Preserve XML documentation in generated commands

Added support to extract and include XML documentation comments from method symbols into the generated command properties. This helps retain developer documentation in the generated code for better maintainability and IntelliSense support.

Author: ChrisPulman

src/ReactiveUI.SourceGenerators.Roslyn/ReactiveCommand/Models/CommandInfo.cs

@@ -19,7 +19,8 @@ internal record CommandInfo(
     CanExecuteTypeInfo? CanExecuteTypeInfo,
     string? OutputScheduler,
     EquatableArray<string> ForwardedPropertyAttributes,
-    string AccessModifier)
+    string AccessModifier,
+    string? XmlComment)
 {
     private const string UnitTypeName = "global::System.Reactive.Unit";
 

src/ReactiveUI.SourceGenerators.Roslyn/ReactiveCommand/ReactiveCommandGenerator.Execute.cs

@@ -123,6 +123,19 @@ public partial class ReactiveCommandGenerator
 
         token.ThrowIfCancellationRequested();
 
+        var xmlTrivia = methodSymbol.GetDocumentationCommentXml(cancellationToken: token);
+
+        // Remove Member attributes from xmlTrivia on the first and last lines
+        if (xmlTrivia?.Length > 0)
+        {
+            var s = xmlTrivia.Split('\n').ToList();
+            s.RemoveAt(0);
+            s.Remove(s.Last());
+            s.Remove(s.Last());
+            xmlTrivia = string.Concat(s.Select(c => "        /// " + c.TrimStart() + "\n"));
+            xmlTrivia = xmlTrivia.TrimEnd();
+        }
+
         return new(
             targetInfo,
             symbol.Name,
@@ -135,7 +148,8 @@ public partial class ReactiveCommandGenerator
             canExecuteTypeInfo,
             outputScheduler,
             forwardedPropertyAttributes,
-            accessModifier);
+            accessModifier,
+            xmlTrivia);
     }
 
     private static string GenerateSource(string containingTypeName, string containingNamespace, string containingClassVisibility, string containingType, CommandInfo[] commands)
@@ -217,6 +231,7 @@ private static string GetCommandSyntax(CommandInfo commandExtensionInfo)
 $$"""
         private {{RxCmd}}<{{inputType}}, {{outputType}}>? {{fieldName}};
 
+{{commandExtensionInfo.XmlComment}}
         [global::System.CodeDom.Compiler.GeneratedCode("{{GeneratorName}}", "{{GeneratorVersion}}")]
         {{forwardedPropertyAttributesString}}
         {{commandExtensionInfo.AccessModifier}} {{RxCmd}}<{{inputType}}, {{outputType}}> {{commandName}} { get => {{initializer}} }