[Rgen] Add code needed to parse the several snippet attrs.

Allow the transformer to detect this. We will need to think a way to
port them to the new API style.

src/rgen/Microsoft.Macios.Transformer/Attributes/SnippetData.cs

@@ -0,0 +1,97 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+using System.Diagnostics.CodeAnalysis;
+using Microsoft.CodeAnalysis;
+
+namespace Microsoft.Macios.Transformer.Attributes;
+
+readonly struct SnippetData : IEquatable<SnippetData> {
+
+	public string Code { get; }
+
+	public bool Optimizable { get; }
+
+	public SnippetData (string code)
+	{
+		Code = code;
+	}
+
+	public SnippetData (string code, bool optimizable)
+	{
+		Code = code;
+		Optimizable = optimizable;
+	}
+
+	public static bool TryParse (AttributeData attributeData,
+		[NotNullWhen (true)] out SnippetData? data)
+	{
+		data = null;
+		var count = attributeData.ConstructorArguments.Length;
+		string code;
+		var optimizable = false;
+
+		// custom marshal directive values
+
+		switch (count) {
+		case 1:
+			code = (string) attributeData.ConstructorArguments [0].Value!;
+			break;
+		default:
+			// 0 should not be an option..
+			return false;
+		}
+
+		if (attributeData.NamedArguments.Length == 0) {
+			data = new (code);
+			return true;
+		}
+
+		foreach (var (argumentName, value) in attributeData.NamedArguments) {
+			switch (argumentName) {
+			case "Code":
+				code = (string?) value.Value!;
+				break;
+			case "Optimizable":
+				optimizable = (bool) value.Value!;
+				break;
+			default:
+				data = null;
+				return false;
+			}
+		}
+
+		data = new (code, optimizable); 
+		return true;
+	}
+
+	public bool Equals (SnippetData other)
+	{
+		if (Code != other.Code)
+			return false;
+		return Optimizable == other.Optimizable;
+	}
+
+	/// <inheritdoc />
+	public override bool Equals (object? obj)
+	{
+		return obj is SnippetData other && Equals (other);
+	}
+
+	/// <inheritdoc />
+	public override int GetHashCode ()
+		=> HashCode.Combine (Code, Optimizable);
+
+	public static bool operator == (SnippetData x, SnippetData y)
+	{
+		return x.Equals (y);
+	}
+
+	public static bool operator != (SnippetData x, SnippetData y)
+	{
+		return !(x == y);
+	}
+
+	public override string ToString ()
+		=> $"{{ Code: '{Code}' Optimizable: {Optimizable} }}";
+}

src/rgen/Microsoft.Macios.Transformer/AttributesNames.cs

@@ -83,7 +83,13 @@ static class AttributesNames {
 	[BindingFlag (AttributeTargets.Parameter | AttributeTargets.Property)]
 	public const string DisableZeroCopyAttribute = "DisableZeroCopyAttribute";
 
+	/// <summary>
+	/// Code to run from a generated Dispose method, before any generated code is executed
+	/// Adding this attribute will, by default, make the method non-optimizable by the SDK tools
+	/// </summary>
+	[BindingAttribute(typeof(ErrorDomainData), AttributeTargets.Interface | AttributeTargets.Class)]
 	public const string DisposeAttribute = "DisposeAttribute";
+
 	public const string EditorBrowsableAttribute = "System.ComponentModel.EditorBrowsableAttribute";
 
 	[BindingAttribute(typeof(ErrorDomainData), AttributeTargets.Enum)]
@@ -220,6 +226,20 @@ static class AttributesNames {
 	[BindingFlag]
 	public const string PlainStringAttribute = "PlainStringAttribute";
 
+	/// <summary>
+	/// PostSnippet code is inserted before returning, before paramters are disposed/released
+	/// Adding this attribute will, by default, make the method non-optimizable by the SDK tools
+	/// </summary>
+	[BindingAttribute (typeof(SnippetData), AttributeTargets.Method | AttributeTargets.Property)]
+	public const string PostSnippetAttribute = "PostSnippetAttribute";
+
+	/// <summary>
+	/// PreSnippet code is inserted after the parameters have been validated/marshalled
+	/// Adding this attribute will, by default, make the method non-optimizable by the SDK tools
+	/// </summary>
+	[BindingAttribute (typeof(SnippetData), AttributeTargets.Method | AttributeTargets.Property)]
+	public const string PreSnippetAttribute = "PreSnippetAttribute";
+
 	/// <summary>
 	/// When this attribute is applied to the interface definition it will flag the default constructor as private.
 	/// </summary>
@@ -228,6 +248,13 @@ static class AttributesNames {
 
 	[BindingFlag (AttributeTargets.Property)]
 	public const string ProbePresenceAttribute = "ProbePresenceAttribute";
+
+	/// <summary>
+	/// PrologueSnippet code is inserted before any code is generated
+	/// Adding this attribute will, by default, make the method non-optimizable by the SDK tools
+	/// </summary>
+	[BindingAttribute (typeof(SnippetData), AttributeTargets.Method | AttributeTargets.Property)]
+	public const string PrologueSnippetAttribute = "PrologueSnippetAttribute";
 
 	/// <summary>
 	/// Use this attribute to instruct the binding generator that the binding for this particular method should be

tests/rgen/Microsoft.Macios.Transformer.Tests/Attributes/SnippetDataTests.cs

@@ -0,0 +1,62 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+using System.Collections;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+using Microsoft.Macios.Generator.Extensions;
+using Microsoft.Macios.Transformer.Attributes;
+using Xamarin.Tests;
+using Xamarin.Utils;
+
+namespace Microsoft.Macios.Transformer.Tests.Attributes;
+
+public class SnippetDataTests : BaseTransformerTestClass {
+	class TestDataTryCreate : IEnumerable<object []> {
+
+		public IEnumerator<object []> GetEnumerator ()
+		{
+			const string path = "/some/random/path.cs";
+
+			const string disposeAttribute = @"
+using System;
+using Foundation;
+using ObjCRuntime;
+using UIKit;
+
+namespace Test;
+
+[BaseType (typeof (NSControl))]
+[Dispose (""dispatcher = null;"", Optimizable = true)]
+interface NSButton { }
+";
+
+			yield return [(Source: disposeAttribute, Path: path), new SnippetData("dispatcher = null;", true)];
+		}
+
+		IEnumerator IEnumerable.GetEnumerator () => GetEnumerator ();
+	}
+
+	[Theory]
+	[AllSupportedPlatformsClassData<TestDataTryCreate>]
+	void TryCreateTests (ApplePlatform platform, (string Source, string Path) source, SnippetData expectedData)
+	{
+		// create a compilation used to create the transformer
+		var compilation = CreateCompilation (platform, sources: source);
+		var syntaxTree = compilation.SyntaxTrees.ForSource (source);
+		Assert.NotNull (syntaxTree);
+
+		var semanticModel = compilation.GetSemanticModel (syntaxTree);
+		Assert.NotNull (semanticModel);
+
+		var declaration = syntaxTree.GetRoot ()
+			.DescendantNodes ().OfType<BaseTypeDeclarationSyntax> ()
+			.FirstOrDefault ();
+		Assert.NotNull (declaration);
+
+		var symbol = semanticModel.GetDeclaredSymbol (declaration);
+		Assert.NotNull (symbol);
+		var attribute = symbol.GetAttribute<SnippetData> (AttributesNames.DisposeAttribute, SnippetData.TryParse);
+		Assert.Equal (expectedData, attribute);
+	}
+}