JSON deserialization for positional record throws exception w/ Source Generator

[avdv]

Description

Following the instructions here: https://devblogs.microsoft.com/dotnet/try-the-new-system-text-json-source-generator/ I created a new project, installed the latest build for the System.Text.Json package:

1. dotnet new console
2. dotnet add package System.Text.Json --version 6.0.0-rc.1.21372.4

Code:

internal record Person(string FirstName, string LastName);

[JsonSourceGenerationOptions(
    PropertyNamingPolicy = JsonKnownNamingPolicy.CamelCase)]
[JsonSerializable(typeof(Person))]
internal partial class MyJsonContext : JsonSerializerContext
{
}

Person person = new(FirstName: "Jane", LastName: "Doe");
byte[] utf8Json = JsonSerializer.SerializeToUtf8Bytes(person, MyJsonContext.Default.Person);
person = JsonSerializer.Deserialize<Person>(utf8Json); // works
person = JsonSerializer.Deserialize<Person>(utf8Json, MyJsonContext.Default.Person); // fails

This works when using the reflection based deserialization.

But throws a NotSupportedException: "Deserialization of types without a parameterless constructor, a singular parameterized constructor, or a parameterized constructor annotated with 'JsonConstructorAttribute' is not supported." although the record only has a single parameterized constructor, AFAIK.

Configuration

.NET SDK (reflecting any global.json):
 Version:   5.0.202
 Commit:    db7cc87d51

Runtime Environment:
 OS Name:     nixos
 OS Version:  21.05.1486.2a96414d7e3
 OS Platform: Linux
 RID:         linux-x64
 Base Path:   /nix/store/9q8cavv72f5z71w6rddfqk82q2waa4s0-dotnet-sdk-5.0.202/sdk/5.0.202/

Host (useful for support):
  Version: 5.0.5
  Commit:  2f740adc14

.NET SDKs installed:
  5.0.202 [/nix/store/9q8cavv72f5z71w6rddfqk82q2waa4s0-dotnet-sdk-5.0.202/sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 5.0.5 [/nix/store/9q8cavv72f5z71w6rddfqk82q2waa4s0-dotnet-sdk-5.0.202/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 5.0.5 [/nix/store/9q8cavv72f5z71w6rddfqk82q2waa4s0-dotnet-sdk-5.0.202/shared/Microsoft.NETCore.App]

To install additional .NET runtimes or SDKs:
  https://aka.ms/dotnet-download

Regression?

no.

Other information

Unhandled exception. System.NotSupportedException: Deserialization of types without a parameterless constructor, a singular parameterized constructor, or a parameterized constructor annotated with 'JsonConstructorAttribute' is not supported. Type 'Test.Person'. Path: $ | LineNumber: 0 | BytePositionInLine: 1.
 ---> System.NotSupportedException: Deserialization of types without a parameterless constructor, a singular parameterized constructor, or a parameterized constructor annotated with 'JsonConstructorAttribute' is not supported. Type 'Test.Person'.
   --- End of inner exception stack trace ---
   at System.Text.Json.ThrowHelper.ThrowNotSupportedException(ReadStack& state, Utf8JsonReader& reader, NotSupportedException ex)
   at System.Text.Json.ThrowHelper.ThrowNotSupportedException_DeserializeNoConstructor(Type type, Utf8JsonReader& reader, ReadStack& state)
   at System.Text.Json.Serialization.Converters.ObjectDefaultConverter`1.OnTryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value)
   at System.Text.Json.Serialization.Converters.JsonMetadataServicesConverter`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.ReadCore[TValue](JsonConverter jsonConverter, Utf8JsonReader& reader, JsonSerializerOptions options, ReadStack& state)
   at System.Text.Json.JsonSerializer.ReadUsingMetadata[TValue](ReadOnlySpan`1 utf8Json, JsonTypeInfo jsonTypeInfo, Nullable`1 actualByteCount)
   at System.Text.Json.JsonSerializer.ReadUsingMetadata[TValue](ReadOnlySpan`1 json, JsonTypeInfo jsonTypeInfo)
   at System.Text.Json.JsonSerializer.Deserialize[TValue](String json, JsonTypeInfo`1 jsonTypeInfo)
   at sourcegen.Program.Main(String[] args) in /home/claudio/src/sourcegen/Program.cs:line 31

[ghost]

Tagging subscribers to this area: @eiriktsarpalis, @layomia
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Description

Following the instructions here: https://devblogs.microsoft.com/dotnet/try-the-new-system-text-json-source-generator/ I created a new project, installed the latest build for the System.Text.Json package:

1. dotnet new console
2. dotnet add package System.Text.Json --version 6.0.0-rc.1.21372.4

Code:

internal record Person(string FirstName, string LastName);

[JsonSourceGenerationOptions(
    PropertyNamingPolicy = JsonKnownNamingPolicy.CamelCase)]
[JsonSerializable(typeof(Person))]
internal partial class MyJsonContext : JsonSerializerContext
{
}

Person person = new(FirstName: "Jane", LastName: "Doe");
byte[] utf8Json = JsonSerializer.SerializeToUtf8Bytes(person, MyJsonContext.Default.Person);
person = JsonSerializer.Deserialize<Person>(utf8Json); // works
person = JsonSerializer.Deserialize<Person>(utf8Json, MyJsonContext.Default.Person); // fails

This works when using the reflection based deserialization.

But throws a NotSupportedException: "Deserialization of types without a parameterless constructor, a singular parameterized constructor, or a parameterized constructor annotated with 'JsonConstructorAttribute' is not supported." although the record only has a single parameterized constructor, AFAIK.

Configuration

.NET SDK (reflecting any global.json):
 Version:   5.0.202
 Commit:    db7cc87d51

Runtime Environment:
 OS Name:     nixos
 OS Version:  21.05.1486.2a96414d7e3
 OS Platform: Linux
 RID:         linux-x64
 Base Path:   /nix/store/9q8cavv72f5z71w6rddfqk82q2waa4s0-dotnet-sdk-5.0.202/sdk/5.0.202/

Host (useful for support):
  Version: 5.0.5
  Commit:  2f740adc14

.NET SDKs installed:
  5.0.202 [/nix/store/9q8cavv72f5z71w6rddfqk82q2waa4s0-dotnet-sdk-5.0.202/sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 5.0.5 [/nix/store/9q8cavv72f5z71w6rddfqk82q2waa4s0-dotnet-sdk-5.0.202/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 5.0.5 [/nix/store/9q8cavv72f5z71w6rddfqk82q2waa4s0-dotnet-sdk-5.0.202/shared/Microsoft.NETCore.App]

To install additional .NET runtimes or SDKs:
  https://aka.ms/dotnet-download

Regression?

no.

Other information

Unhandled exception. System.NotSupportedException: Deserialization of types without a parameterless constructor, a singular parameterized constructor, or a parameterized constructor annotated with 'JsonConstructorAttribute' is not supported. Type 'Test.Person'. Path: $ | LineNumber: 0 | BytePositionInLine: 1.
 ---> System.NotSupportedException: Deserialization of types without a parameterless constructor, a singular parameterized constructor, or a parameterized constructor annotated with 'JsonConstructorAttribute' is not supported. Type 'Test.Person'.
   --- End of inner exception stack trace ---
   at System.Text.Json.ThrowHelper.ThrowNotSupportedException(ReadStack& state, Utf8JsonReader& reader, NotSupportedException ex)
   at System.Text.Json.ThrowHelper.ThrowNotSupportedException_DeserializeNoConstructor(Type type, Utf8JsonReader& reader, ReadStack& state)
   at System.Text.Json.Serialization.Converters.ObjectDefaultConverter`1.OnTryRead(Utf8JsonReader& reader, Type typeToConvert, JsonSerializerOptions options, ReadStack& state, T& value)
   at System.Text.Json.Serialization.Converters.JsonMetadataServicesConverter`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.ReadCore[TValue](JsonConverter jsonConverter, Utf8JsonReader& reader, JsonSerializerOptions options, ReadStack& state)
   at System.Text.Json.JsonSerializer.ReadUsingMetadata[TValue](ReadOnlySpan`1 utf8Json, JsonTypeInfo jsonTypeInfo, Nullable`1 actualByteCount)
   at System.Text.Json.JsonSerializer.ReadUsingMetadata[TValue](ReadOnlySpan`1 json, JsonTypeInfo jsonTypeInfo)
   at System.Text.Json.JsonSerializer.Deserialize[TValue](String json, JsonTypeInfo`1 jsonTypeInfo)
   at sourcegen.Program.Main(String[] args) in /home/claudio/src/sourcegen/Program.cs:line 31

Author:	avdv
Assignees:	-
Labels:	area-System.Text.Json, untriaged
Milestone:	-

[layomia]

Thanks for the feedback! I'm currently working on a PR fixing this and will tag you once it's ready.