smallrye-graphql: Add ability for users to add error code

Hello there,

I’m a new person to GraphQL but in the last few days I was experimenting with it within the Quarkus framework, and I’m liking it so far. When it comes to writing code sometimes error can occur and I like to specify the error via error codes or with reasons which are straightforward and can be consumed easily by the caller. In the official GraphQL specification there are a few section about errors and one of them is specifying how the programmers could define “custom” error codes in their responses. Take a look at here: https://spec.graphql.org/June2018/#example-fce18

So what I see there if the programmer would like to indicate any kind of custom behavior in the error response they just have to put this information into the extension section in a key-value format. Easy. The problem with that in the SmallRye implementation this kind of stuff is not working properly (yet).

An example: I have a GraphQL API like the following:

@GraphQLApi
public class PackageResource {

    @Query("getPackages")
    @Description("Returns all available packages")
    public List<Package> getPackages() {
        throw GraphqlErrorException.newErrorException()
                .message("Something went wrong")
                .extensions(Map.of("code","CUSTOM_ERROR_CODE"))
                .build();
    }

}

I found the GraphqlErrorException class and it looks fine, because it has an extensions variable in it and it can be populated, so far so good, btw this class is coming from the com.graphql-java:graphql-java:14.0 dependency right now. So when this exception is being thrown it will be handled by the io.smallrye.graphql.execution.error.ExceptionHandler where it will be wrapped as a io.smallrye.graphql.execution.error.GraphQLExceptionWhileDataFetching exception which calls it’s super class constructor graphql.ExceptionWhileDataFetching and it sets any kind of incoming extensions in it.

public ExceptionWhileDataFetching(ExecutionPath path, Throwable exception, SourceLocation sourceLocation) {
        this.path = assertNotNull(path).toList();
        this.exception = assertNotNull(exception);
        this.locations = Collections.singletonList(sourceLocation);
        this.extensions = mkExtensions(exception);
        this.message = mkMessage(path, exception);
    }

At this point if a newly created exception is containing extra extensions then it will be populated there. The problems comes when this exception is being serialized by the io.smallrye.graphql.execution.error.ExecutionErrorsService#toJsonError method. It basically “replaces” or just simply ignores the content of the extensions field. io.smallrye.graphql.execution.error.ExecutionErrorsService#getDataFetchingExtensions

    private Optional<JsonObject> getDataFetchingExtensions(ExceptionWhileDataFetching error) {
        Throwable exception = error.getException();

        JsonObjectBuilder objectBuilder = jsonBuilderFactory.createObjectBuilder();

        addKeyValue(objectBuilder, EXCEPTION, exception.getClass().getName());
        addKeyValue(objectBuilder, CLASSIFICATION, error.getErrorType().toString());

        return Optional.of(objectBuilder.build());
    }

So my question is the following, is there any way to populate the response with the values in the extensions field within the ExceptionWhileDataFetching exception? If there is no specific reason for ignoring the custom values then I think a change could be made to the getDataFetchingExtensions method, if there is a specific reason for ignoring them, then please ignore this issue ticket 😃