New ABI decoder fails on arrays of dynamic types as calldata

[axic]

pragma experimental ABIEncoderV2;

contract C {
  function f(string[]) external {}    
}

throws assertion

Internal compiler error during compilation:
/Users/alex/Projects/solidity/libsolidity/codegen/ABIFunctions.cpp(1188): Throw in function string dev::solidity::ABIFunctions::abiDecodingFunctionCalldataArray(const dev::solidity::ArrayType &)
Dynamic exception type: boost::exception_detail::clone_impl<dev::solidity::InternalCompilerError>
std::exception::what: 
[dev::tag_comment*] = 

Which means arrays of dynamic types cannot be decoded as calldata. Though changing it to public will make it working, because the decoder is invoked elsewhere.

[carver]

Is this maybe related to external functions handling strings a little differently in ABI encoding? See my open question: https://ethereum.stackexchange.com/questions/39418/why-do-public-and-external-functions-emit-strings-differently-in-event-logs

I posted #3493 to track that issue.

[chriseth]

This is unimplemented mainly due to the fact that we did not yet decide how such types are stored on the stack. It was not a problem for the old decoder because it only supported one-dimensional arrays. Those are stored with two stack items: offset and size.

I guess if we know the type, it should still be possible to do that by just storing the type. Still, a lot of infrastructure is still missing - you cannot copy multi-dimensional calldata arrays to memory or storage.

[axic]

After 0.5.0:

pragma experimental ABIEncoderV2;
contract C {
  function f(string[] calldata) external {}    
}

Unimplemented feature:
/Users/alex/Projectssolidity/libsolidity/codegen/ABIFunctions.cpp(1294): Throw in function std::__1::string dev::solidity::ABIFunctions::abiDecodingFunctionCalldataArray(const dev::solidity::ArrayType &)
Dynamic exception type: boost::exception_detail::clone_impl<langutil::UnimplementedFeatureError>
std::exception::what: Calldata arrays with non-value base types are not yet supported by Solidity.
[dev::tag_comment*] = Calldata arrays with non-value base types are not yet supported by Solidity.

[axic]

What is funny, without the ABIEncoderV2 pragma the message is:

3293.sol:4:14: Error: This type is only supported in the new experimental ABI encoder. Use "pragma experimental ABIEncoderV2;" to enable the feature.
  function f(string[] calldata) external {}    
             ^---------------^