[http-client-csharp]: Don't include custom required literal properties in public ctor (#4783)

This PR addresses an issue where required spec properties that were
literals and then customized to another literal type were being
incorrectly included in the public constructor.

fixes: https://github.com/microsoft/typespec/issues/4747

packages/http-client-csharp/generator/Microsoft.Generator.CSharp/src/Providers/CanonicalTypeProvider.cs

@@ -103,20 +103,10 @@ namespace Microsoft.Generator.CSharp.Providers
                 }
 
                 // handle customized enums - we need to pull the type information from the spec property
-                if (IsCustomizedEnumProperty(specProperty, customProperty.Type, out var specType))
-                {
-                    customProperty.Type = new CSharpType(
-                        customProperty.Type.Name,
-                        customProperty.Type.Namespace,
-                        customProperty.Type.IsValueType,
-                        customProperty.Type.IsNullable,
-                        customProperty.Type.DeclaringType,
-                        customProperty.Type.Arguments,
-                        customProperty.Type.IsPublic,
-                        customProperty.Type.IsStruct,
-                        customProperty.Type.BaseType,
-                        TypeFactory.CreatePrimitiveCSharpTypeCore(specType));
-                }
+                customProperty.Type = EnsureEnum(specProperty, customProperty.Type);
+
+                // ensure literal types are correctly represented in the custom property using the info from the spec property
+                customProperty.Type = EnsureLiteral(specProperty, customProperty.Type);
             }
 
             return [..generatedProperties, ..customProperties];
@@ -181,20 +171,10 @@ namespace Microsoft.Generator.CSharp.Providers
                 }
 
                 // handle customized enums - we need to pull the type information from the spec property
-                if (IsCustomizedEnumProperty(specProperty, customField.Type, out var specType))
-                {
-                    customField.Type = new CSharpType(
-                        customField.Type.Name,
-                        customField.Type.Namespace,
-                        customField.Type.IsValueType,
-                        customField.Type.IsNullable,
-                        customField.Type.DeclaringType,
-                        customField.Type.Arguments,
-                        customField.Type.IsPublic,
-                        customField.Type.IsStruct,
-                        customField.Type.BaseType,
-                        TypeFactory.CreatePrimitiveCSharpTypeCore(specType));
-                }
+                customField.Type = EnsureEnum(specProperty, customField.Type);
+
+                // ensure literal types are correctly represented in the custom field using the info from the spec property
+                customField.Type = EnsureLiteral(specProperty, customField.Type);
             }
 
             return [..generatedFields, ..customFields];
@@ -220,6 +200,35 @@ namespace Microsoft.Generator.CSharp.Providers
             return false;
         }
 
+        private static CSharpType EnsureLiteral(InputModelProperty? specProperty, CSharpType customType)
+        {
+            if (specProperty?.Type is InputLiteralType inputLiteral && (customType.IsFrameworkType || customType.IsEnum))
+            {
+                return CSharpType.FromLiteral(customType, inputLiteral.Value);
+            }
+
+            return customType;
+        }
+
+        private static CSharpType EnsureEnum(InputModelProperty? specProperty, CSharpType customType)
+        {
+            if (IsCustomizedEnumProperty(specProperty, customType, out var specType))
+            {
+                return new CSharpType(
+                    customType.Name,
+                    customType.Namespace,
+                    customType.IsValueType,
+                    customType.IsNullable,
+                    customType.DeclaringType,
+                    customType.Arguments,
+                    customType.IsPublic,
+                    customType.IsStruct,
+                    customType.BaseType,
+                    TypeFactory.CreatePrimitiveCSharpTypeCore(specType));
+            }
+            return customType;
+        }
+
         private static InputPrimitiveType? GetEnumValueType(InputType? type)
         {
             return type switch

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

@@ -500,5 +500,75 @@ namespace Microsoft.Generator.CSharp.Tests.Providers.ModelProviders
             Assert.IsTrue(ctors.Any(c => c.Signature.Modifiers.HasFlag(MethodSignatureModifiers.Public)));
             Assert.IsTrue(ctors.Any(c => c.Signature.Modifiers.HasFlag(MethodSignatureModifiers.Internal)));
         }
+
+        // Validates that if a required literal property is customized, then the default ctor
+        // does not include the custom property as a parameter.
+        [Test]
+        public async Task DoesNotIncludeReqCustomLiteralInDefaultCtor()
+        {
+            var enumType = InputFactory.Enum(
+                "originalEnum",
+                InputPrimitiveType.String,
+                values: [InputFactory.EnumMember.String("bar", "bar")]);
+            var plugin = await MockHelpers.LoadMockPluginAsync(
+                inputModelTypes: [
+                    InputFactory.Model(
+                        "mockInputModel",
+                        usage: InputModelTypeUsage.Input,
+                        properties:
+                        [
+                            InputFactory.Property("Prop1", InputFactory.Literal.Enum(enumType, "bar"), isRequired: true),
+                            InputFactory.Property("Prop2", InputPrimitiveType.String, isRequired: true),
+                        ])
+                    ],
+                compilation: async () => await Helpers.GetCompilationFromDirectoryAsync());
+            var csharpGen = new CSharpGen();
+
+            await csharpGen.ExecuteAsync();
+
+            var ctors = plugin.Object.OutputLibrary.TypeProviders.Single(t => t.Name == "MockInputModel").Constructors;
+            Assert.AreEqual(2, ctors.Count);
+
+            var publicCtor = ctors.FirstOrDefault(c => c.Signature.Modifiers.HasFlag(MethodSignatureModifiers.Public));
+            Assert.IsNotNull(publicCtor);
+
+            var ctorParams = publicCtor!.Signature.Parameters;
+
+            // should not have the custom required literal property
+            Assert.AreEqual(1, ctorParams.Count);
+            Assert.AreEqual("prop2", ctorParams[0].Name);
+        }
+
+        [Test]
+        public async Task DoesNotIncludeReqCustomFieldLiteralInDefaultCtor()
+        {
+            var plugin = await MockHelpers.LoadMockPluginAsync(
+                inputModelTypes: [
+                    InputFactory.Model(
+                        "mockInputModel",
+                        usage: InputModelTypeUsage.Input,
+                        properties:
+                        [
+                            InputFactory.Property("Prop1", InputFactory.Literal.String("bar"), isRequired: true),
+                            InputFactory.Property("Prop2", InputPrimitiveType.String, isRequired: true),
+                        ])
+                    ],
+                compilation: async () => await Helpers.GetCompilationFromDirectoryAsync());
+            var csharpGen = new CSharpGen();
+
+            await csharpGen.ExecuteAsync();
+
+            var ctors = plugin.Object.OutputLibrary.TypeProviders.Single(t => t.Name == "MockInputModel").Constructors;
+            Assert.AreEqual(2, ctors.Count);
+
+            var publicCtor = ctors.FirstOrDefault(c => c.Signature.Modifiers.HasFlag(MethodSignatureModifiers.Public));
+            Assert.IsNotNull(publicCtor);
+
+            var ctorParams = publicCtor!.Signature.Parameters;
+
+            // should not have the custom required literal property
+            Assert.AreEqual(1, ctorParams.Count);
+            Assert.AreEqual("prop2", ctorParams[0].Name);
+        }
     }
 }

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

@@ -0,0 +1,9 @@
+using Microsoft.Generator.CSharp.Customization;
+
+namespace Sample.Models;
+
+public partial class MockInputModel
+{
+    [CodeGenMember("Prop1")]
+    private string _prop1 = "bar";
+}

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

@@ -0,0 +1,14 @@
+using Microsoft.Generator.CSharp.Customization;
+
+namespace Sample.Models;
+
+public partial class MockInputModel
+{
+    [CodeGenMember("Prop1")]
+    public CustomEnum Prop1 { get; } = CustomEnum.Bar;
+}
+
+public enum CustomEnum
+{
+    Bar
+}