Preserve internal C# helper types during trimming

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

@@ -17,7 +17,7 @@
 
 namespace Microsoft.TypeSpec.Generator.ClientModel.Providers
 {
-    public class BinaryContentHelperDefinition : TypeProvider
+    public class BinaryContentHelperDefinition : InternalHelperProvider
     {
         private const string _fromEnumerableName = "FromEnumerable";
         private const string _fromDictionaryName = "FromDictionary";
@@ -30,9 +30,6 @@ public class BinaryContentHelperDefinition : TypeProvider
 
         protected override string BuildName() => "BinaryContentHelper";
 
-        protected override TypeSignatureModifiers BuildDeclarationModifiers()
-            => TypeSignatureModifiers.Internal | TypeSignatureModifiers.Static | TypeSignatureModifiers.Partial | TypeSignatureModifiers.Class;
-
         protected override string BuildRelativeFilePath() => Path.Combine("src", "Generated", "Internal", $"{Name}.cs");
 
         protected override MethodProvider[] BuildMethods()

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

@@ -12,7 +12,7 @@
 
 namespace Microsoft.TypeSpec.Generator.ClientModel.Providers
 {
-    internal class CancellationTokenExtensionsDefinition : TypeProvider
+    internal class CancellationTokenExtensionsDefinition : InternalHelperProvider
     {
         private ParameterProvider _cancellationTokenParam;
 
@@ -21,11 +21,6 @@ public CancellationTokenExtensionsDefinition()
             _cancellationTokenParam = new ParameterProvider("cancellationToken", FormattableStringHelpers.Empty, typeof(CancellationToken));
         }
 
-        protected override TypeSignatureModifiers BuildDeclarationModifiers()
-        {
-            return TypeSignatureModifiers.Internal | TypeSignatureModifiers.Static;
-        }
-
         protected override string BuildRelativeFilePath() => Path.Combine("src", "Generated", "Internal", $"{Name}.cs");
 
         protected override string BuildName() => "CancellationTokenExtensions";

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

@@ -13,7 +13,7 @@
 
 namespace Microsoft.TypeSpec.Generator.ClientModel.Providers
 {
-    internal class ClientPipelineExtensionsDefinition : TypeProvider
+    internal class ClientPipelineExtensionsDefinition : InternalHelperProvider
     {
         private ParameterProvider _pipelineParam;
         private ParameterProvider _messageParam;
@@ -32,11 +32,6 @@ public ClientPipelineExtensionsDefinition()
             _options = _requestOptionsParam.ToApi<HttpRequestOptionsApi>();
         }
 
-        protected override TypeSignatureModifiers BuildDeclarationModifiers()
-        {
-            return TypeSignatureModifiers.Internal | TypeSignatureModifiers.Static;
-        }
-
         protected override string BuildRelativeFilePath() => Path.Combine("src", "Generated", "Internal", $"{Name}.cs");
 
         protected override string BuildName() => "ClientPipelineExtensions";

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

@@ -15,7 +15,7 @@
 
 namespace Microsoft.TypeSpec.Generator.ClientModel.Providers
 {
-    internal sealed class ClientUriBuilderDefinition : TypeProvider
+    internal sealed class ClientUriBuilderDefinition : InternalHelperProvider
     {
         private const string ToUriMethodName = "ToUri";
         private const string ResetMethodName = "Reset";
@@ -63,10 +63,7 @@ public ClientUriBuilderDefinition()
             _pathLengthField = new(FieldModifiers.Private, typeof(int), "_pathLength", this);
         }
 
-        protected override TypeSignatureModifiers BuildDeclarationModifiers()
-        {
-            return TypeSignatureModifiers.Internal;
-        }
+        protected override TypeSignatureModifiers BuildDeclarationModifiers() => TypeSignatureModifiers.Internal;
 
         protected override string BuildRelativeFilePath() => Path.Combine("src", "Generated", "Internal", $"{Name}.cs");
 

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

@@ -12,7 +12,7 @@
 
 namespace Microsoft.TypeSpec.Generator.ClientModel.Providers
 {
-    internal class ErrorResultDefinition : TypeProvider
+    internal class ErrorResultDefinition : InternalHelperProvider
     {
         private class ErrorResultTemplate<T> { }
 

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

@@ -27,7 +27,7 @@
 #pragma warning disable SCME0004 // FileBinaryContent is evaluation-only.
 namespace Microsoft.TypeSpec.Generator.ClientModel.Providers
 {
-    public sealed partial class ModelSerializationExtensionsDefinition : TypeProvider
+    public sealed partial class ModelSerializationExtensionsDefinition : InternalHelperProvider
     {
         public const string WireOptionsFieldName = "WireOptions";
         public const string JsonDocumentOptionsFieldName = "JsonDocumentOptions";
@@ -96,11 +96,6 @@ public ModelSerializationExtensionsDefinition()
                 enclosingType: this);
         }
 
-        protected override TypeSignatureModifiers BuildDeclarationModifiers()
-        {
-            return TypeSignatureModifiers.Internal | TypeSignatureModifiers.Static;
-        }
-
         internal FieldProvider WireOptionsField { get; }
         private readonly FieldProvider _jsonDocumentOptionsField;
 

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

@@ -21,7 +21,7 @@
 
 namespace Microsoft.TypeSpec.Generator.ClientModel.Providers
 {
-    public class MultiPartFormDataBinaryContentDefinition : TypeProvider
+    public class MultiPartFormDataBinaryContentDefinition : InternalHelperProvider
     {
         private readonly ScopedApi<MultipartFormDataContent> _multipartContentExpression;
         private readonly FieldProvider _multipartContentField;
@@ -77,7 +77,8 @@ public MultiPartFormDataBinaryContentDefinition()
 
         protected override string BuildName() => $"MultiPartFormData{_requestContentType.Name}";
 
-        protected override TypeSignatureModifiers BuildDeclarationModifiers() => TypeSignatureModifiers.Class | TypeSignatureModifiers.Internal;
+        protected override TypeSignatureModifiers BuildDeclarationModifiers()
+            => TypeSignatureModifiers.Internal | TypeSignatureModifiers.Class;
 
         protected override CSharpType BuildBaseType() => _requestContentType;
 

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

@@ -14,7 +14,7 @@
 
 namespace Microsoft.TypeSpec.Generator.ClientModel.Providers
 {
-    internal class MultipartFormDataHelperDefinition : TypeProvider
+    internal class MultipartFormDataHelperDefinition : InternalHelperProvider
     {
         private const string _fromEnumerableName = "FromEnumerable";
         private const string _fromDictionaryName = "FromDictionary";
@@ -24,9 +24,6 @@ internal class MultipartFormDataHelperDefinition : TypeProvider
 
         protected override string BuildName() => "MultipartFormDataHelper";
 
-        protected override TypeSignatureModifiers BuildDeclarationModifiers()
-            => TypeSignatureModifiers.Internal | TypeSignatureModifiers.Static | TypeSignatureModifiers.Partial | TypeSignatureModifiers.Class;
-
         protected override string BuildRelativeFilePath() => Path.Combine("src", "Generated", "Internal", $"{Name}.cs");
 
         protected override MethodProvider[] BuildMethods()

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

@@ -15,7 +15,7 @@
 
 namespace Microsoft.TypeSpec.Generator.ClientModel.Providers
 {
-    internal class PipelineRequestHeadersExtensionsDefinition : TypeProvider
+    internal class PipelineRequestHeadersExtensionsDefinition : InternalHelperProvider
     {
         private const string _setDelimited = "SetDelimited";
         private const string _addWithPrefix = "Add";
@@ -25,11 +25,6 @@ public PipelineRequestHeadersExtensionsDefinition()
             _pipelineRequestHeadersParam = new ParameterProvider("headers", FormattableStringHelpers.Empty, typeof(PipelineRequestHeaders));
         }
         private readonly CSharpType _t = typeof(IEnumerable<>).GetGenericArguments()[0];
-        protected override TypeSignatureModifiers BuildDeclarationModifiers()
-        {
-            return TypeSignatureModifiers.Internal | TypeSignatureModifiers.Static;
-        }
-
         protected override string BuildRelativeFilePath() => Path.Combine("src", "Generated", "Internal", $"{Name}.cs");
 
         protected override string BuildName() => "PipelineRequestHeadersExtensions";

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

@@ -16,7 +16,7 @@
 
 namespace Microsoft.TypeSpec.Generator.ClientModel.Providers
 {
-    internal sealed class TypeFormattersDefinition : TypeProvider
+    internal sealed class TypeFormattersDefinition : InternalHelperProvider
     {
         private readonly ValueExpression _invariantCultureExpression = new MemberExpression(typeof(CultureInfo), nameof(CultureInfo.InvariantCulture));
         private const string ToStringMethodName = "ToString";
@@ -33,11 +33,6 @@ internal TypeFormattersDefinition()
             _defaultNumberFormatField = new(FieldModifiers.Public | FieldModifiers.Const, typeof(string), "DefaultNumberFormat", this, initializationValue: Literal("G"));
         }
 
-        protected override TypeSignatureModifiers BuildDeclarationModifiers()
-        {
-            return TypeSignatureModifiers.Internal | TypeSignatureModifiers.Static;
-        }
-
         protected override string BuildRelativeFilePath() => Path.Combine("src", "Generated", "Internal", $"{Name}.cs");
 
         protected override string BuildName() => "TypeFormatters";

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/src/Providers/Utf8JsonBinaryContentDefinition.cs

@@ -16,7 +16,7 @@
 
 namespace Microsoft.TypeSpec.Generator.ClientModel.Providers
 {
-    public class Utf8JsonBinaryContentDefinition : TypeProvider
+    public class Utf8JsonBinaryContentDefinition : InternalHelperProvider
     {
         private const string _jsonWriterName = "JsonWriter";
 

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator.ClientModel/src/ScmCodeModelGenerator.cs

@@ -24,8 +24,9 @@ public class ScmCodeModelGenerator : CodeModelGenerator
 
         public override ScmTypeFactory TypeFactory { get; }
 
-        internal ModelSerializationExtensionsDefinition ModelSerializationExtensionsDefinition { get; } =
-            new ModelSerializationExtensionsDefinition();
+        internal ModelSerializationExtensionsDefinition ModelSerializationExtensionsDefinition
+            => _modelSerializationExtensionsDefinition ??= new ModelSerializationExtensionsDefinition();
+        private ModelSerializationExtensionsDefinition? _modelSerializationExtensionsDefinition;
 
         internal SerializationFormatDefinition SerializationFormatDefinition { get; } =
             new SerializationFormatDefinition();
@@ -50,6 +51,7 @@ protected override void Configure()
             AddMetadataReference(MetadataReference.CreateFromFile(typeof(BinaryData).Assembly.Location));
             AddMetadataReference(MetadataReference.CreateFromFile(typeof(JsonSerializer).Assembly.Location));
             AddTypeToKeep(ModelReaderWriterContextDefinition.s_name, isRoot: false);
+            AddTypeToKeep(SerializationFormatDefinition, isRoot: false);
         }
 
         public override async Task WriteAdditionalFiles(string outputPath)

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/src/PostProcessing/PostProcessor.cs

@@ -91,8 +91,7 @@ private async Task<TypeSymbols> GetTypeSymbolsAsync(Compilation compilation,
                         // we do not add the model factory and additionalNonRootTypeSymbols to the declared symbol list
                         // so that it will never be included in any process of internalization or removal
                         if (SymbolEqualityComparer.Default.Equals(symbol, _modelFactorySymbol)
-                            || _additionalNonRootTypeNames.Contains(symbol.Name)
-                            || _additionalNonRootTypeNames.Contains(symbol.GetFullyQualifiedName()))
+                            || IsAdditionalNonRootType(symbol))
                         {
                             continue;
                         }
@@ -110,6 +109,24 @@ private async Task<TypeSymbols> GetTypeSymbolsAsync(Compilation compilation,
                     kv => kv.Value.ToHashSet<INamedTypeSymbol>(SymbolEqualityComparer.Default)));
         }
 
+        private bool IsAdditionalNonRootType(INamedTypeSymbol symbol)
+        {
+            if (_additionalNonRootTypeNames.Contains(symbol.Name))
+            {
+                return true;
+            }
+
+            var fullyQualifiedName = symbol.GetFullyQualifiedName();
+            if (_additionalNonRootTypeNames.Contains(fullyQualifiedName))
+            {
+                return true;
+            }
+
+            var genericArityIndex = fullyQualifiedName.IndexOf('`');
+            return genericArityIndex > 0
+                && _additionalNonRootTypeNames.Contains(fullyQualifiedName[..genericArityIndex]);
+        }
+
         protected virtual bool ShouldIncludeDocument(Document document) =>
             !GeneratedCodeWorkspace.IsGeneratedTestDocument(document);
 

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

@@ -15,7 +15,7 @@
 
 namespace Microsoft.TypeSpec.Generator.Providers
 {
-    internal class ArgumentDefinition : TypeProvider
+    internal class ArgumentDefinition : InternalHelperProvider
     {
         private class Template<T> { }
 
@@ -34,11 +34,6 @@ public ArgumentDefinition()
             _nullableT = _t.WithNullable(true);
         }
 
-        protected override TypeSignatureModifiers BuildDeclarationModifiers()
-        {
-            return TypeSignatureModifiers.Internal | TypeSignatureModifiers.Static;
-        }
-
         private MethodSignature GetSignature(
             string name,
             IReadOnlyList<ParameterProvider> parameters,

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

@@ -13,7 +13,7 @@
 
 namespace Microsoft.TypeSpec.Generator.Providers
 {
-    internal sealed class ChangeTrackingDictionaryDefinition : TypeProvider
+    internal sealed class ChangeTrackingDictionaryDefinition : InternalHelperProvider
     {
         private class ChangeTrackingDictionaryTemplate<TKey, TValue> { }
         private readonly CSharpType _tKey = typeof(ChangeTrackingDictionaryTemplate<,>).GetGenericArguments()[0];
@@ -48,10 +48,7 @@ public ChangeTrackingDictionaryDefinition()
 
         protected override WhereExpression BuildWhereClause() => Where.NotNull(_tKey);
 
-        protected override TypeSignatureModifiers BuildDeclarationModifiers()
-        {
-            return TypeSignatureModifiers.Internal;
-        }
+        protected override TypeSignatureModifiers BuildDeclarationModifiers() => TypeSignatureModifiers.Internal;
 
         protected override string BuildRelativeFilePath() => Path.Combine("src", "Generated", "Internal", $"{Name}.cs");
 

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

@@ -13,7 +13,7 @@
 
 namespace Microsoft.TypeSpec.Generator.Providers
 {
-    internal sealed class ChangeTrackingListDefinition : TypeProvider
+    internal sealed class ChangeTrackingListDefinition : InternalHelperProvider
     {
         private class ChangeTrackingListTemplate<T> { }
 
@@ -46,10 +46,7 @@ public ChangeTrackingListDefinition()
             EnsureList = new(This.Invoke(_ensureListSignature));
         }
 
-        protected override TypeSignatureModifiers BuildDeclarationModifiers()
-        {
-            return TypeSignatureModifiers.Internal;
-        }
+        protected override TypeSignatureModifiers BuildDeclarationModifiers() => TypeSignatureModifiers.Internal;
 
         protected override string BuildRelativeFilePath() => Path.Combine("src", "Generated", "Internal", $"{Name}.cs");
 

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

@@ -0,0 +1,22 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+using Microsoft.TypeSpec.Generator.Input;
+using Microsoft.TypeSpec.Generator.Primitives;
+
+namespace Microsoft.TypeSpec.Generator.Providers
+{
+    /// <summary>
+    /// A base provider for generator-owned internal helper types that must not be removed during post-processing.
+    /// </summary>
+    public abstract class InternalHelperProvider : TypeProvider
+    {
+        protected InternalHelperProvider(InputType? inputType = default) : base(inputType)
+        {
+            CodeModelGenerator.Instance.AddTypeToKeep(this, isRoot: false);
+        }
+
+        protected override TypeSignatureModifiers BuildDeclarationModifiers()
+            => TypeSignatureModifiers.Internal | TypeSignatureModifiers.Static;
+    }
+}

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

@@ -11,7 +11,7 @@
 
 namespace Microsoft.TypeSpec.Generator.Providers
 {
-    public class OptionalDefinition : TypeProvider
+    public class OptionalDefinition : InternalHelperProvider
     {
         private class ListTemplate<T> { }
 
@@ -29,11 +29,6 @@ public OptionalDefinition()
             _tValue = _genericChangeTrackingDictionary.Arguments[1];
         }
 
-        protected override TypeSignatureModifiers BuildDeclarationModifiers()
-        {
-            return TypeSignatureModifiers.Internal | TypeSignatureModifiers.Static;
-        }
-
         protected override string BuildRelativeFilePath() => Path.Combine("src", "Generated", "Internal", $"{Name}.cs");
 
         protected override string BuildName() => "Optional";

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

@@ -17,9 +17,13 @@ namespace Microsoft.TypeSpec.Generator
 {
     public class TypeFactory
     {
-        private ChangeTrackingListDefinition ChangeTrackingListProvider { get; } = new();
+        private ChangeTrackingListDefinition ChangeTrackingListProvider
+            => _changeTrackingListProvider ??= new();
+        private ChangeTrackingListDefinition? _changeTrackingListProvider;
 
-        private ChangeTrackingDictionaryDefinition ChangeTrackingDictionaryProvider { get; } = new();
+        private ChangeTrackingDictionaryDefinition ChangeTrackingDictionaryProvider
+            => _changeTrackingDictionaryProvider ??= new();
+        private ChangeTrackingDictionaryDefinition? _changeTrackingDictionaryProvider;
 
         private Dictionary<InputModelType, ModelProvider?> InputTypeToModelProvider { get; } = [];