Add support for [Id] annotations on record primary constructor parameters

Co-authored-by: ReubenBond <203839+ReubenBond@users.noreply.github.com>

Author: Copilot

src/Orleans.CodeGenerator/FieldIdAssignmentHelper.cs

@@ -77,7 +77,8 @@ private bool ExtractFieldIdAnnotations()
                 }
                 else if (PropertyUtility.GetMatchingPrimaryConstructorParameter(prop, _constructorParameters) is { } prm)
                 {
-                    id = CodeGenerator.GetId(_libraryTypes, prop);
+                    // Check for [Id] attribute on the primary constructor parameter
+                    id = CodeGenerator.GetId(_libraryTypes, prm);
                     if (id.HasValue)
                     {
                         _symbols[member] = (id.Value, true);
@@ -108,7 +109,12 @@ private bool ExtractFieldIdAnnotations()
                         var constructorParameter = _constructorParameters.FirstOrDefault(x => x.Name.Equals(property.Name, StringComparison.OrdinalIgnoreCase));
                         if (constructorParameter is not null)
                         {
-                            id = (uint)_constructorParameters.IndexOf(constructorParameter);
+                            // Check for [Id] attribute on the constructor parameter
+                            id = CodeGenerator.GetId(_libraryTypes, constructorParameter);
+                            if (!id.HasValue)
+                            {
+                                id = (uint)_constructorParameters.IndexOf(constructorParameter);
+                            }
                             isConstructorParameter = true;
                         }
                     }

src/Orleans.Serialization.Abstractions/Annotations.cs

@@ -258,6 +258,7 @@ public GetCompletionSourceMethodNameAttribute(string methodName)
     [AttributeUsage(
         AttributeTargets.Field
         | AttributeTargets.Property
+        | AttributeTargets.Parameter
         | AttributeTargets.Class
         | AttributeTargets.Struct
         | AttributeTargets.Enum

test/Orleans.CodeGenerator.Tests/OrleansSourceGeneratorTests.cs

@@ -185,6 +185,33 @@ public record class DemoDataRecordClass([property: Id(0)] string Value);
 [GenerateSerializer]
 public record DemoDataRecord([property: Id(0)] string Value);");
 
+    /// <summary>
+    /// Tests serializer generation for records with [Id] attributes on primary constructor parameters.
+    /// This is the new, more concise syntax that avoids the need for [property: Id(0)].
+    /// Verifies that:
+    /// - [Id] on constructor parameters is properly detected and used
+    /// - Generated serializers correctly handle the property-parameter relationship
+    /// - Both simple records and records with additional properties work correctly
+    /// </summary>
+    [Fact]
+    public Task TestRecordsWithParameterIdAttributes() => AssertSuccessfulSourceGeneration(
+@"using Orleans;
+
+namespace TestProject;
+
+[GenerateSerializer]
+public record SimpleRecord([Id(0)] int Value, [Id(1)] string Name);
+
+[GenerateSerializer]
+public record RecordWithExtraProperty([Id(0)] int Id, [Id(1)] string Name)
+{
+    [Id(2)]
+    public string Description { get; init; }
+}
+
+[GenerateSerializer]
+public record struct RecordStructWithParameterId([Id(0)] string Value);");
+
     /// <summary>
     /// Tests serializer generation for generic types.
     /// Generic types require: