ICommandLineValidatable back as it was, but now with support for CommandLineValidationException

Author: rstarkov

Src/CommandLineParser.cs

@@ -498,14 +498,18 @@ private static object parseCommandLine(string[] args, Type type, int i, Func<Con
         if (missingMandatories.Count > 0)
             throw new MissingParameterException(missingMandatories[0], swallowingField, !missingMandatories[0].IsDefined<IsPositionalAttribute>(), getHelpGenerator(type, helpProcessor));
 
-        try
-        {
-            if (ret is ICommandLineProcessed v)
-                v.Process();
-        }
-        catch (CommandLineValidationException exc) when (exc.GenerateHelpFunc == null)
+        if (ret is ICommandLineValidatable v)
         {
-            throw new CommandLineValidationException(exc.ColoredMessage, getHelpGenerator(type, helpProcessor));
+            try
+            {
+                var error = v.Validate();
+                if (error != null)
+                    throw new CommandLineValidationException(error, getHelpGenerator(type, helpProcessor));
+            }
+            catch (CommandLineValidationException exc) when (exc.GenerateHelpFunc == null)
+            {
+                throw new CommandLineValidationException(exc.ColoredMessage, getHelpGenerator(type, helpProcessor));
+            }
         }
 
         return ret;

Src/ICommandLineProcessed.cs

@@ -0,0 +1,24 @@
+using RT.Util.Consoles;
+
+namespace RT.CommandLine;
+
+/// <summary>
+///     Contains methods to validate and post-process a class representing command-line options as populated by <see
+///     cref="CommandLineParser"/>.</summary>
+public interface ICommandLineValidatable
+{
+    /// <summary>
+    ///     When implemented in a class, returns an error message if the contents of the class are invalid, otherwise returns
+    ///     null.</summary>
+    /// <remarks>
+    ///     <para>
+    ///         When <see cref="CommandLineParser"/> invokes this method, all parsed commands and options have already been
+    ///         populated. This method can thus alter the class in application-specific ways, perform further parsing, or
+    ///         further validate the options for constraints such as mutual exclusivity.</para>
+    ///     <para>
+    ///         To report a validation error, this method can either return the text of the error message, or throw a <see
+    ///         cref="CommandLineValidationException"/>. The message is passed to the user in the same way as other parse
+    ///         errors (for example, see <see cref="CommandLineParser.ParseOrWriteUsageToConsole"/> which prints it to the
+    ///         console).</para></remarks>
+    ConsoleColoredString Validate();
+}

Src/ICommandLineValidatable.cs

@@ -4,7 +4,7 @@ namespace RT.CommandLine.Tests;
 
 #pragma warning disable CS0649 // Field is never assigned to and will always have its default value
 
-class Test1Cmd : ICommandLineProcessed
+class Test1Cmd : ICommandLineValidatable
 {
     [IsPositional, IsMandatory]
     public string Base;
@@ -14,17 +14,18 @@ class Test1Cmd : ICommandLineProcessed
 
     public static int ValidateCalled = 0;
 
-    public void Process()
+    public ConsoleColoredString Validate()
     {
         ValidateCalled++;
+        return null;
     }
 }
 
 [CommandGroup]
-abstract class Test1SubcommandBase : ICommandLineProcessed
+abstract class Test1SubcommandBase : ICommandLineValidatable
 {
     public static int ValidateCalled = 0;
-    public abstract void Process();
+    public abstract ConsoleColoredString Validate();
 }
 
 [CommandName("sub1")]
@@ -33,14 +34,15 @@ sealed class Test1Subcommand1 : Test1SubcommandBase
     [IsPositional, IsMandatory]
     public string ItemName;
 
-    public override void Process()
+    public override ConsoleColoredString Validate()
     {
         ValidateCalled++;
+        return null;
     }
 }
 
 [CommandName("sub2")]
 sealed class Test1Subcommand2 : Test1SubcommandBase
 {
-    public override void Process() { }
+    public override ConsoleColoredString Validate() { return null; }
 }