ICE on calling externally a function that returns calldata pointers

[haltman-at]

Description

As of Solidity 0.6.9, it is possible for functions to return calldata pointers. If such a function is called externally, an InternalCompilerError results.

Suggested fix: Since I don't think there's really any sensible way to handle calling such a function externally, only internal and private functions should be allowed to return calldata pointers.

Environment

• Compiler version: 0.6.9
• Target EVM version (as per compiler settings): default
• Framework/IDE (e.g. Truffle or Remix): Truffle

Steps to Reproduce

//SPDX-License-Identifier: MIT
pragma solidity ^0.6.9;

contract CalldataTest {
  function test(bytes calldata x) public returns (bytes calldata) {
    return x;
  }
  function tester(bytes calldata x) public {
    this.test(x);
  }
}

Attempting to compile this yields an ICE.

[chriseth]

Right before the release, I thought "did we actually test this"? We did, and it worked, but I only tested the test function via remix, not the tester :)

I think the bug is that FunctionType::asExternallyCallableFunction does not properly change the location of the return variables, only the parameters.