fix: respect custom property & field nullability

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/src/Utilities/CSharpTypeExtensions.cs

@@ -55,14 +55,9 @@ private static CSharpType EnsureNamespace(InputProperty? specProperty, CSharpTyp
                 // Use the TypeFactory to get the correct namespace for the type which respects any customizations that have
                 // been applied to the generated types.
                 var newType = CodeModelGenerator.Instance.TypeFactory.CreateCSharpType(inputType);
-                if (specProperty?.IsRequired == false && newType?.IsCollection == false)
-                {
-                    newType = newType.WithNullable(true);
-                }
-
                 if (newType != null)
                 {
-                    return newType;
+                    return type.IsNullable ? newType.WithNullable(true) : newType;
                 }
             }
 

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/test/Providers/ModelProviders/ModelCustomizationTests.cs

@@ -302,7 +302,7 @@ public async Task CanChangeListOfModelToReadOnlyListOfModel()
             var elementType = listProp.Type.ElementType;
             Assert.AreEqual("global::Sample.Models.Foo", elementType.ToString());
             Assert.AreEqual("Sample.Models", elementType.Namespace);
-            Assert.IsTrue(elementType.IsNullable);
+            Assert.IsFalse(elementType.IsNullable);
         }
 
         [Test]
@@ -336,9 +336,9 @@ public async Task CanChangeListOfEnumToReadOnlyListOfEnum()
             Assert.IsTrue(listProp.Type.IsList);
 
             var elementType = listProp.Type.ElementType;
-            Assert.AreEqual("global::Sample.Models.Foo?", elementType.ToString());
+            Assert.AreEqual("global::Sample.Models.Foo", elementType.ToString());
             Assert.AreEqual("Sample.Models", elementType.Namespace);
-            Assert.IsTrue(elementType.IsNullable);
+            Assert.IsFalse(elementType.IsNullable);
             Assert.IsFalse(elementType.IsStruct);
             Assert.IsFalse(elementType.IsLiteral);
         }
@@ -414,7 +414,7 @@ public async Task CanChangeDictionaryOfModelToReadOnlyDictionaryOfModel()
             var elementType = listProp.Type.ElementType;
             Assert.AreEqual("global::Sample.Models.Foo", elementType.ToString());
             Assert.AreEqual("Sample.Models", elementType.Namespace);
-            Assert.IsTrue(elementType.IsNullable);
+            Assert.IsFalse(elementType.IsNullable);
         }
 
         [Test]
@@ -483,7 +483,7 @@ public async Task CanChangeModelPropertyWithChangedNamespace()
 
             var modelProp = modelTypeProvider.CanonicalView.Properties[0];
             Assert.AreEqual("Prop1", modelProp.Name);
-            Assert.IsTrue(modelProp.Type.IsNullable);
+            Assert.IsFalse(modelProp.Type.IsNullable);
             Assert.IsFalse(modelProp.Body.HasSetter);
             Assert.AreEqual("global::Updated.Namespace.Models.Foo", modelProp.Type.ToString());
             Assert.AreEqual("Updated.Namespace.Models", modelProp.Type.Namespace);
@@ -626,6 +626,76 @@ public async Task CanChangeEnumToExtensibleEnum()
             Assert.IsTrue(enumProvider.DeclarationModifiers.HasFlag(TypeSignatureModifiers.Public | TypeSignatureModifiers.Partial | TypeSignatureModifiers.Struct | TypeSignatureModifiers.ReadOnly));
         }
 
+        [Test]
+        public async Task CanChangeEnumNullableTypeModelProperty()
+        {
+            var inputEnum = InputFactory.Int32Enum(
+               "Foo",
+               [("val1", 1), ("val2", 2), ("val3", 3)],
+               isExtensible: false
+           );
+            var props = new[]
+            {
+                InputFactory.Property("Prop1", inputEnum),
+            };
+
+            var inputModel = InputFactory.Model("mockInputModel", properties: props);
+
+            var mockGenerator = await MockHelpers.LoadMockGeneratorAsync(
+                inputModelTypes: [inputModel],
+                compilation: async () => await Helpers.GetCompilationFromDirectoryAsync());
+
+            var modelTypeProvider = mockGenerator.Object.OutputLibrary.TypeProviders.Single(t => t.Name == "MockInputModel");
+            AssertCommon(modelTypeProvider, "Sample.Models", "MockInputModel");
+
+            // the property should be added to the custom code view
+            Assert.AreEqual(1, modelTypeProvider.CustomCodeView!.Properties.Count);
+            // the canonical type should be changed
+            Assert.AreEqual(1, modelTypeProvider.CanonicalView!.Properties.Count);
+
+            var modelProp = modelTypeProvider.CanonicalView.Properties[0];
+            Assert.AreEqual("Prop1", modelProp.Name);
+            Assert.IsFalse(modelProp.Type.IsNullable);
+            Assert.IsFalse(modelProp.Body.HasSetter);
+            Assert.AreEqual("global::Sample.Models.Foo", modelProp.Type.ToString());
+            Assert.AreEqual("Sample.Models", modelProp.Type.Namespace);
+        }
+
+        [Test]
+        public async Task CanChangeEnumTypeModelPropertyToNullable()
+        {
+            var inputEnum = InputFactory.Int32Enum(
+               "Foo",
+               [("val1", 1), ("val2", 2), ("val3", 3)],
+               isExtensible: false
+           );
+            var props = new[]
+            {
+                InputFactory.Property("Prop1", inputEnum),
+            };
+
+            var inputModel = InputFactory.Model("mockInputModel", properties: props);
+
+            var mockGenerator = await MockHelpers.LoadMockGeneratorAsync(
+                inputModelTypes: [inputModel],
+                compilation: async () => await Helpers.GetCompilationFromDirectoryAsync());
+
+            var modelTypeProvider = mockGenerator.Object.OutputLibrary.TypeProviders.Single(t => t.Name == "MockInputModel");
+            AssertCommon(modelTypeProvider, "Sample.Models", "MockInputModel");
+
+            // the property should be added to the custom code view
+            Assert.AreEqual(1, modelTypeProvider.CustomCodeView!.Properties.Count);
+            // the canonical type should be changed
+            Assert.AreEqual(1, modelTypeProvider.CanonicalView!.Properties.Count);
+
+            var modelProp = modelTypeProvider.CanonicalView.Properties[0];
+            Assert.AreEqual("Prop1", modelProp.Name);
+            Assert.IsTrue(modelProp.Type.IsNullable);
+            Assert.IsFalse(modelProp.Body.HasSetter);
+            Assert.AreEqual("global::Sample.Models.Foo?", modelProp.Type.ToString());
+            Assert.AreEqual("Sample.Models", modelProp.Type.Namespace);
+        }
+
         [Test]
         public async Task CanChangeExtensibleEnumToEnum()
         {

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/test/Providers/ModelProviders/TestData/ModelCustomizationTests/CanChangeDictionaryOfModelToReadOnlyDictionaryOfModel/MockInputModel.cs

@@ -6,5 +6,5 @@ namespace Sample.Models;
 
 public partial class MockInputModel
 {
-    public readonly IReadOnlyDictionary<string, Foo> Prop1 { get; };
+    public readonly IReadOnlyDictionary<string, Foo> Prop1 { get; }
 }

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/test/Providers/ModelProviders/TestData/ModelCustomizationTests/CanChangeEnumNullableTypeModelProperty/MockInputModel.cs

@@ -0,0 +1,10 @@
+using System;
+using System.Collections.Generic;
+using SampleTypeSpec;
+
+namespace Sample.Models;
+
+public partial class MockInputModel
+{
+    public Foo Prop1 { get; };
+}

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/test/Providers/ModelProviders/TestData/ModelCustomizationTests/CanChangeEnumTypeModelPropertyToNullable/MockInputModel.cs

@@ -0,0 +1,10 @@
+using System;
+using System.Collections.Generic;
+using SampleTypeSpec;
+
+namespace Sample.Models;
+
+public partial class MockInputModel
+{
+    public Foo? Prop1 { get; };
+}

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/test/Providers/ModelProviders/TestData/ModelCustomizationTests/CanChangeListOfModelToReadOnlyListOfModel/MockInputModel.cs

@@ -6,5 +6,5 @@ namespace Sample.Models;
 
 public partial class MockInputModel
 {
-    public readonly IReadOnlyList<Foo> Prop1 { get; };
+    public readonly IReadOnlyList<Foo> Prop1 { get; }
 }

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/test/Providers/ModelProviders/TestData/ModelCustomizationTests/CanChangeModelPropertyWithChangedNamespace/MockInputModel.cs

@@ -6,5 +6,5 @@ namespace Sample.Models;
 
 public partial class MockInputModel
 {
-    public Foo Prop1 { get; };
+    public Foo Prop1 { get; }
 }