1. Dynamic compute the main closure that needs to be run by the main isolate

runtime/bin/main.cc

 // Copyright (c) 2012, 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 <stdlib.h>
 #include <string.h>
 #include <stdio.h>
 
 #include "include/dart_api.h"
 #include "include/dart_tools_api.h"
@@ skipping 1469 matching lines @@
       result = Dart_ParseAll();
       CHECK_RESULT(result);
       Dart_ExitScope();
       // Shutdown the isolate.
       Dart_ShutdownIsolate();
       return false;
     }
 
     if (gen_snapshot_kind == kAppAOT) {
       Dart_QualifiedFunctionName standalone_entry_points[] = {
-          {"dart:_builtin", "::", "_getMainClosure"},
           {"dart:_builtin", "::", "_getPrintClosure"},
           {"dart:_builtin", "::", "_getUriBaseClosure"},
           {"dart:_builtin", "::", "_libraryFilePath"},
           {"dart:_builtin", "::", "_resolveInWorkingDirectory"},
           {"dart:_builtin", "::", "_setPackageRoot"},
           {"dart:_builtin", "::", "_setPackagesMap"},
           {"dart:_builtin", "::", "_setWorkingDirectory"},
           {"dart:async", "::", "_setScheduleImmediateClosure"},
           {"dart:io", "::", "_getWatchSignalInternal"},
           {"dart:io", "::", "_makeDatagram"},
@@ skipping 63 matching lines @@
       }
 
       if (load_compilation_trace_filename != NULL) {
         uint8_t* buffer = NULL;
         intptr_t size = 0;
         ReadFile(load_compilation_trace_filename, &buffer, &size);
         result = Dart_LoadCompilationTrace(buffer, size);
         CHECK_RESULT(result);
       }
 
-      // The helper function _getMainClosure creates a closure for the main
-      // entry point which is either explicitly or implictly exported from the
-      // root library.
+      // Create a closure for the main entry point which is in the exported
+      // namespace of the root library or invoke a getter of the same name
+      // in the exported namespace and return the resulting closure.
       Dart_Handle main_closure =
-          Dart_Invoke(isolate_data->builtin_lib(),
-                      Dart_NewStringFromCString("_getMainClosure"), 0, NULL);
+          Dart_GetClosure(root_lib, Dart_NewStringFromCString("main"));
       CHECK_RESULT(main_closure);
+      if (!Dart_IsClosure(main_closure)) {
+        ErrorExit(kErrorExitCode,
+                  "Unable to find 'main' in root library '%s'\n", script_name);
+      }
 
       // Call _startIsolate in the isolate library to enable dispatching the
       // initial startup message.
       const intptr_t kNumIsolateArgs = 2;
       Dart_Handle isolate_args[kNumIsolateArgs];
       isolate_args[0] = main_closure;                        // entryPoint
       isolate_args[1] = CreateRuntimeOptions(dart_options);  // args
 
       Dart_Handle isolate_lib =
           Dart_LookupLibrary(Dart_NewStringFromCString("dart:isolate"));
@@ skipping 324 matching lines @@
   Platform::Exit(Process::GlobalExitCode());
 }
 
 }  // namespace bin
 }  // namespace dart
 
 int main(int argc, char** argv) {
   dart::bin::main(argc, argv);
   UNREACHABLE();
 }