Delegate calls

Delegate calls are function calls against a contract class identifier instead of an instance. Any call -- synchronous or asynchronous -- can be made as a delegate call. The behavior of a delegate call is to execute the function code in the specified class identifier but in the context of the current instance. This opens the door to script-like executions and upgradeable contracts. Delegate calls are based on EIP7.

At the protocol level, a delegate call is identified by a is_delegate_call flag in the CircuitPublicInputs of the CallStackItem. The contract_address field is reinterpreted as a contract class instead. When executing a delegate call, the kernel preserves the values of the CallContext msgSender and storageContractAddress.

At the contract level, a caller can initiate a delegate call via a delegateCallPrivateFunction or delegateCallPublicFunction oracle call. The caller is responsible for asserting that the returned CallStackItem has the is_delegate_call flag correctly set.