Incorrect ABI for returning struct from a mapping

[fubuloubu]

Version Information

• vyper Version (output of vyper --version): 0.2.3

What's your issue about?

See ethereum/web3.py#1634 (comment)

For ABIs that return structs/tuples, the ABI encoding that is maximally efficient is to not wrap it in a tuple if it is the base-level return value. This is sort of an unwritten rule of ABI encoding.

How can it be fixed?

I think just the ABI that we produce is wrong, the encoding seems to be correct: ethereum/web3.py#1634 (comment)