Also support mandatory top level options

Author: natebosch

pkgs/args/lib/src/parser.dart

@@ -122,7 +122,8 @@ class Parser {
     }
 
     // Check if mandatory and invoke existing callbacks.
-    final ignoreMandatoryOptions = _results.containsKey('help');
+    final ignoreMandatoryOptions =
+        _results.containsKey('help') || command?.name == 'help';
     _grammar.options.forEach((name, option) {
       var parsedOption = _results[name];
 

pkgs/args/test/command_runner_test.dart

@@ -799,6 +799,24 @@ Global options:
 Available commands:
   mandatory-option-command   A command with a mandatory option
 
+Run "test help <command>" for more information about a command.
+'''));
+  });
+
+  test('mandatory global options do not interfere with help command', () {
+    runner.argParser.addOption('mandatory', mandatory: true);
+    expect(() => runner.run(['help']), prints('''
+A test command runner.
+
+Usage: test <command> [arguments]
+
+Global options:
+-h, --help                     Print this usage information.
+    --mandatory (mandatory)    
+
+Available commands:
+  help   Display help information for test.
+
 Run "test help <command>" for more information about a command.
 '''));
   });