Very simple version of Isolates.

runtime/bin/main.cc

Index: runtime/bin/main.cc
diff --git a/runtime/bin/main.cc b/runtime/bin/main.cc
index 76c00626bbf200657ca9a997ac7ee7affcbb0911..e814ca3113ab2ef9943231d60dce0afebe5bff5d 100644
--- a/runtime/bin/main.cc
+++ b/runtime/bin/main.cc
@@ -863,16 +863,32 @@ int main(int argc, char** argv) {
       }
     } else {
       // Lookup and invoke the top level main function.
-      Dart_Handle main_args[1];
+      // The top-level function may accept up to two arguments:
+      //   main(List<String> args, var message).
+      // However most commonly it either accepts one (the args list) or
+      // none.
+      // If the message is optional, main(args, [message]), it is invoked with
+      // one argument only.
+      Dart_Handle main_args[2];
       main_args[0] = CreateRuntimeOptions(&dart_options);
+      main_args[1] = Dart_Null();
+      // First try with 1 argument.

[Lasse Reichstein Nielsen, 2013/10/25 09:42:49]

Could we inspect the function to see its signature, instead of trying to invoke
and failing? Or is trying to invoke efficient enough that it's not an overhead
(with the TODO below fixed)?

[floitsch, 2013/10/25 13:11:01]

It will be fixed. The TODO below is from Ivan. This is just a temporary
solution.

       result = Dart_Invoke(library, DartUtils::NewString("main"), 1, main_args);
       // TODO(iposva): Return a special error type for mismatched argument
       // counts from Dart_Invoke to avoid the string comparison.
       const char* expected_error = "Dart_Invoke: wrong argument count for "
-          "function 'main': 1 passed, 0 expected.";
+          "function 'main': ";
+      intptr_t length = strlen(expected_error);
       if (Dart_IsError(result) &&
-          strcmp(expected_error, Dart_GetError(result)) == 0) {
-        result = Dart_Invoke(library, DartUtils::NewString("main"), 0, NULL);
+          strncmp(expected_error, Dart_GetError(result), length) == 0) {
+        // Try with two arguments.

[Lasse Reichstein Nielsen, 2013/10/25 09:42:49]

Say why we try two before zero.

We really want to pass the first argument (which we have), and don't care about
passing the second (which we don't have anyway).

[floitsch, 2013/10/25 13:11:01]

See comment above.

+        result =
+            Dart_Invoke(library, DartUtils::NewString("main"), 2, main_args);
+        if (Dart_IsError(result) &&
+            strncmp(expected_error, Dart_GetError(result), length) == 0) {
+          // Finally try with 0 arguments.
+          result = Dart_Invoke(library, DartUtils::NewString("main"), 0, NULL);
+        }
       }
       if (Dart_IsError(result)) {
         return DartErrorExit(result);