Validate option name length

Closes #40

CliFx.Tests/ApplicationSpecs.Commands.cs

@@ -76,6 +76,24 @@ namespace CliFx.Tests
             public ValueTask ExecuteAsync(IConsole console) => default;
         }
 
+        [Command]
+        private class EmptyOptionNameCommand : ICommand
+        {
+            [CommandOption("")]
+            public string? Apples { get; set; }
+
+            public ValueTask ExecuteAsync(IConsole console) => default;
+        }
+
+        [Command]
+        private class SingleCharacterOptionNameCommand : ICommand
+        {
+            [CommandOption("a")]
+            public string? Apples { get; set; }
+
+            public ValueTask ExecuteAsync(IConsole console) => default;
+        }
+
         [Command]
         private class DuplicateOptionNamesCommand : ICommand
         {

CliFx.Tests/ApplicationSpecs.cs

@@ -125,6 +125,26 @@ namespace CliFx.Tests
             Assert.Throws<CliFxException>(() => ApplicationSchema.Resolve(commandTypes));
         }
 
+        [Fact]
+        public void Command_options_must_have_names_that_are_not_empty()
+        {
+            // Arrange
+            var commandTypes = new[] {typeof(EmptyOptionNameCommand)};
+
+            // Act & assert
+            Assert.Throws<CliFxException>(() => ApplicationSchema.Resolve(commandTypes));
+        }
+
+        [Fact]
+        public void Command_options_must_have_names_that_are_longer_than_one_character()
+        {
+            // Arrange
+            var commandTypes = new[] {typeof(SingleCharacterOptionNameCommand)};
+
+            // Act & assert
+            Assert.Throws<CliFxException>(() => ApplicationSchema.Resolve(commandTypes));
+        }
+
         [Fact]
         public void Command_options_must_have_unique_names()
         {

CliFx/Attributes/CommandOptionAttribute.cs

@@ -9,14 +9,14 @@ namespace CliFx.Attributes
     public class CommandOptionAttribute : Attribute
     {
         /// <summary>
-        /// Option name.
+        /// Option name (must be longer than a single character).
         /// Either <see cref="Name"/> or <see cref="ShortName"/> must be set.
         /// All options in a command must have different names (comparison is not case-sensitive).
         /// </summary>
         public string? Name { get; }
 
         /// <summary>
-        /// Option short name.
+        /// Option short name (single character).
         /// Either <see cref="Name"/> or <see cref="ShortName"/> must be set.
         /// All options in a command must have different short names (comparison is case-sensitive).
         /// </summary>

CliFx/Domain/ApplicationSchema.cs

@@ -163,6 +163,35 @@ namespace CliFx.Domain
 
         private static void ValidateOptions(CommandSchema command)
         {
+            var emptyNameGroup = command.Options
+                .Where(o => o.ShortName == null && string.IsNullOrWhiteSpace(o.Name))
+                .ToArray();
+
+            if (emptyNameGroup.Any())
+            {
+                throw new CliFxException(new StringBuilder()
+                    .AppendLine($"Command {command.Type.FullName} contains one or more options that have empty names:")
+                    .AppendBulletList(emptyNameGroup.Select(o => o.Property.Name))
+                    .AppendLine()
+                    .Append("Options in a command must all have at least a name or a short name.")
+                    .ToString());
+            }
+
+            var invalidNameGroup = command.Options
+                .Where(o => !string.IsNullOrWhiteSpace(o.Name))
+                .Where(o => o.Name.Length <= 1)
+                .ToArray();
+
+            if (invalidNameGroup.Any())
+            {
+                throw new CliFxException(new StringBuilder()
+                    .AppendLine($"Command {command.Type.FullName} contains one or more options that have names that are too short:")
+                    .AppendBulletList(invalidNameGroup.Select(o => o.Property.Name))
+                    .AppendLine()
+                    .Append("Options in a command must all have names that are longer than a single character.")
+                    .ToString());
+            }
+
             var duplicateNameGroup = command.Options
                 .Where(o => !string.IsNullOrWhiteSpace(o.Name))
                 .GroupBy(o => o.Name, StringComparer.OrdinalIgnoreCase)