Use deterministic ordering for C# derived-model references

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

@@ -131,7 +131,7 @@ private IReadOnlyList<ModelProvider> BuildDerivedModels()
                 }
             }
 
-            return [.. derivedModels];
+            return [.. derivedModels.OrderBy(m => m.Name, StringComparer.Ordinal)];
         }
         internal override TypeProvider? BaseTypeProvider => _baseTypeProvider ??= BuildBaseTypeProvider();
         private TypeProvider? _baseTypeProvider;

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

@@ -87,7 +87,7 @@ private static IEnumerable<TestCaseData> GetBaseModels()
             yield return new TestCaseData(_baseModel, """
                                                       /// <summary>
                                                       /// pet description
-                                                      /// Please note this is the abstract base class. The derived classes available for instantiation are: <see cref="Sample.Models.Cat"/>, <see cref="Sample.Models.Dog"/>, and <see cref="Sample.Models.AnotherAnimal"/>.
+                                                      /// Please note this is the abstract base class. The derived classes available for instantiation are: <see cref="Sample.Models.AnotherAnimal"/>, <see cref="Sample.Models.Cat"/>, and <see cref="Sample.Models.Dog"/>.
                                                       /// </summary>
 
                                                       """);
@@ -120,8 +120,8 @@ public void BaseShouldBeAbstract(InputModelType inputModel, string expectedSumma
             Assert.AreEqual(expectedSummary, baseModel.XmlDocs.Summary!.ToDisplayString());
         }
 
-        [TestCase(true, "Please note this is the abstract base class. The derived classes available for instantiation are: <see cref=\"Sample.Models.Cat\"/>, <see cref=\"Sample.Models.Dog\"/>, and <see cref=\"Sample.Models.AnotherAnimal\"/>.")]
-        [TestCase(false, "Please note this is the base class. The derived classes available for instantiation are: <see cref=\"Sample.Models.Cat\"/>, <see cref=\"Sample.Models.Dog\"/>, and <see cref=\"Sample.Models.AnotherAnimal\"/>.")]
+        [TestCase(true, "Please note this is the abstract base class. The derived classes available for instantiation are: <see cref=\"Sample.Models.AnotherAnimal\"/>, <see cref=\"Sample.Models.Cat\"/>, and <see cref=\"Sample.Models.Dog\"/>.")]
+        [TestCase(false, "Please note this is the base class. The derived classes available for instantiation are: <see cref=\"Sample.Models.AnotherAnimal\"/>, <see cref=\"Sample.Models.Cat\"/>, and <see cref=\"Sample.Models.Dog\"/>.")]
         public void DiscriminatedBaseDescriptionReflectsAbstractness(bool isAbstract, string expectedDescription)
         {
             MockHelpers.LoadMockGenerator();

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

@@ -50,6 +50,32 @@ public void TestBuildDescription_SkipsDerivedClassesTextWhenNoPublicDerivedModel
             Assert.AreEqual("BaseModel description", provider!.Description.ToString());
         }
 
+        [TestCase(false)]
+        [TestCase(true)]
+        [SetCulture("en-US")]
+        public void DerivedModelsAreSortedAndDeduplicated(bool reverseInputOrder)
+        {
+            var cat = InputFactory.Model("Cat");
+            var zebra = InputFactory.Model("Zebra");
+            var antelope = InputFactory.Model("antelope", isExactName: true);
+            InputModelType[] subtypes = [zebra, cat];
+            InputModelType[] derivedModels = [antelope, cat];
+            if (reverseInputOrder)
+            {
+                Array.Reverse(subtypes);
+                Array.Reverse(derivedModels);
+            }
+
+            var inputModel = InputFactory.Model(
+                "Animal",
+                discriminatedModels: subtypes.ToDictionary(m => m.Name),
+                derivedModels: derivedModels);
+            var model = CodeModelGenerator.Instance.TypeFactory.CreateModel(inputModel);
+
+            Assert.IsNotNull(model);
+            Assert.AreEqual(new[] { "Cat", "Zebra", "antelope" }, model!.DerivedModels.Select(m => m.Name));
+        }
+
         [Test]
         public void TestBuildProperties_ValidateInheritHierarchyWithOverride()
         {

packages/http-client-csharp/generator/TestProjects/Local/Sample-TypeSpec/src/Generated/Models/Animal.Serialization.cs

@@ -14,7 +14,7 @@ namespace SampleTypeSpec
 {
     /// <summary>
     /// Base animal with discriminator
-    /// Please note this is the abstract base class. The derived classes available for instantiation are: <see cref="Pet"/> and <see cref="Dog"/>.
+    /// Please note this is the abstract base class. The derived classes available for instantiation are: <see cref="Dog"/> and <see cref="Pet"/>.
     /// </summary>
     [PersistableModelProxy(typeof(UnknownAnimal))]
     public abstract partial class Animal : IJsonModel<Animal>
@@ -150,10 +150,10 @@ internal static Animal DeserializeAnimal(JsonElement element, ModelReaderWriterO
             {
                 switch (discriminator.GetString())
                 {
-                    case "pet":
-                        return Pet.DeserializePet(element, options);
                     case "dog":
                         return Dog.DeserializeDog(element, options);
+                    case "pet":
+                        return Pet.DeserializePet(element, options);
                 }
             }
             return UnknownAnimal.DeserializeUnknownAnimal(element, options);

packages/http-client-csharp/generator/TestProjects/Local/Sample-TypeSpec/src/Generated/Models/Animal.cs

@@ -12,7 +12,7 @@ namespace SampleTypeSpec
 {
     /// <summary>
     /// Base animal with discriminator
-    /// Please note this is the abstract base class. The derived classes available for instantiation are: <see cref="Pet"/> and <see cref="Dog"/>.
+    /// Please note this is the abstract base class. The derived classes available for instantiation are: <see cref="Dog"/> and <see cref="Pet"/>.
     /// </summary>
     public abstract partial class Animal
     {

packages/http-client-csharp/generator/TestProjects/Local/Sample-TypeSpec/src/Generated/SampleTypeSpecModelFactory.cs

@@ -440,7 +440,7 @@ public static StreamingItem StreamingItem(string message = default)
 
         /// <summary>
         /// Base animal with discriminator
-        /// Please note this is the abstract base class. The derived classes available for instantiation are: <see cref="SampleTypeSpec.Pet"/> and <see cref="SampleTypeSpec.Dog"/>.
+        /// Please note this is the abstract base class. The derived classes available for instantiation are: <see cref="SampleTypeSpec.Dog"/> and <see cref="SampleTypeSpec.Pet"/>.
         /// </summary>
         /// <param name="kind"> The kind of animal. </param>
         /// <param name="name"> Name of the animal. </param>