Do not use ref for patch property in structs (microsoft#8568)

fixes: microsoft#8567

Author: jorgerangel-msft

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/src/Providers/ScmModelProvider.cs

@@ -168,9 +168,11 @@ protected override ConstructorProvider[] BuildConstructors()
             }
 
             var experimentalAttribute = new AttributeStatement(typeof(ExperimentalAttribute), [Literal(ScmEvaluationTypeDiagnosticId)]);
-
+            FieldModifiers modifiers = DeclarationModifiers.HasFlag(TypeSignatureModifiers.Struct)
+                ? FieldModifiers.Private | FieldModifiers.ReadOnly
+                : FieldModifiers.Private;
             return new FieldProvider(
-                modifiers: FieldModifiers.Private,
+                modifiers: modifiers,
                 type: _jsonPatchFieldType,
                 description: null,
                 name: JsonPatchFieldName,
@@ -185,13 +187,14 @@ protected override ConstructorProvider[] BuildConstructors()
                 return null;
             }
 
+            bool isRef = !DeclarationModifiers.HasFlag(TypeSignatureModifiers.Struct);
             return new PropertyProvider(
                 description: null,
                 modifiers: MethodSignatureModifiers.Public,
                 type: _jsonPatchFieldType,
                 name: JsonPatchPropertyName,
-                isRef: true,
-                body: new ExpressionPropertyBody(new VariableExpression(JsonPatchField.Type, JsonPatchField.Declaration, IsRef: true)),
+                isRef: isRef,
+                body: new ExpressionPropertyBody(new VariableExpression(JsonPatchField.Type, JsonPatchField.Declaration, IsRef: isRef)),
                 attributes:
                 [
                     new AttributeStatement(typeof(EditorBrowsableAttribute), FrameworkEnumValue(EditorBrowsableState.Never)),

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/test/Providers/ScmModelProvider/ScmModelProviderTests.cs

@@ -3,6 +3,7 @@
 
 using System.Collections.Generic;
 using System.Linq;
+using System.Threading.Tasks;
 using Microsoft.TypeSpec.Generator.Input;
 using Microsoft.TypeSpec.Generator.Primitives;
 using Microsoft.TypeSpec.Generator.Tests.Common;
@@ -299,5 +300,47 @@ public void TestDynamicDerivedModel()
 
             Assert.AreEqual(Helpers.GetExpectedFromFile(), file.Content);
         }
+
+        [Test]
+        public void TestStructDynamicModel()
+        {
+            var catModel = InputFactory.Model("cat", isDynamicModel: true, modelAsStruct: true, properties:
+            [
+                InputFactory.Property("meows", InputPrimitiveType.Boolean, isRequired: true)
+            ]);
+
+            MockHelpers.LoadMockGenerator(inputModels: () => [catModel]);
+            var model = ScmCodeModelGenerator.Instance.TypeFactory.CreateModel(catModel) as ClientModel.Providers.ScmModelProvider;
+
+            Assert.IsNotNull(model);
+            Assert.IsTrue(model!.HasDynamicModelSupport);
+
+            var writer = new TypeProviderWriter(model);
+            var file = writer.Write();
+
+            Assert.AreEqual(Helpers.GetExpectedFromFile(), file.Content);
+        }
+
+        [Test]
+        public async Task TestCustomStructDynamicModel()
+        {
+            var catModel = InputFactory.Model("cat", isDynamicModel: true, properties:
+            [
+                InputFactory.Property("meows", InputPrimitiveType.Boolean, isRequired: true)
+            ]);
+
+            await MockHelpers.LoadMockGeneratorAsync(
+                compilation: async () => await Helpers.GetCompilationFromDirectoryAsync(),
+                inputModels: () => [catModel]);
+            var model = ScmCodeModelGenerator.Instance.TypeFactory.CreateModel(catModel) as ClientModel.Providers.ScmModelProvider;
+
+            Assert.IsNotNull(model);
+            Assert.IsTrue(model!.HasDynamicModelSupport);
+
+            var writer = new TypeProviderWriter(model);
+            var file = writer.Write();
+
+            Assert.AreEqual(Helpers.GetExpectedFromFile(), file.Content);
+        }
     }
 }

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/test/Providers/ScmModelProvider/TestData/ScmModelProviderTests/TestCustomStructDynamicModel.cs

@@ -0,0 +1,35 @@
+// <auto-generated/>
+
+#nullable disable
+
+using System.ClientModel.Primitives;
+using System.ComponentModel;
+using System.Diagnostics.CodeAnalysis;
+
+namespace Sample.Models
+{
+    internal readonly partial struct Cat
+    {
+        [global::System.Diagnostics.CodeAnalysis.ExperimentalAttribute("SCME0001")]
+        private readonly global::System.ClientModel.Primitives.JsonPatch _patch;
+
+        public Cat(bool meows)
+        {
+            Meows = meows;
+        }
+
+#pragma warning disable SCME0001 // Type is for evaluation purposes only and is subject to change or removal in future updates.
+        internal Cat(bool meows, in global::System.ClientModel.Primitives.JsonPatch patch)
+        {
+            Meows = meows;
+            _patch = patch;
+        }
+#pragma warning restore SCME0001 // Type is for evaluation purposes only and is subject to change or removal in future updates.
+
+        [global::System.ComponentModel.EditorBrowsableAttribute(global::System.ComponentModel.EditorBrowsableState.Never)]
+        [global::System.Diagnostics.CodeAnalysis.ExperimentalAttribute("SCME0001")]
+        public global::System.ClientModel.Primitives.JsonPatch Patch => _patch;
+
+        public bool Meows { get; }
+    }
+}

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/test/Providers/ScmModelProvider/TestData/ScmModelProviderTests/TestCustomStructDynamicModel/Cat.cs

@@ -0,0 +1,11 @@
+using System.ClientModel.Primitives;
+using System.ComponentModel;
+using System.Diagnostics.CodeAnalysis;
+
+namespace Sample.Models
+{
+    [CodeGenType("Cat")]
+    public partial readonly struct Cat
+    {
+    }
+}

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/test/Providers/ScmModelProvider/TestData/ScmModelProviderTests/TestStructDynamicModel.cs

@@ -0,0 +1,35 @@
+// <auto-generated/>
+
+#nullable disable
+
+using System.ClientModel.Primitives;
+using System.ComponentModel;
+using System.Diagnostics.CodeAnalysis;
+
+namespace Sample.Models
+{
+    public readonly partial struct Cat
+    {
+        [global::System.Diagnostics.CodeAnalysis.ExperimentalAttribute("SCME0001")]
+        private readonly global::System.ClientModel.Primitives.JsonPatch _patch;
+
+        public Cat(bool meows)
+        {
+            Meows = meows;
+        }
+
+#pragma warning disable SCME0001 // Type is for evaluation purposes only and is subject to change or removal in future updates.
+        internal Cat(bool meows, in global::System.ClientModel.Primitives.JsonPatch patch)
+        {
+            Meows = meows;
+            _patch = patch;
+        }
+#pragma warning restore SCME0001 // Type is for evaluation purposes only and is subject to change or removal in future updates.
+
+        [global::System.ComponentModel.EditorBrowsableAttribute(global::System.ComponentModel.EditorBrowsableState.Never)]
+        [global::System.Diagnostics.CodeAnalysis.ExperimentalAttribute("SCME0001")]
+        public global::System.ClientModel.Primitives.JsonPatch Patch => _patch;
+
+        public bool Meows { get; }
+    }
+}