Added support for /help (short form: /?) switch

Author: davkean

src/CodeFormatter/CommandLineParser.cs

@@ -15,6 +15,7 @@ public enum Operation
     {
         Format,
         ListRules,
+        ShowHelp
     }
 
     public sealed class CommandLineOptions
@@ -30,6 +31,18 @@ public sealed class CommandLineOptions
             allowTables: false,
             verbose: false);
 
+        public static readonly CommandLineOptions ShowHelp = new CommandLineOptions(
+            Operation.ShowHelp,
+            ImmutableArray<string[]>.Empty,
+            ImmutableArray<string>.Empty,
+            ImmutableDictionary<string, bool>.Empty,
+            ImmutableArray<string>.Empty,
+            ImmutableArray<string>.Empty,
+            null,
+            allowTables: false,
+            verbose: false);
+
+
         public readonly Operation Operation;
         public readonly ImmutableArray<string[]> PreprocessorConfigurations;
         public readonly ImmutableArray<string> CopyrightHeader;
@@ -143,8 +156,7 @@ containing a custom copyright header.
     /rule(+|-)      - Enable (default) or disable the specified rule
     /rules          - List the available rules
     /verbose        - Verbose output
-
-Use ConvertTests to convert MSTest tests to xUnit.
+    /help           - Displays this usage message (short form: /?)
 ";
 
         public static void PrintUsage()
@@ -245,6 +257,10 @@ public static CommandLineParseResult Parse(string[] args)
                 {
                     return CommandLineParseResult.CreateSuccess(CommandLineOptions.ListRules);
                 }
+                else if (comparer.Equals(arg, "/?") || comparer.Equals(arg, "/help"))
+                {
+                    return CommandLineParseResult.CreateSuccess(CommandLineOptions.ShowHelp);
+                }
                 else if (arg.StartsWith("/", comparison))
                 {
                     return CommandLineParseResult.CreateError($"Unrecognized option \"{arg}\"");

src/CodeFormatter/Program.cs

@@ -31,6 +31,11 @@ private static int Main(string[] args)
             int exitCode;
             switch (options.Operation)
             {
+                case Operation.ShowHelp:
+                    CommandLineParser.PrintUsage();
+                    exitCode = 0;
+                    break;
+
                 case Operation.ListRules:
                     RunListRules();
                     exitCode = 0;

src/Microsoft.DotNet.CodeFormatting.Tests/CommandLineParserTests.cs

@@ -108,6 +108,28 @@ public void NoCopyright()
             Assert.Equal(new[] { "test.csproj" }, options.FormatTargets);
         }
 
+
+        [Fact]
+        public void Help()
+        {
+            var options = Parse("/help");
+            Assert.Equal(options.Operation, Operation.ShowHelp);
+        }
+
+        [Fact]
+        public void HelpShortForm()
+        {
+            var options = Parse("/?");
+            Assert.Equal(options.Operation, Operation.ShowHelp);
+        }
+
+        [Fact]
+        public void HelpWithOtherwiseValidArguments()
+        {
+            var options = Parse("test.csproj", "/nocopyright", "/help");
+            Assert.Equal(options.Operation, Operation.ShowHelp);
+        }
+
         [Fact]
         public void CopyrightEnable1()
         {