Fix for issue-2837 (allow --print-flags without a script name).

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_debugger_api.h"
@@ skipping 172 matching lines @@
 }
 
 
 // Parse out the command line arguments. Returns -1 if the arguments
 // are incorrect, 0 otherwise.
 static int ParseArguments(int argc,
                           char** argv,
                           CommandLineOptions* vm_options,
                           char** executable_name,
                           char** script_name,
-                          CommandLineOptions* dart_options) {
+                          CommandLineOptions* dart_options,
+                          bool* print_flags_seen) {
   const char* kPrefix = "--";
   const intptr_t kPrefixLen = strlen(kPrefix);
 
   // Get the executable name.
   *executable_name = argv[0];
 
   // Start the rest after the executable name.
   int i = 1;
 
   // Parse out the vm options.
   while ((i < argc) && IsValidFlag(argv[i], kPrefix, kPrefixLen)) {
     if (ProcessMainOptions(argv[i])) {
       i++;
     } else {
+      const char* kPrintFlags1 = "--print-flags";
+      const char* kPrintFlags2 = "--print_flags";
+      if ((strncmp(argv[i], kPrintFlags1, strlen(kPrintFlags1)) == 0) ||
+          (strncmp(argv[i], kPrintFlags2, strlen(kPrintFlags2)) == 0)) {
+        *print_flags_seen = true;
+      }
       vm_options->AddArgument(argv[i]);
       i++;
     }
   }
   if (generate_pprof_symbols_filename != NULL) {
     Dart_InitPprofSupport();
   }
 
   if (flow_graph_file != NULL) {
     Dart_InitFlowGraphPrinting(&WriteToFlowGraphFile);
@@ skipping 459 matching lines @@
 }
 
 
 int main(int argc, char** argv) {
   char* executable_name;
   char* script_name;
   CommandLineOptions vm_options(argc);
   CommandLineOptions dart_options(argc);
   CommandLineOptions import_map(argc);
   import_map_options = &import_map;
+  bool print_flags_seen = false;
 
   // Perform platform specific initialization.
   if (!Platform::Initialize()) {
     fprintf(stderr, "Initialization failed\n");
   }
 
   // Parse command line arguments.
   if (ParseArguments(argc,
                      argv,
                      &vm_options,
                      &executable_name,
                      &script_name,
-                     &dart_options) < 0) {
-    PrintUsage();
-    return kErrorExitCode;
+                     &dart_options,
+                     &print_flags_seen) < 0) {
+    if (print_flags_seen) {
+      // Will set the VM flags, print them out and then we exit as no
+      // script was specified on the command line.
+      Dart_SetVMFlags(vm_options.count(), vm_options.arguments());
+      return 0;
+    } else {
+      PrintUsage();
+      return kErrorExitCode;
+    }
   }
 
   Dart_SetVMFlags(vm_options.count(), vm_options.arguments());
 
   // Initialize the Dart VM.
   Dart_Initialize(CreateIsolateAndSetup, NULL);
 
   original_working_directory = Directory::Current();
 
   // Call CreateIsolateAndSetup which creates an isolate and loads up
   // the specified application script.
   char* error = NULL;
   char* isolate_name = BuildIsolateName(script_name, "main");
   if (!CreateIsolateAndSetupHelper(script_name,
                                    "main",
                                    true,  // Canonicalize the script name.
                                    NULL,
                                    &error)) {
     fprintf(stderr, "%s\n", error);
     free(const_cast<char*>(original_working_directory));
     free(error);
     delete [] isolate_name;
-    return 255;  // Indicates we encountered an error.
+    return kErrorExitCode;  // Indicates we encountered an error.
   }
   delete [] isolate_name;
 
   Dart_Isolate isolate = Dart_CurrentIsolate();
   ASSERT(isolate != NULL);
   Dart_Handle result;
 
   Dart_EnterScope();
 
   if (has_compile_all) {
@@ skipping 47 matching lines @@
   DumpPprofSymbolInfo();
   // Shutdown the isolate.
   Dart_ShutdownIsolate();
   // Terminate process exit-code handler.
   Process::TerminateExitCodeHandler();
 
   free(const_cast<char*>(original_working_directory));
 
   return 0;
 }