Make CLI parser public for dotnet nuget why (#6118)

src/NuGet.Core/NuGet.CommandLine.XPlat/Commands/Why/WhyCommand.cs

@@ -10,7 +10,7 @@
 
 namespace NuGet.CommandLine.XPlat.Commands.Why
 {
-    internal static class WhyCommand
+    public static class WhyCommand
     {
         internal static void Register(CommandLineApplication app)
         {
@@ -25,6 +25,16 @@ internal static void Register(CliCommand rootCommand, Func<ILoggerWithColor> get
             Register(rootCommand, getLogger, WhyCommandRunner.ExecuteCommand);
         }
 
+        /// <summary>
+        /// This is a temporary API until NuGet migrates all our commands to System.CommandLine, at which time I suspect we'll have a NuGetParser.GetNuGetCommand for all the `dotnet nuget *` commands.
+        /// For now, this allows the dotnet CLI to invoke why directly, instead of running NuGet.CommandLine.XPlat as a child process.
+        /// </summary>
+        /// <param name="rootCommand">The <c>dotnet nuget</c> command handler, to add <c>why</c> to.</param>
+        public static void GetWhyCommand(CliCommand rootCommand)
+        {
+            Register(rootCommand, CommandOutputLogger.Create, WhyCommandRunner.ExecuteCommand);
+        }
+
         internal static void Register(CliCommand rootCommand, Func<ILoggerWithColor> getLogger, Func<WhyCommandArgs, int> action)
         {
             var whyCommand = new CliCommand("why", Strings.WhyCommand_Description);

src/NuGet.Core/NuGet.CommandLine.XPlat/PublicAPI.Unshipped.txt

@@ -0,0 +1,2 @@
+NuGet.CommandLine.XPlat.Commands.Why.WhyCommand
+static NuGet.CommandLine.XPlat.Commands.Why.WhyCommand.GetWhyCommand(System.CommandLine.CliCommand rootCommand) -> void

src/NuGet.Core/NuGet.CommandLine.XPlat/Utility/CommandOutputLogger.cs

@@ -19,6 +19,17 @@ public CommandOutputLogger(LogLevel logLevel)
             VerbosityLevel = logLevel;
         }
 
+        /// <summary>
+        /// Create a CommandOutputLogger for commands invoked by the .NET CLI
+        /// </summary>
+        /// <returns></returns>
+        public static CommandOutputLogger Create()
+        {
+            var logger = new CommandOutputLogger(LogLevel.Information);
+            logger.HidePrefixForInfoAndMinimal = true;
+            return logger;
+        }
+
         public override void LogDebug(string data)
         {
             LogInternal(LogLevel.Debug, data);