Limitations on dynamically-sized structs

[iamdefinitelyahuman]

Structs containing dynamically sized types (string, bytes) are not fully supported in vyper.

The following actions fail to compile and produce exceptions that are not immediately obvious:

• An argument in an external function call
• An argument in an internal function call
• An input argument for function - but only if you attempt to access the dynamically sized data

The following actions are supported:

• returning from an internal function
• returning from an external function

As a temporary measure I've added a better exception during type checking (#2189). It covers all of the not-possible cases given above. Going forward though, I think we should add support for these structs in the places where they aren't working.

[vasa-develop]

How difficult is it to add support for these cases? (In case I would take a stab at this)

[fubuloubu]

@vasa-develop we have some of the building blocks in place (abi encoder), but it would be difficult to do this quickly without spending a lot of time in the codebase. Worth a shot if you have the time though, I know this is blocking you. We can help in TG if you need answers

[charles-cooper]

fixed in #2447