ABI does not match solidity in the case of returning a single struct

[charles-cooper]

Version Information

• vyper Version (output of vyper --version): v0.2.16

What's your issue about?

Solidity does not allow return types which are not wrapped in a tuple. For instance, the following signature is illegal Solidity:

struct Person { bytes name; int age; }
function person() external returns Person memory;

Instead, the signature must be something like

function person() external view returns (Person memory);

(this is equivalent to vyper returning (Person,))

We can do it either way in vyper since we don't have the same semantic restriction, but for simple types (bytestrings and base types), we already wrap them in a tuple for compatibility. We should be consistent for structs and wrap them in a tuple as needed.

[fubuloubu]

Seems like a reasonable compatibility point

[charles-cooper]

fixed in #2447