Support recursive types in parameterized records

[jyemin]

Provide codec support for records whose type declarations contain cycles.

JAVA-4745

Looking for feedback on the general approach. The codec registry changes could use some more unit tests if we want to proceed with this.

[rozza]

Interesting, would an alternative be to keep this within the RecordCodec implementaiton - so no changes to the CodecRegistry?

For example would just adding a LazyRecordCodec be enough to break any cycles eg:

class LazyRecordCodec<T> implements Codec<T> {
    private final Supplier<Codec<T>> supplier;
    private volatile Codec<T> wrapped;

    LazyRecordCodec(final Supplier<Codec<T>> supplier) {
        this.supplier = supplier;
    }

    @Override
    public void encode(final BsonWriter writer, final T value, final EncoderContext encoderContext) {
        getWrapped().encode(writer, value, encoderContext);
    }

    @Override
    public Class<T> getEncoderClass() {
        return  getWrapped().getEncoderClass();
    }

    @Override
    public T decode(final BsonReader reader, final DecoderContext decoderContext) {
        return getWrapped().decode(reader, decoderContext);
    }

    private Codec<T> getWrapped() {
        if (wrapped == null) {
            wrapped = supplier.get();
        }
        return wrapped;
    }
}

Then the codec could be:

this.codec = new LazyRecordCodec<>(() -> computeCodec(typeParameters, component, codecRegistry));

The downside is it makes all records codecs lazy but the upside would be no changes required outside the RecordCodec.

[jyemin]

Yes, I think we could handle cycles outside the registry. But it's cleaner if we put it in the registry, and we get the additional benefit of caching parameterized types.

[rozza]

One question - but its looking good