Make a number of improvements to the System.Text.Json source generator (

#81239)

* Ensure singleton JsonTypeInfo instances are preconfigured using JsonSerializerOptions.

* Fix indentation & whitespace issues in the source generator.

* Fix #76829.

* Fix nullability annotations in GetTypeInfo gen.

* Add clarifying comment.

* Add testing for types without metadata or fast-path generation.

src/libraries/System.Text.Json/gen/JsonSourceGenerator.Emitter.cs

@@ -26,7 +26,6 @@ private sealed partial class Emitter
  private const string DefaultOptionsStaticVarName = "s_defaultOptions";
  private const string DefaultContextBackingStaticVarName = "s_defaultContext";
  internal const string GetConverterFromFactoryMethodName = "GetConverterFromFactory";
- private const string MakeReadOnlyMethodName = "MakeReadOnly";
  private const string InfoVarName = "info";
  private const string PropertyInfoVarName = "propertyInfo";
  internal const string JsonContextVarName = "jsonContext";
@@ -152,49 +151,50 @@ private void AddSource(string fileName, string source, bool isRootContextDef = f
  string? @namespace = _currentContext.ContextType.Namespace;
  bool isInGlobalNamespace = @namespace == JsonConstants.GlobalNamespaceValue;
 
- StringBuilder sb = new(@"// <auto-generated/>
+ StringBuilder sb = new("""
+// <auto-generated/>
 
 #nullable enable annotations
 #nullable disable warnings
 
 // Suppress warnings about [Obsolete] member usage in generated code.
-#pragma warning disable CS0618");
+#pragma warning disable CS0612, CS0618
+
+
+""");
+ int indentation = 0;
 
  if (!isInGlobalNamespace)
  {
- sb.Append(@$"
-
-namespace {@namespace}
-{{");
+ sb.AppendLine($$"""
+namespace {{@namespace}}
+{
+""");
+ indentation++;
  }
 
  for (int i = 0; i < declarationCount - 1; i++)
  {
- string declarationSource = $@"
-{declarationList[declarationCount - 1 - i]}
-{{";
- sb.Append($@"
-{IndentSource(declarationSource, numIndentations: i + 1)}
-");
+ string declarationSource = $$"""
+{{declarationList[declarationCount - 1 - i]}}
+{
+""";
+ sb.AppendLine(IndentSource(declarationSource, numIndentations: indentation++));
  }
 
  // Add the core implementation for the derived context class.
- string partialContextImplementation = $@"
-{generatedCodeAttributeSource}{declarationList[0]}{(interfaceImplementation is null ? "" : ": " + interfaceImplementation)}
-{{
- {IndentSource(source, Math.Max(1, declarationCount - 1))}
-}}";
- sb.AppendLine(IndentSource(partialContextImplementation, numIndentations: declarationCount));
-
- // Match curly brace for each containing type.
- for (int i = 0; i < declarationCount - 1; i++)
- {
- sb.AppendLine(IndentSource("}", numIndentations: declarationCount + i + 1));
- }
+ string partialContextImplementation = $$"""
+{{generatedCodeAttributeSource}}{{declarationList[0]}}{{(interfaceImplementation is null ? "" : ": " + interfaceImplementation)}}
+{
+{{IndentSource(source, 1)}}
+}
+""";
+ sb.AppendLine(IndentSource(partialContextImplementation, numIndentations: indentation--));
 
- if (!isInGlobalNamespace)
+ // Match curly braces for each containing type/namespace.
+ for (; indentation >= 0; indentation--)
  {
- sb.AppendLine("}");
+ sb.AppendLine(IndentSource("}", numIndentations: indentation));
  }
 
  _sourceGenerationContext.AddSource(fileName, SourceText.From(sb.ToString(), Encoding.UTF8));
@@ -1146,24 +1146,20 @@ private static string GenerateForType(TypeGenerationSpec typeMetadata, string me
  string typeInfoPropertyTypeRef = $"{JsonTypeInfoTypeRef}<{typeCompilableName}>";
 
  return @$"private {typeInfoPropertyTypeRef}? _{typeFriendlyName};
+
 /// <summary>
 /// Defines the source generated JSON serialization contract metadata for a given type.
 /// </summary>
 public {typeInfoPropertyTypeRef} {typeFriendlyName}
 {{
- get => _{typeFriendlyName} ??= {typeMetadata.CreateTypeInfoMethodName}({OptionsInstanceVariableName}, makeReadOnly: true);
+ get => _{typeFriendlyName} ??= ({typeInfoPropertyTypeRef}){OptionsInstanceVariableName}.GetTypeInfo(typeof({typeCompilableName}));
 }}
 
-private {typeInfoPropertyTypeRef} {typeMetadata.CreateTypeInfoMethodName}({JsonSerializerOptionsTypeRef} {OptionsLocalVariableName}, bool makeReadOnly)
+private {typeInfoPropertyTypeRef} {typeMetadata.CreateTypeInfoMethodName}({JsonSerializerOptionsTypeRef} {OptionsLocalVariableName})
 {{
  {typeInfoPropertyTypeRef}? {JsonTypeInfoReturnValueLocalVariableName} = null;
  {WrapWithCheckForCustomConverter(metadataInitSource, typeCompilableName)}
 
- if (makeReadOnly)
- {{
- {JsonTypeInfoReturnValueLocalVariableName}.{MakeReadOnlyMethodName}();
- }}
-
  return {JsonTypeInfoReturnValueLocalVariableName};
 }}
 {additionalSource}";
@@ -1324,13 +1320,14 @@ private string GetGetTypeInfoImplementation()
 
  sb.Append(
 @$"/// <inheritdoc/>
-public override {JsonTypeInfoTypeRef} GetTypeInfo({TypeTypeRef} type)
+public override {JsonTypeInfoTypeRef}? GetTypeInfo({TypeTypeRef} type)
 {{");
-
- HashSet<TypeGenerationSpec> types = new(_currentContext.TypesWithMetadataGenerated);
-
- // TODO (https:/dotnet/runtime/issues/52218): Make this Dictionary-lookup-based if root-serializable type count > 64.
- foreach (TypeGenerationSpec metadata in types)
+ // This method body grows linearly over the number of generated types.
+ // In line with https:/dotnet/runtime/issues/77897 we should
+ // eventually replace this method with a direct call to Options.GetTypeInfo().
+ // We can't do this currently because Options.GetTypeInfo throws whereas
+ // this GetTypeInfo returns null for unsupported types, so we need new API to support it.
+ foreach (TypeGenerationSpec metadata in _currentContext.TypesWithMetadataGenerated)
  {
  if (metadata.ClassType != ClassType.TypeUnsupportedBySourceGen)
  {
@@ -1344,22 +1341,21 @@ private string GetGetTypeInfoImplementation()
  }
 
  sb.AppendLine(@"
- return null!;
+ return null;
 }");
 
  // Explicit IJsonTypeInfoResolver implementation
  sb.AppendLine();
  sb.Append(@$"{JsonTypeInfoTypeRef}? {JsonTypeInfoResolverTypeRef}.GetTypeInfo({TypeTypeRef} type, {JsonSerializerOptionsTypeRef} {OptionsLocalVariableName})
 {{");
- // TODO (https:/dotnet/runtime/issues/52218): Make this Dictionary-lookup-based if root-serializable type count > 64.
- foreach (TypeGenerationSpec metadata in types)
+ foreach (TypeGenerationSpec metadata in _currentContext.TypesWithMetadataGenerated)
  {
  if (metadata.ClassType != ClassType.TypeUnsupportedBySourceGen)
  {
  sb.Append($@"
  if (type == typeof({metadata.TypeRef}))
  {{
- return {metadata.CreateTypeInfoMethodName}({OptionsLocalVariableName}, makeReadOnly: false);
+ return {metadata.CreateTypeInfoMethodName}({OptionsLocalVariableName});
  }}
 ");
  }
@@ -1393,8 +1389,13 @@ private string GetPropertyNameInitialization()
 
  private static string IndentSource(string source, int numIndentations)
  {
- Debug.Assert(numIndentations >= 1);
- return source.Replace(Environment.NewLine, $"{Environment.NewLine}{new string(' ', 4 * numIndentations)}"); // 4 spaces per indentation.
+ if (numIndentations == 0)
+ {
+ return source;
+ }
+
+ string indentation = new string(' ', 4 * numIndentations); // 4 spaces per indentation.
+ return indentation + source.Replace(Environment.NewLine, Environment.NewLine + indentation);
  }
 
  private static string GetNumberHandlingAsStr(JsonNumberHandling? numberHandling) =>

src/libraries/System.Text.Json/src/Resources/Strings.resx

@@ -617,9 +617,6 @@
  <data name="FSharpDiscriminatedUnionsNotSupported" xml:space="preserve">
  <value>F# discriminated union serialization is not supported. Consider authoring a custom converter for the type.</value>
  </data>
- <data name="NoMetadataForTypeCtorParams" xml:space="preserve">
- <value>TypeInfoResolver '{0}' did not provide constructor parameter metadata for type '{1}'.</value>
- </data>
  <data name="Polymorphism_BaseConverterDoesNotSupportMetadata" xml:space="preserve">
  <value>The converter for polymorphic type '{0}' does not support metadata writes or reads.</value>
  </data>

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerContext.cs

@@ -15,7 +15,7 @@ public abstract partial class JsonSerializerContext : IJsonTypeInfoResolver
 
  /// <summary>
  /// Gets the run time specified options of the context. If no options were passed
- /// when instanciating the context, then a new instance is bound and returned.
+ /// when instantiating the context, then a new instance is bound and returned.
  /// </summary>
  /// <remarks>
  /// The options instance cannot be mutated once it is bound to the context instance.

src/libraries/System.Text.Json/src/System/Text/Json/Serialization/Metadata/SourceGenJsonTypeInfoOfT.cs

@@ -107,11 +107,6 @@ internal override JsonParameterInfoValues[] GetParameterInfoValues()
  JsonParameterInfoValues[] array;
  if (CtorParamInitFunc == null || (array = CtorParamInitFunc()) == null)
  {
- if (SerializeHandler == null)
- {
- ThrowHelper.ThrowInvalidOperationException_NoMetadataForTypeCtorParams(Options.TypeInfoResolver, Type);
- }
-
  array = Array.Empty<JsonParameterInfoValues>();
  MetadataSerializationNotSupported = true;
  }
@@ -144,11 +139,6 @@ internal override void LateAddProperties()
  return;
  }
 
- if (SerializeHandler == null)
- {
- ThrowHelper.ThrowInvalidOperationException_NoMetadataForTypeProperties(Options.TypeInfoResolver, Type);
- }
-
  MetadataSerializationNotSupported = true;
  return;
  }

src/libraries/System.Text.Json/src/System/Text/Json/ThrowHelper.Serialization.cs

@@ -745,12 +745,6 @@ public static void ThrowInvalidOperationException_NoMetadataForTypeProperties(IJ
  throw GetInvalidOperationException_NoMetadataForTypeProperties(resolver, type);
  }
 
- [DoesNotReturn]
- public static void ThrowInvalidOperationException_NoMetadataForTypeCtorParams(IJsonTypeInfoResolver? resolver, Type type)
- {
- throw new InvalidOperationException(SR.Format(SR.NoMetadataForTypeCtorParams, resolver?.GetType().FullName ?? "<null>", type));
- }
-
  [DoesNotReturn]
  public static void ThrowMissingMemberException_MissingFSharpCoreMember(string missingFsharpCoreMember)
  {

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Tests/SerializationContextTests.cs

@@ -2,6 +2,7 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 
 using System.Text.Json.Serialization;
+using System.Text.Json.Serialization.Metadata;
 using System.Reflection;
 using Xunit;
 
@@ -208,6 +209,18 @@ public override void EnsureFastPathGeneratedAsExpected()
  Assert.Null(SerializationContext.Default.PolymorphicClass.SerializeHandler);
  }
 
+ [Fact]
+ public void TypeWithoutMetadataOrFastPathHandler_SerializationThrowsInvalidOperationException()
+ {
+ JsonTypeInfo<ClassWithCustomConverterProperty> typeInfo = SerializationContext.Default.ClassWithCustomConverterProperty;
+ Assert.Null(typeInfo.SerializeHandler);
+ Assert.Empty(typeInfo.Properties);
+
+ var value = new ClassWithCustomConverterProperty();
+ Assert.Throws<InvalidOperationException>(() => JsonSerializer.Serialize(value, typeInfo));
+ Assert.Throws<InvalidOperationException>(() => JsonSerializer.Deserialize("""{"Property":42}""", typeInfo));
+ }
+
  [Fact]
  public override void RoundTripLocation()
  {

src/libraries/System.Text.Json/tests/System.Text.Json.SourceGeneration.Unit.Tests/JsonSourceGeneratorTests.cs

@@ -735,6 +735,9 @@ public class ClassWithObsolete
  {
  [Obsolete(""This is a test"")]
  public bool Test { get; set; }
+
+ [Obsolete]
+ public bool Test2 { get; set; }
  }
 }
 ";