Revert "Fix LastContractPropertiesMap overriding collection property type when element type changes" (#10411)

Reverts #10319

This change is leading to breaks in the Search library. The original
behavior probably makes more sense. GAed property types cannot be
changed without introducing new property names via custom code.

Author: JoshLove-msft

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

@@ -538,17 +538,9 @@ protected internal override PropertyProvider[] BuildProperties()
                 // Targeted backcompat fix for the case where properties were previously generated as read-only collections
                 if (outputProperty.Type.IsReadWriteList || outputProperty.Type.IsReadWriteDictionary)
                 {
-                    // We compare Arguments by name (not just ElementType) to cover both list element types
-                    // and dictionary key/value types. This ensures we only override the collection wrapper
-                    // (e.g. IReadOnlyList<T> → IList<T>) and not when the element type itself has changed.
-                    // We use AreNamesEqual rather than Equals because the argument types may come from
-                    // different sources (TypeProvider vs compiled assembly) but represent the same logical type.
                     if (LastContractPropertiesMap.TryGetValue(outputProperty.Name,
                             out CSharpType? lastContractPropertyType) &&
-                        !outputProperty.Type.Equals(lastContractPropertyType) &&
-                        outputProperty.Type.Arguments.Count == lastContractPropertyType.Arguments.Count &&
-                        outputProperty.Type.Arguments.Zip(lastContractPropertyType.Arguments).All(
-                            pair => pair.First.AreNamesEqual(pair.Second)))
+                        !outputProperty.Type.Equals(lastContractPropertyType))
                     {
                         outputProperty.Type = lastContractPropertyType.ApplyInputSpecProperty(property);
                         CodeModelGenerator.Instance.Emitter.Info($"Changed property {Name}.{outputProperty.Name} type to {lastContractPropertyType} to match last contract.");

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

@@ -1062,51 +1062,6 @@ await MockHelpers.LoadMockGeneratorAsync(
             Assert.IsTrue(moreItemsProperty!.Type.Equals(new CSharpType(typeof(IReadOnlyDictionary<,>), typeof(string), elementEnumProvider.Type)));
         }
 
-        [Test]
-        public async Task BackCompat_CollectionPropertyTypeNotOverriddenWhenElementTypeChanges()
-        {
-            // Simulate the scenario where the element type of a collection property has changed
-            // (e.g., from Record<unknown>[] to BulkVMConfiguration[] via @typeChangedFrom).
-            // The last contract has IList<IDictionary<string, BinaryData>> but the new code model
-            // produces IList<NewElementModel>. The override should NOT apply because the element
-            // type has changed.
-            var newElementModel = InputFactory.Model(
-                "NewElementModel",
-                properties:
-                [
-                    InputFactory.Property("name", InputPrimitiveType.String)
-                ]);
-            var inputModel = InputFactory.Model(
-                "MockInputModel",
-                properties:
-                [
-                    InputFactory.Property("items", InputFactory.Array(newElementModel)),
-                    InputFactory.Property("moreItems", InputFactory.Dictionary(newElementModel))
-                ]);
-
-            await MockHelpers.LoadMockGeneratorAsync(
-                inputModelTypes: [inputModel, newElementModel],
-                lastContractCompilation: async () => await Helpers.GetCompilationFromDirectoryAsync());
-
-            var modelProvider = CodeModelGenerator.Instance.OutputLibrary.TypeProviders.SingleOrDefault(t => t.Name == "MockInputModel") as ModelProvider;
-            Assert.IsNotNull(modelProvider);
-
-            var newElementModelProvider = CodeModelGenerator.Instance.OutputLibrary.TypeProviders.SingleOrDefault(t => t.Name == "NewElementModel") as ModelProvider;
-            Assert.IsNotNull(newElementModelProvider);
-
-            // The items property should use the new element type (IList<NewElementModel>), not be
-            // overridden to the old type (IList<IDictionary<string, BinaryData>>) from last contract
-            var itemsProperty = modelProvider!.Properties.FirstOrDefault(p => p.Name == "Items");
-            Assert.IsNotNull(itemsProperty);
-            Assert.IsTrue(itemsProperty!.Type.Equals(new CSharpType(typeof(IList<>), newElementModelProvider!.Type)));
-
-            // The moreItems property should use the new element type (IDictionary<string, NewElementModel>), not be
-            // overridden to the old type (IDictionary<string, IDictionary<string, BinaryData>>) from last contract
-            var moreItemsProperty = modelProvider.Properties.FirstOrDefault(p => p.Name == "MoreItems");
-            Assert.IsNotNull(moreItemsProperty);
-            Assert.IsTrue(moreItemsProperty!.Type.Equals(new CSharpType(typeof(IDictionary<,>), typeof(string), newElementModelProvider.Type)));
-        }
-
         [Test]
         public async Task BackCompat_InternalTypesAreIgnored()
         {