[Bug]: Update to 8.1.2 produces an exception while generating swagger

[dmytro-gokun]

Describe the bug

I have this code:

namespace MyProject;

public enum AAAType {}
public enum BBBType {}

[Route("xxx")]
public sealed class XXXController
{
    public sealed record CreateXXXRequest(
         AAAType? TypeA,
         BBBType? TypeB
    );

    [HttpPost]
    public async Task<XXXResponse> CreateXXX([FromBody] CreateXXXRequest request, CancellationToken 
             cancellationToken)
    {
    }
}

Generating swagger for this results in exception:

     Swashbuckle.AspNetCore.SwaggerGen.SwaggerGeneratorException: Failed to generate Operation for action - XXXController.CreateXXX (MyProject). See inner exception
       ---> Swashbuckle.AspNetCore.SwaggerGen.SwaggerGeneratorException: Failed to generate schema for type - MyProject.XXXController+CreateXXXRequest. See inner exception
       ---> System.InvalidOperationException: Can't use schemaId "$Nullable`1" for type "$System.Nullable`1[MyProject.AAAType]". The same schemaId is already used for type "$System.Nullable`1[MyProject.BBBType]"
         at Swashbuckle.AspNetCore.SwaggerGen.SchemaRepository.RegisterType(Type type, String schemaId)
         at Swashbuckle.AspNetCore.SwaggerGen.SchemaGenerator.GenerateReferencedSchema(DataContract dataContract, SchemaRepository schemaRepository, Func`1 definitionFactory)
         at Swashbuckle.AspNetCore.SwaggerGen.SchemaGenerator.GenerateConcreteSchema(DataContract dataContract, SchemaRepository schemaRepository)
         at Swashbuckle.AspNetCore.SwaggerGen.SchemaGenerator.GenerateSchemaForMember(Type modelType, SchemaRepository schemaRepository, MemberInfo memberInfo, DataProperty dataProperty)
         at Swashbuckle.AspNetCore.SwaggerGen.SchemaGenerator.CreateObjectSchema(DataContract dataContract, SchemaRepository schemaRepository)
         at Swashbuckle.AspNetCore.SwaggerGen.SchemaGenerator.<>c__DisplayClass13_0.<GenerateConcreteSchema>b__3()
         at Swashbuckle.AspNetCore.SwaggerGen.SchemaGenerator.GenerateReferencedSchema(DataContract dataContract, SchemaRepository schemaRepository, Func`1 definitionFactory)
         at Swashbuckle.AspNetCore.SwaggerGen.SchemaGenerator.GenerateConcreteSchema(DataContract dataContract, SchemaRepository schemaRepository)
         at Swashbuckle.AspNetCore.SwaggerGen.SchemaGenerator.GenerateSchemaForParameter(Type modelType, SchemaRepository schemaRepository, ParameterInfo parameterInfo, ApiParameterRouteInfo routeInfo)
         at Swashbuckle.AspNetCore.SwaggerGen.SchemaGenerator.GenerateSchema(Type modelType, SchemaRepository schemaRepository, MemberInfo memberInfo, ParameterInfo parameterInfo, ApiParameterRouteInfo routeInfo)
         at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateSchema(Type type, SchemaRepository schemaRepository, PropertyInfo propertyInfo, ParameterInfo parameterInfo, ApiParameterRouteInfo routeInfo)
         --- End of inner exception stack trace ---
         at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateSchema(Type type, SchemaRepository schemaRepository, PropertyInfo propertyInfo, ParameterInfo parameterInfo, ApiParameterRouteInfo routeInfo)
         at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateRequestBodyFromBodyParameter(ApiDescription apiDescription, SchemaRepository schemaRepository, ApiParameterDescription bodyParameter)
         at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateRequestBodyAndFilterContext(ApiDescription apiDescription, SchemaRepository schemaRepository)
         at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateRequestBodyAsync(ApiDescription apiDescription, SchemaRepository schemaRepository)
         at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateOperationAsync(OpenApiDocument document, ApiDescription apiDescription, SchemaRepository schemaRepository, Func`3 parametersGenerator, Func`3 bodyGenerator, Func`3 applyFilters)
         --- End of inner exception stack trace ---
         at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateOperationAsync(OpenApiDocument document, ApiDescription apiDescription, SchemaRepository schemaRepository, Func`3 parametersGenerator, Func`3 bodyGenerator, Func`3 applyFilters)
         at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateOperationAsync(OpenApiDocument document, ApiDescription apiDescription, SchemaRepository schemaRepository)
         at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GenerateOperationsAsync(OpenApiDocument document, IEnumerable`1 apiDescriptions, SchemaRepository schemaRepository)
         at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GeneratePathsAsync(OpenApiDocument document, IEnumerable`1 apiDescriptions, SchemaRepository schemaRepository, Func`4 operationsGenerator)
         at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GeneratePathsAsync(OpenApiDocument document, IEnumerable`1 apiDescriptions, SchemaRepository schemaRepository)
         at Swashbuckle.AspNetCore.SwaggerGen.SwaggerGenerator.GetSwaggerAsync(String documentName, String host, String basePath)
         at Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext httpContext, ISwaggerProvider swaggerProvider)
         at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.HttpProtocol.ProcessRequests[TContext](IHttpApplication`1 application)

This was not the case before update to 8.1.2

[martincostello]

Thanks for reporting this issue.

A likely candidate for causing this is probably #3377 - @ItsVeryWindy would you be able to take a look please?

[ItsVeryWindy]

@dmytro-gokun are you able to confirm if you're configuring CustomSchemaIds anywhere? if so, can you show what config you've setup for it.

Does it maybe look similar to but not necessarily exactly like this

Swashbuckle.AspNetCore/docs/configure-and-customize-swaggergen.md

Line 576 in 85baafc

options.CustomSchemaIds((type) => type.FullName);

?

[dmytro-gokun]

@ItsVeryWindy You are right, we have customer schema IDs in this project. I've been able to work this around. Thanks for your help!