[Rgen] Use the formatter pattern for the SmartEnum extension class de…

…claration. (#21900)

Use the same pattern as with other declarations

---------

Co-authored-by: GitHub Actions Autoformatter <[email protected]>
Co-authored-by: Michael Cummings (MSFT) <[email protected]>

src/rgen/Microsoft.Macios.Generator/Emitters/EnumEmitter.cs

@@ -4,6 +4,7 @@
 using Microsoft.CodeAnalysis;
 using Microsoft.Macios.Generator.Context;
 using Microsoft.Macios.Generator.DataModel;
+using Microsoft.Macios.Generator.Formatters;
 
 namespace Microsoft.Macios.Generator.Emitters;
 
@@ -139,8 +140,9 @@ public bool TryEmit (in BindingContext bindingContext, [NotNullWhen (false)] out
 
 		bindingContext.Builder.AppendMemberAvailability (bindingContext.Changes.SymbolAvailability);
 		bindingContext.Builder.AppendGeneratedCodeAttribute ();
-		var modifiers = $"{string.Join (' ', bindingContext.Changes.Modifiers)} ";
-		using (var classBlock = bindingContext.Builder.CreateBlock ($"{(string.IsNullOrWhiteSpace (modifiers) ? string.Empty : modifiers)}static partial class {GetSymbolName (bindingContext.Changes)}", true)) {
+		var extensionClassDeclaration =
+			bindingContext.Changes.ToSmartEnumExtensionDeclaration (GetSymbolName (bindingContext.Changes));
+		using (var classBlock = bindingContext.Builder.CreateBlock (extensionClassDeclaration.ToString (), true)) {
 			classBlock.AppendLine ();
 			classBlock.AppendLine ($"static IntPtr[] values = new IntPtr [{bindingContext.Changes.EnumMembers.Length}];");
 			// foreach member in the enum we need to create a field that holds the value, the property emitter

src/rgen/Microsoft.Macios.Generator/Formatters/SmartEnumFormatter.cs

@@ -0,0 +1,44 @@
+using System.Collections.Generic;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.Macios.Generator.DataModel;
+using static Microsoft.CodeAnalysis.CSharp.SyntaxFactory;
+
+namespace Microsoft.Macios.Generator.Formatters;
+
+static class SmartEnumFormatter {
+	/// <summary>
+	/// Return the declaration of the extension class for a given smart enum using the provided class name.
+	/// </summary>
+	/// <param name="smartEnumChange">The smart enum code change.</param>
+	/// <param name="extensionClassName">The name to use for the extension class.</param>
+	/// <returns>The class declaration for the extension class for a smart enum change.</returns>
+	public static CompilationUnitSyntax ToSmartEnumExtensionDeclaration (this in CodeChanges smartEnumChange,
+		string extensionClassName)
+	{
+		// add to a set to make sure we do no duplicate them and make sure static and partial are present 
+		var modifiers = new HashSet<SyntaxToken> (smartEnumChange.Modifiers) {
+			Token (SyntaxKind.StaticKeyword), Token (SyntaxKind.PartialKeyword),
+		};
+
+		var compilationUnit = CompilationUnit ().WithMembers (
+				SingletonList<MemberDeclarationSyntax> (
+					ClassDeclaration (extensionClassName)
+						.WithModifiers (TokenList (modifiers))
+						.WithOpenBraceToken (MissingToken (SyntaxKind.OpenBraceToken)) // do not add open/close brace
+						.WithCloseBraceToken (MissingToken (SyntaxKind.CloseBraceToken))))
+			.NormalizeWhitespace (); // no diff between dotnet and mono
+		return compilationUnit;
+	}
+
+	/// <summary>
+	/// Return the declaration of the extension class for a given smart enum using the provided class name.
+	/// </summary>
+	/// <param name="smartEnumChange">The smart enum code change.</param>
+	/// <param name="extensionClassName">The name to use for the extension class.</param>
+	/// <returns>The class declaration for the extension class for a smart enum change.</returns>
+	public static CompilationUnitSyntax? ToSmartEnumExtensionDeclaration (this in CodeChanges? smartEnumChange,
+		string extensionClassName)
+		=> smartEnumChange is null ? null : ToSmartEnumExtensionDeclaration (smartEnumChange.Value, extensionClassName);
+}

tests/rgen/Microsoft.Macios.Generator.Tests/Formatters/SmartEnumFormatterTests.cs

@@ -0,0 +1,81 @@
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.Macios.Generator.DataModel;
+using Microsoft.Macios.Generator.Formatters;
+using Xamarin.Tests;
+using Xamarin.Utils;
+using Xunit;
+
+namespace Microsoft.Macios.Generator.Tests.Formatters;
+
+public class SmartEnumFormatterTests : BaseGeneratorTestClass {
+
+	class TestDataToExtensionDeclaration : IEnumerable<object []> {
+		public IEnumerator<object []> GetEnumerator ()
+		{
+			const string publicSmartEnum = @"
+using System;
+using Foundation;
+using ObjCBindings;
+
+namespace AVFoundation;
+
+[BindingType]
+public enum AVCaptureDeviceType {
+
+	[Field<EnumValue> (""AVCaptureDeviceTypeBuiltInMicrophone"")]
+	BuiltInMicrophone,
+
+	[Field<EnumValue> (""AVCaptureDeviceTypeBuiltInWideAngleCamera"")]
+	BuiltInWideAngleCamera,
+}
+";
+			yield return [publicSmartEnum, "AVCaptureDeviceTypeExtensions", "public static partial class AVCaptureDeviceTypeExtensions"];
+
+			const string internalSmartEnum = @"
+using System;
+using Foundation;
+using ObjCBindings;
+
+namespace AVFoundation;
+
+[BindingType]
+internal enum AVCaptureDeviceType {
+
+	[Field<EnumValue> (""AVCaptureDeviceTypeBuiltInMicrophone"")]
+	BuiltInMicrophone,
+
+	[Field<EnumValue> (""AVCaptureDeviceTypeBuiltInWideAngleCamera"")]
+	BuiltInWideAngleCamera,
+}
+";
+
+			yield return [internalSmartEnum, "AVCaptureDeviceTypeExtensions", "internal static partial class AVCaptureDeviceTypeExtensions"];
+		}
+
+		IEnumerator IEnumerable.GetEnumerator () => GetEnumerator ();
+	}
+
+	[Theory]
+	[AllSupportedPlatformsClassData<TestDataToExtensionDeclaration>]
+	public void ToDeclarationTests (ApplePlatform platform, string inputText, string className, string expectedDeclaration)
+	{
+		var (compilation, syntaxTrees) = CreateCompilation (platform, sources: inputText);
+		Assert.Single (syntaxTrees);
+		var declaration = syntaxTrees [0].GetRoot ()
+			.DescendantNodes ()
+			.OfType<EnumDeclarationSyntax> ()
+			.FirstOrDefault ();
+		Assert.NotNull (declaration);
+		var semanticModel = compilation.GetSemanticModel (syntaxTrees [0]);
+		Assert.NotNull (semanticModel);
+		var changes = CodeChanges.FromDeclaration (declaration, semanticModel);
+		Assert.NotNull (changes);
+		var classDeclaration = changes.ToSmartEnumExtensionDeclaration (className);
+		Assert.NotNull (classDeclaration);
+		var str = classDeclaration.ToString ();
+		Assert.Equal (expectedDeclaration, classDeclaration.ToString ());
+	}
+}