[RGen] Keep the track of the enum member position.

src/rgen/Microsoft.Macios.Generator/DataModel/Binding.Generator.cs

@@ -300,7 +300,7 @@ internal Binding (BindingInfo bindingInfo, string name, ImmutableArray<string> @
 		var bucket = ImmutableArray.CreateBuilder<EnumMember> ();
 		// loop over the fields and add those that contain a FieldAttribute
 		var enumValueDeclarations = enumDeclaration.Members.OfType<EnumMemberDeclarationSyntax> ();
-		foreach (var enumValueDeclaration in enumValueDeclarations) {
+		foreach (var (index, enumValueDeclaration) in enumValueDeclarations.Index ()) {
 			if (Skip (enumValueDeclaration, context.SemanticModel))
 				continue;
 			if (context.SemanticModel.GetDeclaredSymbol (enumValueDeclaration) is not IFieldSymbol enumValueSymbol) {
@@ -314,6 +314,7 @@ internal Binding (BindingInfo bindingInfo, string name, ImmutableArray<string> @
 				// could not calculate the library for the enum add it with bad data for the analyzer to pick it up
 				var enumMember = new EnumMember (
 					name: enumValueDeclaration.Identifier.ToFullString ().Trim (),
+					index: (uint) index,
 					libraryName: string.Empty,
 					libraryPath: null,
 					fieldData: enumValueSymbol.GetFieldData (),
@@ -326,6 +327,7 @@ internal Binding (BindingInfo bindingInfo, string name, ImmutableArray<string> @
 			} else {
 				var enumMember = new EnumMember (
 					name: enumValueDeclaration.Identifier.ToFullString ().Trim (),
+					index: (uint) index,
 					libraryName: libraryName,
 					libraryPath: libraryPath,
 					fieldData: enumValueSymbol.GetFieldData (),

src/rgen/Microsoft.Macios.Generator/DataModel/EnumMember.Generator.cs

@@ -30,19 +30,21 @@ readonly partial struct EnumMember {
 	/// Create a new change that happened on a member.
 	/// </summary>
 	/// <param name="name">The name of the changed member.</param>
+	/// <param name="index">The position of the enum member starting at 0.</param>
 	/// <param name="libraryName">The library name of the smart enum.</param>
 	/// <param name="libraryPath">The library path to the library, null if it is a known frameworl.</param>
 	/// <param name="fieldData">The binding data attached to this enum value.</param>
 	/// <param name="symbolAvailability">The symbol availability of the member.</param>
 	/// <param name="attributes">The list of attribute changes in the member.</param>
 	public EnumMember (string name,
+		uint index,
 		string libraryName,
 		string? libraryPath,
 		FieldData<EnumValue>? fieldData,
 		SymbolAvailability symbolAvailability,
-		ImmutableArray<AttributeCodeChange> attributes)
+		ImmutableArray<AttributeCodeChange> attributes) : this (StructState.Initialized, name)
 	{
-		Name = name;
+		Index = index;
 		FieldInfo = fieldData is null ? null : new (fieldData.Value, libraryName, libraryPath);
 		SymbolAvailability = symbolAvailability;
 		Attributes = attributes;
@@ -52,11 +54,13 @@ public EnumMember (string name,
 	/// Create a new change that happened on a member.
 	/// </summary>
 	/// <param name="name">The name of the changed member.</param>
+	/// <param name="index">The position of the enum member starting at 0.</param>
 	/// <param name="libraryName">The library name of the smart enum.</param>
 	/// <param name="libraryPath">The library path to the library, null if it is a known frameworl.</param>
-	public EnumMember (string name, string libraryName, string? libraryPath)
+	public EnumMember (string name, uint index, string libraryName, string? libraryPath)
 		: this (
 			name: name,
+			index: index,
 			libraryName: libraryName,
 			libraryPath: libraryPath,
 			fieldData: null,

src/rgen/Microsoft.Macios.Generator/DataModel/EnumMember.cs

@@ -17,11 +17,32 @@ namespace Microsoft.Macios.Generator.DataModel;
 /// </summary>
 [StructLayout (LayoutKind.Auto)]
 readonly partial struct EnumMember : IEquatable<EnumMember> {
+
+	/// <summary>
+	/// The initialization state of the struct.
+	/// </summary>
+	StructState State { get; init; } = StructState.Default;
+
+	/// <summary>
+	/// Gets the default, uninitialized instance of <see cref="EnumMember"/>.
+	/// </summary>
+	public static EnumMember Default { get; } = new (StructState.Default, string.Empty);
+
+	/// <summary>
+	/// Gets a value indicating whether the instance is the default, uninitialized instance.
+	/// </summary>
+	public bool IsNullOrDefault => State == StructState.Default;
+
 	/// <summary>
 	/// Get the name of the member.
 	/// </summary>
 	public string Name { get; }
 
+	/// <summary>
+	/// Gets the index of the enum member.
+	/// </summary>
+	public uint Index { get; init; }
+
 	/// <summary>
 	/// The platform availability of the enum value.
 	/// </summary>
@@ -37,6 +58,8 @@ public bool Equals (EnumMember other)
 	{
 		if (Name != other.Name)
 			return false;
+		if (Index != other.Index)
+			return false;
 		if (SymbolAvailability != other.SymbolAvailability)
 			return false;
 		if (FieldInfo != other.FieldInfo)
@@ -55,24 +78,47 @@ public override bool Equals (object? obj)
 	/// <inheritdoc />
 	public override int GetHashCode ()
 	{
-		return HashCode.Combine (Name, SymbolAvailability, Attributes);
+		return HashCode.Combine (Name, Index, SymbolAvailability, FieldInfo, Attributes);
 	}
 
+	/// <summary>
+	/// Compares two <see cref="EnumMember"/> instances for equality.
+	/// </summary>
+	/// <param name="x">The first <see cref="EnumMember"/> to compare.</param>
+	/// <param name="y">The second <see cref="EnumMember"/> to compare.</param>
+	/// <returns><c>true</c> if the instances are equal; otherwise, <c>false</c>.</returns>
 	public static bool operator == (EnumMember x, EnumMember y)
 	{
 		return x.Equals (y);
 	}
 
+	/// <summary>
+	/// Compares two <see cref="EnumMember"/> instances for inequality.
+	/// </summary>
+	/// <param name="x">The first <see cref="EnumMember"/> to compare.</param>
+	/// <param name="y">The second <see cref="EnumMember"/> to compare.</param>
+	/// <returns><c>true</c> if the instances are not equal; otherwise, <c>false</c>.</returns>
 	public static bool operator != (EnumMember x, EnumMember y)
 	{
 		return !(x == y);
 	}
 
+	/// <summary>
+	/// Initializes a new instance of the <see cref="EnumMember"/> struct.
+	/// </summary>
+	/// <param name="state">The initialization state of the struct.</param>
+	/// <param name="name">The name of the enum member.</param>
+	public EnumMember (StructState state, string name)
+	{
+		State = state;
+		Name = name;
+	}
+
 	/// <inheritdoc />
 	public override string ToString ()
 	{
 		var sb = new StringBuilder (
-			$"{{ Name: '{Name}' SymbolAvailability: {SymbolAvailability} FieldInfo: {FieldInfo} Attributes: [");
+			$"{{ Name: '{Name}', Index: {Index}, SymbolAvailability: {SymbolAvailability} FieldInfo: {FieldInfo} Attributes: [");
 		sb.AppendJoin (", ", Attributes);
 		sb.Append ("] }");
 		return sb.ToString ();

src/rgen/Microsoft.Macios.Transformer/DataModel/Binding.Transformer.cs

@@ -90,7 +90,7 @@ internal Binding (EnumDeclarationSyntax enumDeclaration, INamedTypeSymbol symbol
 		var bindingType = HasErrorDomainAttribute ? BindingType.SmartEnum : BindingType.Unknown;
 		var bucket = ImmutableArray.CreateBuilder<EnumMember> ();
 		var enumValueDeclarations = enumDeclaration.Members.OfType<EnumMemberDeclarationSyntax> ();
-		foreach (var enumValueDeclaration in enumValueDeclarations) {
+		foreach (var (index, enumValueDeclaration) in enumValueDeclarations.Index ()) {
 			if (context.SemanticModel.GetDeclaredSymbol (enumValueDeclaration) is not IFieldSymbol enumValueSymbol) {
 				continue;
 			}
@@ -106,6 +106,7 @@ internal Binding (EnumDeclarationSyntax enumDeclaration, INamedTypeSymbol symbol
 				}
 				enumMember = new EnumMember (
 					name: enumValueDeclaration.Identifier.ToFullString ().Trim (),
+		  index: (uint) index,
 					libraryName: string.Empty,
 					libraryPath: null,
 					fieldData: enumValueSymbol.GetFieldData (),
@@ -120,6 +121,7 @@ internal Binding (EnumDeclarationSyntax enumDeclaration, INamedTypeSymbol symbol
 				bindingType = BindingType.SmartEnum;
 				enumMember = new EnumMember (
 					name: enumValueDeclaration.Identifier.ToFullString ().Trim (),
+		  index: (uint) index,
 					libraryName: libraryName,
 					libraryPath: libraryPath,
 					fieldData: enumValueSymbol.GetFieldData (),

src/rgen/Microsoft.Macios.Transformer/DataModel/EnumMember.Transformer.cs

@@ -40,12 +40,13 @@ public EnumMember (string name,
 	}
 
 	public EnumMember (string name,
+		uint index,
 		string libraryName,
 		string? libraryPath,
 		FieldData? fieldData,
-		SymbolAvailability symbolAvailability)
+		SymbolAvailability symbolAvailability) : this (StructState.Initialized, name)
 	{
-		Name = name;
+		Index = index;
 		SymbolAvailability = symbolAvailability;
 		FieldInfo = new (fieldData, libraryName, libraryPath);
 	}

tests/rgen/Microsoft.Macios.Generator.Tests/DataModel/BindingComparerTests.cs

@@ -196,6 +196,7 @@ public void CompareDifferentMembersLength ()
 			EnumMembers = [
 				new EnumMember (
 					name: "name",
+					index: 0,
 					libraryName: "Test",
 					libraryPath: "/path/to/library",
 					fieldData: new (),
@@ -218,6 +219,7 @@ public void CompareDifferentMembers ()
 			EnumMembers = [
 				new EnumMember (
 					name: "name",
+					index: 0,
 					libraryName: "Test",
 					libraryPath: "/path/to/library",
 					fieldData: new (),
@@ -234,6 +236,7 @@ public void CompareDifferentMembers ()
 			EnumMembers = [
 				new EnumMember (
 					name: "name2",
+					index: 0,
 					libraryName: "Test",
 					libraryPath: "/path/to/library",
 					fieldData: new (),

tests/rgen/Microsoft.Macios.Generator.Tests/DataModel/BindingEqualityComparerTests.cs

@@ -115,6 +115,7 @@ public void CompareDifferentMembersLength ()
 			EnumMembers = [
 				new EnumMember (
 					name: "name",
+					index: 0,
 					libraryName: "Test",
 					libraryPath: "/path/to/library",
 					fieldData: new (),
@@ -137,6 +138,7 @@ public void CompareDifferentMembers ()
 			EnumMembers = [
 				new EnumMember (
 					name: "name",
+					index: 0,
 					libraryName: "Test",
 					libraryPath: "/path/to/library",
 					fieldData: new (),
@@ -153,6 +155,7 @@ public void CompareDifferentMembers ()
 			EnumMembers = [
 				new EnumMember (
 					name: "name2",
+					index: 0,
 					libraryName: "Test",
 					libraryPath: "/path/to/library",
 					fieldData: new (),

tests/rgen/Microsoft.Macios.Generator.Tests/DataModel/BindingTests.cs

@@ -275,6 +275,7 @@ public void EnumIndexTest ()
 			EnumMembers = [
 				new (
 					name: "BuiltInMicrophone",
+					index: 0,
 					libraryName: "AVCaptureDeviceTypeBuiltInMicrophone",
 					libraryPath: null,
 					fieldData: new (presentSelector),