[RGen] Ensure that if a parameter name is a keyword that '@' is used as a prefix.

src/rgen/Microsoft.Macios.Bindings.Analyzer/Microsoft.Macios.Bindings.Analyzer.csproj

@@ -112,6 +112,9 @@
         <Compile Include="../Microsoft.Macios.Generator/Extensions/Delegates.cs" >
             <Link>Generator/Extensions/Delegates.cs</Link>
         </Compile>
+        <Compile Include="../Microsoft.Macios.Generator/Extensions/ParameterSymbolExtensions.cs" >
+            <Link>Generator/Extensions/ParameterSymbolExtensions.cs</Link>
+        </Compile>
         <Compile Include="../Microsoft.Macios.Generator/Extensions/SpecialTypeExtensions.cs" >
             <Link>Generator/Extensions/SpecialTypeExtensions.cs</Link>
         </Compile>

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

@@ -18,7 +18,7 @@ readonly partial struct DelegateParameter {
 	public static bool TryCreate (IParameterSymbol symbol,
 		[NotNullWhen (true)] out DelegateParameter? parameter)
 	{
-		parameter = new (symbol.Ordinal, new (symbol.Type), symbol.Name) {
+		parameter = new (symbol.Ordinal, new (symbol.Type), symbol.GetSafeName ()) {
 			ForcedType = symbol.GetForceTypeData (),
 			IsOptional = symbol.IsOptional,
 			IsParams = symbol.IsParams,

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

@@ -38,7 +38,7 @@ public bool NeedsNullCheck {
 	public static bool TryCreate (IParameterSymbol symbol, ParameterSyntax declaration, RootContext context,
 		[NotNullWhen (true)] out Parameter? parameter)
 	{
-		parameter = new (symbol.Ordinal, new (symbol.Type, context.Compilation), symbol.Name) {
+		parameter = new (symbol.Ordinal, new (symbol.Type, context.Compilation), symbol.GetSafeName ()) {
 			BindAs = symbol.GetBindFromData (),
 			ForcedType = symbol.GetForceTypeData (),
 			IsOptional = symbol.IsOptional,

src/rgen/Microsoft.Macios.Generator/Extensions/ParameterSymbolExtensions.cs

@@ -0,0 +1,29 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+
+namespace Microsoft.Macios.Generator.Extensions;
+
+public static class ParameterSymbolExtensions {
+
+	/// <summary>
+	/// Gets the safe name of the parameter symbol, prefixing with "@" if it's a C# keyword.
+	/// </summary>
+	/// <param name="symbol">The parameter symbol.</param>
+	/// <returns>The safe name of the parameter, suitable for use in generated C# code. 
+	/// For example, if the parameter name is "event", this method returns "@event". 
+	/// Otherwise, it returns the original parameter name.</returns>
+	public static string GetSafeName (this IParameterSymbol symbol)
+	{
+		// In C#, the @ symbol is used as an escape character to allow reserved keywords (like event) to be used as
+		// identifiers. However, when working with Roslyn's IParameterSymbol, the Name property returns the identifier
+		// without the @ prefix because the @ is only required in the source code to escape the keyword.
+		// Internally, the compiler treats the name as the unescaped version.
+		string parameterName = SyntaxFacts.GetKeywordKind (symbol.Name) != SyntaxKind.None
+			? "@" + symbol.Name
+			: symbol.Name;
+		return parameterName;
+	}
+}

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

@@ -3,6 +3,7 @@
 
 using System.Diagnostics.CodeAnalysis;
 using Microsoft.CodeAnalysis;
+using Microsoft.Macios.Generator.Extensions;
 using Microsoft.Macios.Transformer.Attributes;
 
 namespace Microsoft.Macios.Generator.DataModel;
@@ -17,7 +18,7 @@ readonly partial struct DelegateParameter {
 	public static bool TryCreate (IParameterSymbol symbol,
 		[NotNullWhen (true)] out DelegateParameter? parameter)
 	{
-		parameter = new (symbol.Ordinal, new (symbol.Type), symbol.Name) {
+		parameter = new (symbol.Ordinal, new (symbol.Type), symbol.GetSafeName ()) {
 			IsOptional = symbol.IsOptional,
 			IsParams = symbol.IsParams,
 			IsThis = symbol.IsThis,

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

@@ -27,7 +27,7 @@ public static bool TryCreate (IParameterSymbol symbol, ParameterSyntax declarati
 		// retrieve the parameter attributes because those might affect the parameter type, for example, the 
 		// NullAllowed attribute can change the parameter type to be nullable.
 		var parameterAttrs = symbol.GetAttributeData ();
-		parameter = new (symbol.Ordinal, new (symbol.Type, parameterAttrs), symbol.Name) {
+		parameter = new (symbol.Ordinal, new (symbol.Type, parameterAttrs), symbol.GetSafeName ()) {
 			IsOptional = symbol.IsOptional,
 			IsParams = symbol.IsParams,
 			IsThis = symbol.IsThis,

src/rgen/Microsoft.Macios.Transformer/Microsoft.Macios.Transformer.csproj

@@ -80,6 +80,9 @@
         <Compile Include="../Microsoft.Macios.Generator/Extensions/FieldSymbolExtensions.cs">
             <Link>Extensions/FieldSymbolExtensions.cs</Link>
         </Compile>
+        <Compile Include="../Microsoft.Macios.Generator/Extensions/ParameterSymbolExtensions.cs">
+            <Link>Extensions/ParameterSymbolExtensions.cs</Link>
+        </Compile>
         <Compile Include="../Microsoft.Macios.Generator/Extensions/ParameterSyntaxExtensions.cs">
             <Link>Extensions/ParameterSyntaxExtensions.cs</Link>
         </Compile>

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

@@ -523,6 +523,65 @@ public void MyMethod ([BlockCallback] Callback cb) {}
 					]
 				)
 			];
+
+			const string customDelegateKeywordParam = @"
+using System;
+
+namespace NS {
+	public class MyClass {
+		public delegate int? Callback(string @event, string? middleName, params string[] surname);
+
+		public void MyMethod (Callback cb) {}
+	}
+}
+";
+
+			yield return [
+				customDelegateKeywordParam,
+				new Method (
+					type: "NS.MyClass",
+					name: "MyMethod",
+					returnType: ReturnTypeForVoid (),
+					symbolAvailability: new (),
+					exportMethodData: new (),
+					attributes: [],
+					modifiers: [
+						SyntaxFactory.Token (SyntaxKind.PublicKeyword),
+					],
+					parameters: [
+						new (
+							position: 0,
+							type: ReturnTypeForDelegate (
+								"NS.MyClass.Callback",
+								delegateInfo: new (
+									name: "Invoke",
+									returnType: ReturnTypeForInt (isNullable: true),
+									parameters: [
+										new (
+											position: 0,
+											type: ReturnTypeForString (),
+											name: "@event"
+										),
+										new (
+											position: 1,
+											type: ReturnTypeForString (isNullable: true),
+											name: "middleName"
+										),
+										new (
+											position: 2,
+											type: ReturnTypeForArray ("string", isBlittable: false),
+											name: "surname"
+										) {
+											IsParams = true,
+										},
+									]
+								)
+							),
+							name: "cb"
+						)
+					]
+				)
+			];
 		}
 
 		IEnumerator IEnumerable.GetEnumerator () => GetEnumerator ();

tests/rgen/Microsoft.Macios.Generator.Tests/DataModel/MethodTests/FromDeclarationTests.cs

@@ -161,6 +161,34 @@ public class MyClass {
 				)
 			];
 
+			const string singleParameterKeywordNameMethod = @"
+using System;
+
+namespace NS {
+	public class MyClass {
+		public string MyMethod (string @event) => $""{@event}_test"";
+	}
+}
+";
+
+			yield return [
+				singleParameterKeywordNameMethod,
+				new Method (
+					type: "NS.MyClass",
+					name: "MyMethod",
+					returnType: ReturnTypeForString (),
+					symbolAvailability: new (),
+					exportMethodData: new (),
+					attributes: [],
+					modifiers: [
+						SyntaxFactory.Token (SyntaxKind.PublicKeyword),
+					],
+					parameters: [
+						new (position: 0, type: ReturnTypeForString (), name: "@event"),
+					]
+				)
+			];
+
 			const string singleArrayParameterMethod = @"
 using System;