xdr: optional typedef generates an invalid xdr_generated.go

[abuiles]

Protocol 14 includes a new type called SponsorshipDescriptor which is defined as an alias to an Optional AccountId

typedef AccountID* SponsorshipDescriptor;

The code generated by xdrgen produces an invalid output (see failure here stellar/go@3b2053c)

As a temporary workaround, I removed the marshaling/unmarshaling methods from SponsorshipDescriptor which solves the problem and makes the type behave as expected, which is an optional field -- when reading from a raw XDR it will try to read the first 4 bytes to determine if it is void or not and then read the content.

abuiles/go@5c48fa9

This unblocks https://github.com/stellar/go/pull/2864 and allows us to move forward with Protocol 14 support.

This seems like a bug on xdrgen when compiling to go (it does the right thing in JS), maybe for optional typedefs we don't need marshaling and unmarshalling since we can delegate to the struct being referenced.

I also put a simple demo here https://github.com/abuiles/xdr-test/blob/master/src/main.go which shows a similar XDR definition working fine.

[bartekn]

I think this affects all languages generated by xdrgen. Should we move the issue there?

[abuiles]

@bartekn It does the right thing for JavaScript but I didn't check the other languages.

[leighmcculloch]

I transferred this issue from the stellar/go repo to the stellar/xdrgen repo because I hit the same issue and started opening an issue and initially didn't see the issue because it was in the go repo. Regardless of whether this impacts all languages I think this is something we need to fix in xdrgen, not stellar/go.

To add some more details to this issue the specific errors I get are below.

I'm using:

• xdrgen version 9dacf24
• xdr files from stellar/stellar-core@872f4be:

# github.com/stellar/go/xdr
xdr/xdr_generated.go:1599:6: invalid receiver type SponsorshipDescriptor (SponsorshipDescriptor is a pointer type)
xdr/xdr_generated.go:1606:6: invalid receiver type *SponsorshipDescriptor (SponsorshipDescriptor is a pointer type)
xdr/xdr_generated.go:1612:2: cannot use (*SponsorshipDescriptor)(nil) (type *SponsorshipDescriptor) as type encoding.BinaryMarshaler in assignment:
        *SponsorshipDescriptor does not implement encoding.BinaryMarshaler (missing MarshalBinary method)
xdr/xdr_generated.go:1613:2: cannot use (*SponsorshipDescriptor)(nil) (type *SponsorshipDescriptor) as type encoding.BinaryUnmarshaler in assignment:
        *SponsorshipDescriptor does not implement encoding.BinaryUnmarshaler (missing UnmarshalBinary method)

[leighmcculloch]

PR #64 hacked around this issue so at least we now continue to build valid Go code, and marshaling/unmarshaling still works, we just do it a bit differently for this type. So the issue isn't completely resolved, but in practice it shouldn't cause us problems with generating Go code.

I kept the issue open though in case we want to find a more elegant solution or something better.

Related to this issue I opened a proposal at golang/go#48592 proposing that receiver pointer base types become supported in Go. That would be the ultimate win for this issue I think, but we'll see.