msvcrt: Support system(NULL).

dlls/msvcrt/process.c

@@ -1168,7 +1168,21 @@ int CDECL _wsystem(const MSVCRT_wchar_t* cmd)
   unsigned int len;
   static const MSVCRT_wchar_t flag[] = {' ','/','c',' ',0};
 
-  if (!(comspec = msvcrt_get_comspec())) return -1;
+  comspec = msvcrt_get_comspec();
+
+  if (cmd == NULL)
+  {
+    if (comspec == NULL)
+    {
+        *MSVCRT__errno() = MSVCRT_ENOENT;
+        return 0;
+    }
+    return 1;
+  }
+
+  if ( comspec == NULL)
+    return -1;
+
   len = strlenW(comspec) + strlenW(flag) + strlenW(cmd) + 1;
 
   if (!(fullcmd = HeapAlloc(GetProcessHeap(), 0, len * sizeof(MSVCRT_wchar_t))))
@@ -1195,6 +1209,9 @@ int CDECL MSVCRT_system(const char* cmd)
   int res = -1;
   MSVCRT_wchar_t *cmdW;
 
+  if (cmd == NULL)
+    return _wsystem(NULL);
+
   if ((cmdW = msvcrt_wstrdupa(cmd)))
   {
     res = _wsystem(cmdW);

dlls/msvcrt/tests/environ.c

@@ -42,6 +42,15 @@ static const char *a_very_long_env_string =
  "/usr/lib/mingw32/3.4.2/;"
  "/usr/lib/";
 
+static void test_system(void)
+{
+    int ret = system(NULL);
+    ok(ret == 1, "Expected system to return 1, got %d\n", ret);
+
+    ret = system("echo OK");
+    ok(ret == 0, "Expected system to return 0, got %d\n", ret);
+}
+
 START_TEST(environ)
 {
     ok( _putenv("cat=") == 0, "_putenv failed on deletion of nonexistent environment variable\n" );
@@ -54,4 +63,6 @@ START_TEST(environ)
     ok( _putenv(a_very_long_env_string) == 0, "_putenv failed for long environment string\n");
 
     ok( getenv("nonexistent") == NULL, "getenv should fail with nonexistent var name\n" );
+
+    test_system();
 }