fix: reset state of commandline app, args, and options on each call of .Parse

Fixes #253

Author: natemcmaster

src/CommandLineUtils/CommandArgument.cs

@@ -59,5 +59,10 @@ public CommandArgument()
         /// When validation fails, <see cref="CommandLineApplication.ValidationErrorHandler"/> is invoked.
         /// </summary>
         public ICollection<IArgumentValidator> Validators { get; } = new List<IArgumentValidator>();
+
+        internal void Reset()
+        {
+            Values.Clear();
+        }
     }
 }

src/CommandLineUtils/CommandLineApplication.cs

@@ -707,6 +707,27 @@ public void OnExecuteAsync(Func<CancellationToken, Task<int>> invoke)
             _handler = invoke;
         }
 
+        private void Reset()
+        {
+            foreach (var arg in Arguments)
+            {
+                arg.Reset();
+            }
+
+            foreach (var option in Options)
+            {
+                option.Reset();
+            }
+
+            foreach (var cmd in Commands)
+            {
+                cmd.Reset();
+            }
+
+            IsShowingInformation = default;
+            RemainingArguments.Clear();
+        }
+
         /// <summary>
         /// Adds an action to be invoked when all command line arguments have been parsed and validated.
         /// </summary>
@@ -729,6 +750,8 @@ public void OnParsingComplete(Action<ParseResult> action)
         /// <returns>The result of parsing.</returns>
         public ParseResult Parse(params string[] args)
         {
+            Reset();
+
             args ??= Util.EmptyArray<string>();
 
             var processor = new CommandLineProcessor(this, args);

src/CommandLineUtils/CommandOption.cs

@@ -244,5 +244,10 @@ private bool IsEnglishLetter(char c)
         {
             return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z');
         }
+
+        internal void Reset()
+        {
+            Values.Clear();
+        }
     }
 }

test/CommandLineUtils.Tests/CommandLineApplicationTests.cs

@@ -21,6 +21,29 @@ public CommandLineApplicationTests(ITestOutputHelper output)
             _output = output;
         }
 
+        [Fact]
+        public void CommandLineAppCanBeCalledTwice()
+        {
+            var app = new CommandLineApplication(new TestConsole(_output));
+            var helpOption = app.HelpOption(inherited: true);
+            var verboseOption = app.VerboseOption();
+            var subcmd = app.Command("test", _ => { });
+
+            app.Execute("test", "--help");
+            Assert.True(app.IsShowingInformation);
+            Assert.True(subcmd.IsShowingInformation);
+            Assert.True(helpOption.HasValue());
+
+            app.Execute("-vvv");
+            Assert.False(app.IsShowingInformation);
+            Assert.False(subcmd.IsShowingInformation);
+            Assert.False(helpOption.HasValue());
+            Assert.Equal(3, verboseOption.Values.Count);
+
+            app.Execute("test");
+            Assert.Empty(verboseOption.Values);
+        }
+
         [Fact]
         public void CommandNameCanBeMatched()
         {