(#606) added ExceptionHandler to ICommandAppSettings

So exceptions can be handled in Spectre.Console.Cli.
Also, some documentation was added.

src/Spectre.Console/Cli/CommandApp.cs

@@ -103,6 +103,11 @@ namespace Spectre.Console.Cli
                     throw;
                 }
 
+                if (_configurator.Settings.ExceptionHandler != null)
+                {
+                    return _configurator.Settings.ExceptionHandler(ex);
+                }
+
                 // Render the exception.
                 var pretty = GetRenderableErrorMessage(ex);
                 if (pretty != null)

src/Spectre.Console/Cli/ConfiguratorExtensions.cs

@@ -224,5 +224,39 @@ namespace Spectre.Console.Cli
 
             return configurator.AddDelegate<TSettings>(name, (c, _) => func(c));
         }
+
+        /// <summary>
+        /// Sets the ExceptionsHandler.
+        /// <para>Setting <see cref="ICommandAppSettings.ExceptionHandler"/> this way will use the
+        /// default exit code of -1.</para>
+        /// </summary>
+        /// <param name="configurator">The configurator.</param>
+        /// <param name="exceptionHandler">The Action that handles the exception.</param>
+        /// <returns>A configurator that can be used to configure the application further.</returns>
+        public static IConfigurator SetExceptionHandler(this IConfigurator configurator, Action<Exception> exceptionHandler)
+        {
+            return configurator.SetExceptionHandler(ex =>
+            {
+                exceptionHandler(ex);
+                return -1;
+            });
+        }
+
+        /// <summary>
+        /// Sets the ExceptionsHandler.
+        /// </summary>
+        /// <param name="configurator">The configurator.</param>
+        /// <param name="exceptionHandler">The Action that handles the exception.</param>
+        /// <returns>A configurator that can be used to configure the application further.</returns>
+        public static IConfigurator SetExceptionHandler(this IConfigurator configurator, Func<Exception, int>? exceptionHandler)
+        {
+            if (configurator == null)
+            {
+                throw new ArgumentNullException(nameof(configurator));
+            }
+
+            configurator.Settings.ExceptionHandler = exceptionHandler;
+            return configurator;
+        }
     }
 }

src/Spectre.Console/Cli/ICommandAppSettings.cs

@@ -1,3 +1,5 @@
+using System;
+
 namespace Spectre.Console.Cli
 {
     /// <summary>
@@ -43,6 +45,8 @@ namespace Spectre.Console.Cli
 
         /// <summary>
         /// Gets or sets a value indicating whether or not exceptions should be propagated.
+        /// <para>Setting this to <c>true</c> will disable default Exception handling and
+        /// any <see cref="ExceptionHandler"/>, if set.</para>
         /// </summary>
         bool PropagateExceptions { get; set; }
 
@@ -50,5 +54,11 @@ namespace Spectre.Console.Cli
         /// Gets or sets a value indicating whether or not examples should be validated.
         /// </summary>
         bool ValidateExamples { get; set; }
+
+        /// <summary>
+        /// Gets or sets a handler for Exceptions.
+        /// <para>This handler will not be called, if <see cref="PropagateExceptions"/> is set to <c>true</c>.</para>
+        /// </summary>
+        public Func<Exception, int>? ExceptionHandler { get; set; }
     }
 }

src/Spectre.Console/Cli/Internal/Configuration/CommandAppSettings.cs

@@ -17,6 +17,8 @@ namespace Spectre.Console.Cli
         public ParsingMode ParsingMode =>
             StrictParsing ? ParsingMode.Strict : ParsingMode.Relaxed;
 
+        public Func<Exception, int>? ExceptionHandler { get; set; }
+
         public CommandAppSettings(ITypeRegistrar registrar)
         {
             Registrar = new TypeRegistrar(registrar);