[wasm] [asmjs] Route asm.js warnings to the dev console.

src/d8.cc

 // Copyright 2012 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 <errno.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/stat.h>
 
 #include <algorithm>
@@ skipping 1561 matching lines @@
   Local<ObjectTemplate> os_templ = ObjectTemplate::New(isolate);
   AddOSMethods(isolate, os_templ);
   global_template->Set(
       String::NewFromUtf8(isolate, "os", NewStringType::kNormal)
           .ToLocalChecked(),
       os_templ);
 
   return global_template;
 }
 
-static void EmptyMessageCallback(Local<Message> message, Local<Value> error) {
-  // Nothing to be done here, exceptions thrown up to the shell will be reported
+static void PrintNonErrorsMessageCallback(Local<Message> message,
+                                          Local<Value> error) {
+  // Nothing to do here for errors, exceptions thrown up to the shell will be
+  // reported
   // separately by {Shell::ReportException} after they are caught.
+  // Do print other kinds of messages.
+  switch (message->ErrorLevel()) {
+    case v8::Isolate::kMessageWarning:
+    case v8::Isolate::kMessageLog:
+    case v8::Isolate::kMessageInfo:
+    case v8::Isolate::kMessageDebug: {
+      break;
+    }
+
+    case v8::Isolate::kMessageError: {
+      // Ignore errors, printed elsewhere.
+      return;
+    }
+
+    default: {
+      UNREACHABLE();
+      break;
+    }
+  }
+  // Converts a V8 value to a C string.
+  auto ToCString = [](const v8::String::Utf8Value& value) {
+    return *value ? *value : "<string conversion failed>";
+  };
+  Isolate* isolate = Isolate::GetCurrent();
+  v8::String::Utf8Value msg(message->Get());
+  const char* msg_string = ToCString(msg);
+  // Print (filename):(line number): (message).
+  v8::String::Utf8Value filename(message->GetScriptOrigin().ResourceName());
+  const char* filename_string = ToCString(filename);
+  Maybe<int> maybeline = message->GetLineNumber(isolate->GetCurrentContext());
+  int linenum = maybeline.IsJust() ? maybeline.FromJust() : -1;
+  printf("%s:%i: %s\n", filename_string, linenum, msg_string);
 }
 
 void Shell::Initialize(Isolate* isolate) {
   // Set up counters
   if (i::StrLength(i::FLAG_map_counters) != 0)
     MapCounters(isolate, i::FLAG_map_counters);
   // Disable default message reporting.
-  isolate->AddMessageListener(EmptyMessageCallback);
+  isolate->AddMessageListenerWithErrorLevel(
+      PrintNonErrorsMessageCallback,
+      v8::Isolate::kMessageError | v8::Isolate::kMessageWarning |
+          v8::Isolate::kMessageInfo | v8::Isolate::kMessageDebug |
+          v8::Isolate::kMessageLog);
 }
 
 
 Local<Context> Shell::CreateEvaluationContext(Isolate* isolate) {
   // This needs to be a critical section since this is not thread-safe
   base::LockGuard<base::Mutex> lock_guard(context_mutex_.Pointer());
   // Initialize the global objects
   Local<ObjectTemplate> global_template = CreateGlobalTemplate(isolate);
   EscapableHandleScope handle_scope(isolate);
   Local<Context> context = Context::New(isolate, NULL, global_template);
@@ skipping 1417 matching lines @@
 }
 
 }  // namespace v8
 
 
 #ifndef GOOGLE3
 int main(int argc, char* argv[]) {
   return v8::Shell::Main(argc, argv);
 }
 #endif