Merge branch 'main' of https://github.com/microsoft/typespec into sramsey/csharp-server-union-failure

Author: sophia-ramsey

.chronus/changes/add-python-duration-seconds-milliseconds-encode-2026-6-10-9-3-37.md

@@ -7,6 +7,8 @@
 using System.Linq;
 using Microsoft.TypeSpec.Generator.ClientModel.Providers;
 using Microsoft.TypeSpec.Generator.Input;
+using Microsoft.TypeSpec.Generator.Primitives;
+using Microsoft.TypeSpec.Generator.Providers;
 using Microsoft.TypeSpec.Generator.Tests.Common;
 using NUnit.Framework;
 
@@ -144,6 +146,53 @@ public void TestCreateSerializations_ReturnsBothMrwAndMultipart_WhenJsonAndMpfdU
                 "Expected a multipart serialization provider for a model with MultipartFormData usage.");
         }
 
+        // ScmTypeFactory overrides CreateModelCore to return ScmModelProvider. External-type
+        // handling lives in the (non-overridable) base TypeFactory.CreateModel, so it must still
+        // apply here. This guards against regressing the fix by re-introducing external handling
+        // into CreateModelCore only, which would silently drop the discriminator for the Scm path.
+        [Test]
+        public void ExternalBaseModel_MapsToSystemObjectModelProvider_AndForwardsDiscriminator_ThroughScmTypeFactory()
+        {
+            var baseModel = InputFactory.Model(
+                "Animal",
+                properties:
+                [
+                    InputFactory.Property("kind", InputPrimitiveType.String, isRequired: true, isDiscriminator: true),
+                    InputFactory.Property("name", InputPrimitiveType.String, isRequired: true),
+                ],
+                external: new InputExternalTypeMetadata("System.Exception", null, null));
+            var derivedModel = InputFactory.Model(
+                "Pet",
+                baseModel: baseModel,
+                discriminatedKind: "pet",
+                properties:
+                [
+                    InputFactory.Property("kind", InputPrimitiveType.String, isRequired: true, isDiscriminator: true),
+                    InputFactory.Property("trained", InputPrimitiveType.Boolean, isRequired: true),
+                ]);
+
+            MockHelpers.LoadMockGenerator(inputModels: () => [baseModel, derivedModel]);
+
+            // The external base maps to a SystemObjectModelProvider even though ScmTypeFactory
+            // overrides CreateModelCore.
+            var baseProvider = ScmCodeModelGenerator.Instance.TypeFactory.CreateModel(baseModel);
+            Assert.IsInstanceOf<SystemObjectModelProvider>(baseProvider);
+
+            // The derived model is a regular ScmModelProvider whose base is the SystemObjectModelProvider.
+            var derivedProvider = ScmCodeModelGenerator.Instance.TypeFactory.CreateModel(derivedModel) as ModelProvider;
+            Assert.IsNotNull(derivedProvider);
+            Assert.IsInstanceOf<ScmModelProvider>(derivedProvider);
+            Assert.IsInstanceOf<SystemObjectModelProvider>(derivedProvider!.BaseModelProvider);
+
+            // Some constructor forwards the discriminator literal to the external base.
+            var forwardsDiscriminator = derivedProvider.Constructors.Any(
+                c => c.Signature.Initializer is { IsBase: true } init &&
+                     init.Arguments.Any(a => a.ToDisplayString() == "\"pet\""));
+            Assert.IsTrue(
+                forwardsDiscriminator,
+                "Expected a base constructor call forwarding the discriminator value \"pet\" to the external base.");
+        }
+
         private static InputModelProperty FilePartProperty(string name)
             => InputFactory.Property(
                 name,

.chronus/changes/add-python-multiple-services-tests-2026-6-10-8-56-11.md

@@ -100,12 +100,12 @@ internal set
         public IReadOnlyList<string> SharedSourceDirectories => _sharedSourceDirectories;
 
         /// <summary>
-        /// The list of <see cref="TypeProvider"/> instances that define custom-code attributes. These attribute
+        /// The list of <see cref="CustomCodeAttributeDefinition"/> instances that define custom-code attributes. These attribute
         /// definitions are generated into the SDK project and are made available to the compiler while it compiles
         /// custom code. Derived generators can contribute additional providers via
-        /// <see cref="AddCustomCodeAttributeProvider(TypeProvider)"/>.
+        /// <see cref="AddCustomCodeAttributeProvider(CustomCodeAttributeDefinition)"/>.
         /// </summary>
-        internal List<TypeProvider> CustomCodeAttributeProviders { get; } =
+        internal List<CustomCodeAttributeDefinition> CustomCodeAttributeProviders { get; } =
         [
             new CodeGenTypeAttributeDefinition(),
             new CodeGenMemberAttributeDefinition(),
@@ -171,8 +171,8 @@ public virtual void AddSharedSourceDirectory(string sharedSourceDirectory)
         /// generator-specific attribute definitions. The provider's attribute definition is generated into
         /// the SDK project and made available to the compiler while it compiles custom code.
         /// </summary>
-        /// <param name="provider">The <see cref="TypeProvider"/> that defines the custom-code attribute.</param>
-        protected void AddCustomCodeAttributeProvider(TypeProvider provider)
+        /// <param name="provider">The <see cref="CustomCodeAttributeDefinition"/> that defines the custom-code attribute.</param>
+        protected void AddCustomCodeAttributeProvider(CustomCodeAttributeDefinition provider)
         {
             CustomCodeAttributeProviders.Add(provider);
         }