refactor: Remove Get/Set Description on Helper subsystem

Add Get to AnnotationAccessor

Author: BenjaminMichaelis

src/System.CommandLine.Subsystems.Tests/AlternateSubsystems.cs

@@ -2,8 +2,6 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System.CommandLine.Directives;
-using System.CommandLine.Subsystems;
-using System.CommandLine.Subsystems.Annotations;
 
 namespace System.CommandLine.Subsystems.Tests
 {
@@ -33,7 +31,7 @@ public VersionThatUsesHelpData(CliSymbol symbol)
             protected override CliExit Execute(PipelineContext pipelineContext)
             {
                 var help = pipelineContext.Pipeline.Help ?? throw new InvalidOperationException("Help cannot be null for this subsystem to work");
-                var data = help.GetDescription(Symbol);
+                string data = help.Description.Get(Symbol);
 
                 pipelineContext.ConsoleHack.WriteLine(data);
                 pipelineContext.AlreadyHandled = true;
@@ -68,11 +66,11 @@ protected override CliExit TearDown(CliExit cliExit)
         }
 
         internal class StringDirectiveSubsystem(IAnnotationProvider? annotationProvider = null)
-           : DirectiveSubsystem("other",SubsystemKind.Diagram, annotationProvider)
+           : DirectiveSubsystem("other", SubsystemKind.Diagram, annotationProvider)
         { }
 
         internal class BooleanDirectiveSubsystem(IAnnotationProvider? annotationProvider = null)
-           : DirectiveSubsystem("diagram", SubsystemKind.Diagram,  annotationProvider)
+           : DirectiveSubsystem("diagram", SubsystemKind.Diagram, annotationProvider)
         { }
 
     }

src/System.CommandLine.Subsystems/HelpSubsystem.cs

@@ -1,4 +1,4 @@
-// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System.CommandLine.Subsystems.Annotations;
@@ -24,14 +24,6 @@ public class HelpSubsystem(IAnnotationProvider? annotationProvider = null)
         Arity = ArgumentArity.Zero
     };
 
-    public void SetDescription(CliSymbol symbol, string description)
-        => SetAnnotation(symbol, HelpAnnotations.Description, description);
-
-    public string GetDescription(CliSymbol symbol)
-        => TryGetAnnotation<string>(symbol, HelpAnnotations.Description, out var value)
-            ? value
-            : "";
-
     public AnnotationAccessor<string> Description
         => new(this, HelpAnnotations.Description);
 

src/System.CommandLine.Subsystems/Subsystems/Annotations/AnnotationAccessor.cs

@@ -8,12 +8,20 @@ namespace System.CommandLine.Subsystems.Annotations;
 /// <summary>
 /// Allows associating an annotation with a <see cref="CliSymbol"/>. The annotation will be stored by the accessor's owner <see cref="CliSubsystem"/>.
 /// </summary>
-public struct AnnotationAccessor<TValue>(CliSubsystem owner, AnnotationId<TValue> id)
+public struct AnnotationAccessor<TValue>(CliSubsystem owner, AnnotationId<TValue> id, TValue? defaultValue = default)
 {
     /// <summary>
     /// The ID of the annotation
     /// </summary>
     public AnnotationId<TValue> Id { get; }
     public readonly void Set(CliSymbol symbol, TValue value) => owner.SetAnnotation(symbol, id, value);
     public readonly bool TryGet(CliSymbol symbol, [NotNullWhen(true)] out TValue? value) => owner.TryGetAnnotation(symbol, id, out value);
+    public readonly TValue? Get(CliSymbol symbol)
+    {
+        if (TryGet(symbol, out var value))
+        {
+            return value ?? defaultValue;
+        }
+        return defaultValue;
+    }
 }