Json Source Generator no code generated for Deserialize?

[Alois-xx]

I was trying out source generators with .NET 7.0 and found a nice win of 20+% for the serialize case. Deserialize on the other hand did not really change, except for warmup.

When I set GenerationMode = JsonSourceGenerationMode.Serialization the code fails with an exception during deserialize.

System.InvalidOperationException: TypeInfoResolver 'SerializerTests.Serializers.MyJsonContext' did not provide property metadata for type 'SerializerTests.TypesToSerialize.BookShelf'.
   at System.Text.Json.ThrowHelper.ThrowInvalidOperationException_NoMetadataForTypeProperties(IJsonTypeInfoResolver resolver, Type type)
   at System.Text.Json.JsonSerializer.LookupProperty(Object obj, ReadOnlySpan`1 unescapedPropertyName, ReadStack& state, JsonSerializerOptions options, Boolean& useExtensionProperty, Boolean createExtensionProperty)
   at System.Text.Json.Serialization.Converters.ObjectDefaultConverter`1.OnTryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value)
   at System.Text.Json.Serialization.JsonConverter`1.TryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value)
   at System.Text.Json.Serialization.JsonConverter`1.ReadCore(Utf8JsonReader& reader, JsonSerializerOptions options, ReadStack& state)
   at System.Text.Json.JsonSerializer.ContinueDeserialize[TValue](ReadBufferState& bufferState, JsonReaderState& jsonReaderState, ReadStack& readStack, JsonTypeInfo jsonTypeInfo)
   at System.Text.Json.JsonSerializer.ReadFromStream[TValue](Stream utf8Json, JsonTypeInfo jsonTypeInfo)
   at SerializerTests.Serializers.SystemTextJsonSourceGen`1.Deserialize(Stream stream) in D:\Source\git\SerializerTests\Serializers\SystemTextJsonSourceGen.cs:line 75
   at SerializerTests.TestBase`2.TestDeserializeOnlyAndTouch(MemoryStream dataStream, Int32 nExpectedObjects, T& deserialized) in D:\Source\git\SerializerTests\TestBase.cs:line 247
   at SerializerTests.TestBase`2.<>c__DisplayClass39_0.<TestDeserialize>b__0() in D:\Source\git\SerializerTests\TestBase.cs:line 229
   at SerializerTests.TestBase`2.Test(Int32 n, Action acc, Boolean isSerialize) in D:\Source\git\SerializerTests\TestBase.cs:line 168
   at SerializerTests.TestBase`2.TestDeserialize(Int32 nTimes, Int32 nObjectsToCreate) in D:\Source\git\SerializerTests\TestBase.cs:line 226
   at SerializerTests.Test_O_N_Behavior.TestDeserialize(Int32[] nObjectsToDeSerialize, Int32 nRuns) in D:\Source\git\SerializerTests\Test_O_N_Behavior.cs:line 58
   at SerializerTests.Program.Deserialize() in D:\Source\git\SerializerTests\Program.cs:line 557
   at SerializerTests.Program.Run() in D:\Source\git\SerializerTests\Program.cs:line 505
   at SerializerTests.Program.Main(String[] args) in D:\Source\git\SerializerTests\Program.cs:line 404

Does this mean the mode JsonSourceGenerationMode.Serialization only generates code for the serialization logic, but not for deserialization? I this the reason why the default is to generate both? Is there some feature missing to not generate the metadata, but use pregenerated code for serialize and deserialize?
When I can have generated code why should I ever want to enable JsonSourceGenerationMode.Metadata, except to get some fallback when the generated code does not support some scenarios? Will there be a JsonSourceGenerationMode.Deserialization mode, or did I just call the wrong overload to use the pregenerated code?

    //
    // Summary:
    //     The generation mode for the System.Text.Json source generator.
    [Flags]
    public enum JsonSourceGenerationMode
    {
        //
        // Summary:
        //     When specified on System.Text.Json.Serialization.JsonSourceGenerationOptionsAttribute.GenerationMode,
        //     indicates that both type-metadata initialization logic and optimized serialization
        //     logic should be generated for all types. When specified on System.Text.Json.Serialization.JsonSerializableAttribute.GenerationMode,
        //     indicates that the setting on System.Text.Json.Serialization.JsonSourceGenerationOptionsAttribute.GenerationMode
        //     should be used.
        Default = 0,
        //
        // Summary:
        //     Instructs the JSON source generator to generate type-metadata initialization
        //     logic.
        Metadata = 1,
        //
        // Summary:
        //     Instructs the JSON source generator to generate optimized serialization logic.
        Serialization = 2
    }

`

[JsonSourceGenerationOptions(GenerationMode = JsonSourceGenerationMode.Default, IncludeFields = true)]
[JsonSerializable(typeof(BookShelf))]
[JsonSerializable(typeof(BookShelf1))]
[JsonSerializable(typeof(BookShelf2))]
[JsonSerializable(typeof(LargeBookShelf))]
internal partial class MyJsonContext : JsonSerializerContext
{
}

/// <summary>
/// Source Generators for .NET were added with .NET 7.0 which generate de/serialization code during compilation
/// </summary>
/// <typeparam name="T"></typeparam>
[SerializerType("https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json/source-generation See docu for Source Generators",
                SerializerTypes.Json | SerializerTypes.SupportsVersioning)]
class SystemTextJsonSourceGen<T> : TestBase<T, JsonSerializerOptions>
{
    public SystemTextJsonSourceGen(Func<int, T> testData, Action<T, int, int> touchAndVerify) : base(testData, touchAndVerify)
    {
    }

    [MethodImpl(MethodImplOptions.NoInlining)]
    protected override void Serialize(T obj, Stream stream)
    {
        // Use overload which uses precompiled serialization code
        string dat = JsonSerializer.Serialize(obj, MyJsonContext.Default.Options);

        using IMemoryOwner<byte> utf8_Owner = MemoryPool<byte>.Shared.Rent(dat.Length*2);

        // we still need to convert back to UTF8 or we will write UTF-16 with double size to disk
        int bytes = Encoding.UTF8.GetBytes(dat, utf8_Owner.Memory.Span);
        Span<byte> utf8Span = utf8_Owner.Memory.Span[..bytes];
                    
        stream.Write(utf8Span);
    }

    [MethodImpl(MethodImplOptions.NoInlining)]
    protected override T Deserialize(Stream stream)
    {
        // Currently we need to use the MetaData approach for deserialization. 
        // Precompiled Deserialization seems not to be supported yet? 

        if (typeof(T) == typeof(BookShelf))
        {
            return (T) (object) JsonSerializer.Deserialize(stream, MyJsonContext.Default.BookShelf);
        }
        else if (typeof(T) == typeof(BookShelf1))
        {
            return (T) JsonSerializer.Deserialize(stream, MyJsonContext.Default.BookShelf1.Type, MyJsonContext.Default);
        }
        else if (typeof(T) == typeof(BookShelf2))
        {
            return (T) JsonSerializer.Deserialize(stream, MyJsonContext.Default.BookShelf2.Type, MyJsonContext.Default);
        }
        else if (typeof(T) == typeof(LargeBookShelf))
        {
            return (T)JsonSerializer.Deserialize(stream, MyJsonContext.Default.LargeBookShelf.Type, MyJsonContext.Default);
        }

        throw new NotSupportedException($"No source generator for type {typeof(T).Name} declared.");

    }

`

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Issue Details

---

I was trying out source generators with .NET 7.0 and found a nice win of 20+% for the serialize case. Deserialize on the other hand did not really change, except for warmup.

When I set GenerationMode = JsonSourceGenerationMode.Serialization the code fails with an exception during deserialize.

System.InvalidOperationException: TypeInfoResolver 'SerializerTests.Serializers.MyJsonContext' did not provide property metadata for type 'SerializerTests.TypesToSerialize.BookShelf'.
   at System.Text.Json.ThrowHelper.ThrowInvalidOperationException_NoMetadataForTypeProperties(IJsonTypeInfoResolver resolver, Type type)
   at System.Text.Json.JsonSerializer.LookupProperty(Object obj, ReadOnlySpan`1 unescapedPropertyName, ReadStack& state, JsonSerializerOptions options, Boolean& useExtensionProperty, Boolean createExtensionProperty)
   at System.Text.Json.Serialization.Converters.ObjectDefaultConverter`1.OnTryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value)
   at System.Text.Json.Serialization.JsonConverter`1.TryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value)
   at System.Text.Json.Serialization.JsonConverter`1.ReadCore(Utf8JsonReader& reader, JsonSerializerOptions options, ReadStack& state)
   at System.Text.Json.JsonSerializer.ContinueDeserialize[TValue](ReadBufferState& bufferState, JsonReaderState& jsonReaderState, ReadStack& readStack, JsonTypeInfo jsonTypeInfo)
   at System.Text.Json.JsonSerializer.ReadFromStream[TValue](Stream utf8Json, JsonTypeInfo jsonTypeInfo)
   at SerializerTests.Serializers.SystemTextJsonSourceGen`1.Deserialize(Stream stream) in D:\Source\git\SerializerTests\Serializers\SystemTextJsonSourceGen.cs:line 75
   at SerializerTests.TestBase`2.TestDeserializeOnlyAndTouch(MemoryStream dataStream, Int32 nExpectedObjects, T& deserialized) in D:\Source\git\SerializerTests\TestBase.cs:line 247
   at SerializerTests.TestBase`2.<>c__DisplayClass39_0.<TestDeserialize>b__0() in D:\Source\git\SerializerTests\TestBase.cs:line 229
   at SerializerTests.TestBase`2.Test(Int32 n, Action acc, Boolean isSerialize) in D:\Source\git\SerializerTests\TestBase.cs:line 168
   at SerializerTests.TestBase`2.TestDeserialize(Int32 nTimes, Int32 nObjectsToCreate) in D:\Source\git\SerializerTests\TestBase.cs:line 226
   at SerializerTests.Test_O_N_Behavior.TestDeserialize(Int32[] nObjectsToDeSerialize, Int32 nRuns) in D:\Source\git\SerializerTests\Test_O_N_Behavior.cs:line 58
   at SerializerTests.Program.Deserialize() in D:\Source\git\SerializerTests\Program.cs:line 557
   at SerializerTests.Program.Run() in D:\Source\git\SerializerTests\Program.cs:line 505
   at SerializerTests.Program.Main(String[] args) in D:\Source\git\SerializerTests\Program.cs:line 404

Does this mean the mode JsonSourceGenerationMode.Serialization only generates code for the serialization logic, but not for deserialization? I this the reason why the default is to generate both? Is there some feature missing to not generate the metadata, but use pregenerated code for serialize and deserialize?
When I can have generated code why should I ever want to enable JsonSourceGenerationMode.Metadata, except to get some fallback when the generated code does not support some scenarios? Will there be a JsonSourceGenerationMode.Deserialization mode, or did I just call the wrong overload to use the pregenerated code?

    //
    // Summary:
    //     The generation mode for the System.Text.Json source generator.
    [Flags]
    public enum JsonSourceGenerationMode
    {
        //
        // Summary:
        //     When specified on System.Text.Json.Serialization.JsonSourceGenerationOptionsAttribute.GenerationMode,
        //     indicates that both type-metadata initialization logic and optimized serialization
        //     logic should be generated for all types. When specified on System.Text.Json.Serialization.JsonSerializableAttribute.GenerationMode,
        //     indicates that the setting on System.Text.Json.Serialization.JsonSourceGenerationOptionsAttribute.GenerationMode
        //     should be used.
        Default = 0,
        //
        // Summary:
        //     Instructs the JSON source generator to generate type-metadata initialization
        //     logic.
        Metadata = 1,
        //
        // Summary:
        //     Instructs the JSON source generator to generate optimized serialization logic.
        Serialization = 2
    }

`

[JsonSourceGenerationOptions(GenerationMode = JsonSourceGenerationMode.Default, IncludeFields = true)]
[JsonSerializable(typeof(BookShelf))]
[JsonSerializable(typeof(BookShelf1))]
[JsonSerializable(typeof(BookShelf2))]
[JsonSerializable(typeof(LargeBookShelf))]
internal partial class MyJsonContext : JsonSerializerContext
{
}

/// <summary>
/// Source Generators for .NET were added with .NET 7.0 which generate de/serialization code during compilation
/// </summary>
/// <typeparam name="T"></typeparam>
[SerializerType("https://learn.microsoft.com/en-us/dotnet/standard/serialization/system-text-json/source-generation See docu for Source Generators",
                SerializerTypes.Json | SerializerTypes.SupportsVersioning)]
class SystemTextJsonSourceGen<T> : TestBase<T, JsonSerializerOptions>
{
    public SystemTextJsonSourceGen(Func<int, T> testData, Action<T, int, int> touchAndVerify) : base(testData, touchAndVerify)
    {
    }

    [MethodImpl(MethodImplOptions.NoInlining)]
    protected override void Serialize(T obj, Stream stream)
    {
        // Use overload which uses precompiled serialization code
        string dat = JsonSerializer.Serialize(obj, MyJsonContext.Default.Options);

        using IMemoryOwner<byte> utf8_Owner = MemoryPool<byte>.Shared.Rent(dat.Length*2);

        // we still need to convert back to UTF8 or we will write UTF-16 with double size to disk
        int bytes = Encoding.UTF8.GetBytes(dat, utf8_Owner.Memory.Span);
        Span<byte> utf8Span = utf8_Owner.Memory.Span[..bytes];
                    
        stream.Write(utf8Span);
    }

    [MethodImpl(MethodImplOptions.NoInlining)]
    protected override T Deserialize(Stream stream)
    {
        // Currently we need to use the MetaData approach for deserialization. 
        // Precompiled Deserialization seems not to be supported yet? 

        if (typeof(T) == typeof(BookShelf))
        {
            return (T) (object) JsonSerializer.Deserialize(stream, MyJsonContext.Default.BookShelf);
        }
        else if (typeof(T) == typeof(BookShelf1))
        {
            return (T) JsonSerializer.Deserialize(stream, MyJsonContext.Default.BookShelf1.Type, MyJsonContext.Default);
        }
        else if (typeof(T) == typeof(BookShelf2))
        {
            return (T) JsonSerializer.Deserialize(stream, MyJsonContext.Default.BookShelf2.Type, MyJsonContext.Default);
        }
        else if (typeof(T) == typeof(LargeBookShelf))
        {
            return (T)JsonSerializer.Deserialize(stream, MyJsonContext.Default.LargeBookShelf.Type, MyJsonContext.Default);
        }

        throw new NotSupportedException($"No source generator for type {typeof(T).Name} declared.");

    }

`

Author:	Alois-xx
Assignees:	-
Labels:	area-System.Text.Json, tenet-performance
Milestone:	-

[eiriktsarpalis]

Fast-path deserialization has not been implemented yet, see #55043. If you need your source generator to support deserialization you should use the default JsonSourceGenerationMode in your configuration.