fix: ArgResults.operator[] should throw Exception not Error

ArgResults.operator[] and ArgResults.option() would throw
ArgumentError instead of Exception when the user would fail to
pass all expected arguments.

Errors are only supposed to be thrown on programmer error so
changed to throw ArgParserException instead.

This is a breaking change!

Author: eseidel

pkgs/args/lib/src/arg_results.dart

@@ -5,6 +5,7 @@
 import 'dart:collection';
 
 import 'arg_parser.dart';
+import 'arg_parser_exception.dart';
 
 /// Creates a new [ArgResults].
 ///
@@ -71,7 +72,7 @@ class ArgResults {
 
     final option = _parser.options[name]!;
     if (option.mandatory && !_parsed.containsKey(name)) {
-      throw ArgumentError('Option $name is mandatory.');
+      throw ArgParserException('Option $name is mandatory.');
     }
 
     return option.valueOrDefault(_parsed[name]);
@@ -103,7 +104,7 @@ class ArgResults {
       throw ArgumentError('"$name" is a multi-option.');
     }
     if (option.mandatory && !_parsed.containsKey(name)) {
-      throw ArgumentError('Option $name is mandatory.');
+      throw ArgParserException('Option $name is mandatory.');
     }
     return option.valueOrDefault(_parsed[name]) as String?;
   }

pkgs/args/test/command_runner_test.dart

@@ -2,6 +2,7 @@
 // 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.
 
+import 'package:args/args.dart';
 import 'package:args/command_runner.dart';
 import 'package:test/test.dart';
 
@@ -736,7 +737,7 @@ Run "test help" to see global options.'''));
     runner.addCommand(subcommand);
     expect(
         () => runner.run([subcommand.name]),
-        throwsA(isA<ArgumentError>().having((e) => e.message, 'message',
+        throwsA(isA<ArgParserException>().having((e) => e.message, 'message',
             contains('Option mandatory-option is mandatory'))));
     expect(await runner.run([subcommand.name, '--mandatory-option', 'foo']),
         'foo');

pkgs/args/test/parse_test.dart

@@ -595,7 +595,10 @@ void main() {
           var parser = ArgParser();
           parser.addOption('username', mandatory: true);
           var results = parser.parse([]);
-          expect(() => results['username'], throwsA(isA<ArgumentError>()));
+          expect(
+              () => results['username'],
+              throwsA(isA<ArgParserException>().having((e) => e.message,
+                  'message', 'Option username is mandatory.')));
         });
 
         test('throw if no mandatory args', () {
@@ -604,7 +607,10 @@ void main() {
           parser.addOption('username', mandatory: true);
           var results = parser.parse(['--test', 'test']);
           expect(results['test'], equals('test'));
-          expect(() => results['username'], throwsA(isA<ArgumentError>()));
+          expect(
+              () => results['username'],
+              throwsA(isA<ArgParserException>().having((e) => e.message,
+                  'message', 'Option username is mandatory.')));
         });
 
         test('parse successfully', () {
@@ -620,8 +626,9 @@ void main() {
           parser.addOption('test', mandatory: true);
           var results = parser.parse(['-h']);
           expect(results['help'], true);
-          expect(() => results['test'], throwsA(isA<ArgumentError>()));
-          expect(() => results.option('test'), throwsA(isA<ArgumentError>()));
+          expect(() => results['test'], throwsA(isA<ArgParserException>()));
+          expect(
+              () => results.option('test'), throwsA(isA<ArgParserException>()));
         });
       });
     });