SupportNonNullableReferenceTypes not working for nested record types

[michael-wolfenden]

Using Swashbuckle.AspNetCore 6.5.0

Given the following:

async Task Main()
{
    var builder = WebApplication.CreateBuilder();
    builder.Services.AddEndpointsApiExplorer();
    builder.Services.AddSwaggerGen(options =>
    {
        options.SupportNonNullableReferenceTypes();
    });
    
    var app = builder.Build();
    app.UseSwagger();
    app.UseSwaggerUI();

    app.MapPost("/requestWithNestedChild", (Requests.RequestWithNestedChild request) => "ok");
    app.MapPost("/requestWithNonNestedChild", (Requests.RequestWithNonNestedChild request) => "ok");

    app.Run("http://*:0");
}

public class Requests
{
    public record RequestWithNestedChild(RequestWithNestedChild.NestedChild Child)
    {
        public record NestedChild(string NonNullable, string? Nullable);
    }

    public record RequestWithNonNestedChild(Child Child);
    public record Child(string NonNullable, string? Nullable);
}

The schema for Child correctly infers nullability

{
    "Child": {
        "type": "object",
        "properties": {
            "nonNullable": {
                "type": "string"
            },
            "nullable": {
                "type": "string",
                "nullable": true
            }
        },
        "additionalProperties": false
    }
}

However the schema for NestedChild incorrectly marks nonNullable as nullable

{
    "NestedChild": {
        "type": "object",
        "properties": {
            "nonNullable": {
                "type": "string",
                "nullable": true
            },
            "nullable": {
                "type": "string",
                "nullable": true
            }
        },
        "additionalProperties": false
    }
}

If I move these records outside of the Request class then nullability is inferred correctly for both

async Task Main()
{
    var builder = WebApplication.CreateBuilder();
    builder.Services.AddEndpointsApiExplorer();
    builder.Services.AddSwaggerGen(options =>
    {
        options.SupportNonNullableReferenceTypes();
    });
    
    var app = builder.Build();
    app.UseSwagger();
    app.UseSwaggerUI();

    app.MapPost("/requestWithNestedChild", (Requests.RequestWithNestedChild request) => "ok");
    app.MapPost("/requestWithNonNestedChild", (Requests.RequestWithNonNestedChild request) => "ok");

    app.Run("http://*:0");
}

public record RequestWithNestedChild(RequestWithNestedChild.NestedChild Child)
{
    public record NestedChild(string NonNullable, string? Nullable);
}

public record RequestWithNonNestedChild(Child Child);
public record Child(string NonNullable, string? Nullable);

Schema

{
    "Child": {
        "type": "object",
        "properties": {
            "nonNullable": {
                "type": "string"
            },
            "nullable": {
                "type": "string",
                "nullable": true
            }
        },
        "additionalProperties": false
    },
    "NestedChild": {
        "type": "object",
        "properties": {
            "nonNullable": {
                "type": "string"
            },
            "nullable": {
                "type": "string",
                "nullable": true
            }
        },
        "additionalProperties": false
    }
}

[craigsmitham]

I just encountered this issue as well.

[jscarle]

I can confirm this. Took me a while to find this issue. This is the really hacky patch I came up as a solution while this gets addressed:

public sealed class NullableSchemaFilter : ISchemaFilter
{
    public void Apply(OpenApiSchema schema, SchemaFilterContext context)
    {
        if (schema.Properties.Count == 0)
            return;

        var nullabilityInfoContext = new NullabilityInfoContext();
        var contextProperties = context.Type.GetProperties();

        foreach (var (name, property) in schema.Properties)
        {
            var contextProperty = contextProperties.FirstOrDefault(x => string.Equals(name, x.Name, StringComparison.OrdinalIgnoreCase));
            if (contextProperty is null)
                continue;

            var nullabilityInfo = nullabilityInfoContext.Create(contextProperty);

            // If nullability is unknown or ambiguous, we continue.
            if (nullabilityInfo is { ReadState: NullabilityState.Unknown, WriteState: NullabilityState.Unknown } || nullabilityInfo.ReadState != nullabilityInfo.WriteState)
                continue;

            var detectedNullability = property.Nullable;
            var reflectedNullability = nullabilityInfo.ReadState == NullabilityState.Nullable;

            if (detectedNullability != reflectedNullability)
                property.Nullable = reflectedNullability;
        }
    }
}

[martincostello]

To make issue tracking a bit less overwhelming for the new maintainers (see #2778), I've created a new tracking issue to roll-up various nullability issues here: #2793.

We'll refer back to this issue from there and include it as part of resolving that issue, but I'm going to close this one to help prune the backlog.