Disallow returning Vec (and any raw_ptr) from a contract to another contract

[mohammadfawaz]

Returning a Vec from one contract to another should be disallowed because the pointer from the called contract is not valid in the caller contract. The same check that we have that disallows returning raw_ptr from scripts should also be used in this case.

[mohammadfawaz]

Here's a simple example:

library with an ABI:

library external_abi;

abi MyAbi {
    fn foo() -> Vec <u64>;
}

Contract:

contract;

dep external_abi;

use external_abi::MyAbi;

abi MyContract {
    fn bar();
}

impl MyContract for Contract {
    fn bar() {
        let caller = abi(MyAbi, 0x0000000000000000000000000000000000000000000000000000000000000000);

        let result:Vec<u64> = caller.foo(); // This should be an error
    }
}

The idea is going to be to return a slice instead.

[adlerjohn]

Ackchyually you should be able to return a Vec from a contract! Since there is no deallocation, a returned pointer will still be valid. However, the caller will have to make sure the data pointed to remains valid by allocating space for the underlying data.