dot_switch_tag_string, ".switch_tag")                         \
   V(_, dotAll_string, "dotAll")                                      \
-  V(_, enumerable_string, "enumerable")                              \
-  V(_, element_string, "element")                                    \
   V(_, Error_string, "Error")                                        \
-  V(_, errors_string, "errors")                                      \
+  V(_, EvalError_string, "EvalError")                                \
+  V(_, element_string, "element")                                    \
+  V(_, enumerable_string, "enumerable")                              \
   V(_, error_to_string, "[object Error]")                            \
+  V(_, errors_string, "errors")                                      \
   V(_, eval_string, "eval")                                          \
-  V(_, EvalError_string, "EvalError")                                \
+  V(_, exception_string, "exception")                                \
   V(_, exec_string, "exec")                                          \
   V(_, false_string, "false")                                        \
   V(_, FinalizationRegistry_string, "FinalizationRegistry")          \