Get the OS error message for process exceptions on Windows

bin/process_win.cc

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include <process.h>
 
 #include "bin/builtin.h"
 #include "bin/globals.h"
 #include "bin/process.h"
 #include "bin/eventhandler.h"
@@ skipping 162 matching lines @@
                               HANDLE handles2[2],
                               HANDLE handles3[2],
                               HANDLE handles4[2]) {
   CloseProcessPipe(handles1);
   CloseProcessPipe(handles2);
   CloseProcessPipe(handles3);
   CloseProcessPipe(handles4);
 }
 
 static int SetOsErrorMessage(char* os_error_message,
-                              int os_error_message_len) {
+                             int os_error_message_len) {
   int error_code = GetLastError();
-  // TODO(sgjesse): Use FormatMessage to get the error message.
-  char message[80];
-  snprintf(os_error_message, os_error_message_len, "OS Error %d", error_code);
+  DWORD message_size =
+      FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
+                    NULL,
+                    error_code,
+                    MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
+                    os_error_message,
+                    os_error_message_len,
+                    NULL);
+  if (message_size == 0) {
+    if (GetLastError() != ERROR_INSUFFICIENT_BUFFER) {
+      fprintf(stderr, "FormatMessage failed %d\n", GetLastError());
+    }
+    snprintf(os_error_message, os_error_message_len, "OS Error %d", error_code);
+  }
+  os_error_message[os_error_message_len - 1] = '\0';
   return error_code;
 }
 
 
 static unsigned int __stdcall TerminationWaitThread(void* args) {
   ProcessInfo* process = reinterpret_cast<ProcessInfo*>(args);
   WaitForSingleObject(process->process_handle(), INFINITE);
   DWORD exit_code;
   BOOL ok = GetExitCodeProcess(process->process_handle(), &exit_code);
   if (!ok) {
@@ skipping 189 matching lines @@
       return false;
     }
   }
   return true;
 }
 
 
 void Process::Exit(intptr_t id) {
   RemoveProcess(id);
 }