Only display usages when no default value has been specified.

Fixes #60

Author: Matthiee

CommandLineParser.Tests/Usage/UsagePrinterTests.cs

@@ -12,6 +12,38 @@ namespace MatthiWare.CommandLine.Tests.Usage
 {
     public class UsagePrinterTests
     {
+        #region Issue_60
+
+        private class Options_Issue60
+        {
+            [Name("c", "check")]
+            [Description("Reports the amount of duplicates without changing anything")]
+            [DefaultValue(true)] // Note defaults to true and not required
+            public bool OnlyCheck { get; set; }
+        }
+
+        [Theory]
+        // https://github.com/MatthiWare/CommandLineParser.Core/issues/60
+        [InlineData(new string[] { }, false)]
+        [InlineData(new string[] { "-c" }, false)]
+        [InlineData(new string[] { "-c", "true" }, false)]
+        [InlineData(new string[] { "-c", "false" }, false)]
+        public void AllOptionsHaveDefaultValueShouldNotPrintUsages(string[] args, bool called)
+        {
+            var printerMock = new Mock<IUsagePrinter>();
+
+            var parser = new CommandLineParser<Options_Issue60>
+            {
+                Printer = printerMock.Object
+            };
+
+            parser.Parse(args);
+
+            printerMock.Verify(mock => mock.PrintUsage(), called ? Times.Once() : Times.Never());
+        }
+
+        #endregion
+
         private class UsagePrinterGetsCalledOptions
         {
             [Name("o"), Required]

CommandLineParser/CommandLineParser`TOption.cs

@@ -306,7 +306,7 @@ private void AutoPrintUsageAndErrors(ParseResult<TOption> result, bool noArgsSup
         {
             if (!ParserOptions.AutoPrintUsageAndErrors) return;
 
-            if (noArgsSupplied)
+            if (noArgsSupplied && (Options.Any(opt => !opt.HasDefault) || Commands.Any(cmd => cmd.IsRequired)))
                 PrintHelp();
             else if (result.HelpRequested)
                 Printer.PrintUsage(result.HelpRequestedFor);