Throws during pure calls to library functions

Hello sc team,

Recently we have attempted to upgrade to newer version of solidity as well as solidity-coverage and found some issues that took a very long time to track down.

I have created a very minimal example to show the issue which can be found here.

Essentially, a .call() to a pure library function is throwing Error: VM Exception while processing transaction: revert in the coverage environment.

If you take a look at the repo, the instructions to reproduce are there.

According to the docs of solidity 0.4.23 this should be possible and has worked in the past

Library functions can only be called directly (i.e. without the use of DELEGATECALL) if they do not modify the state (i.e. if they are view or pure functions), because libraries are assumed to be stateless

please let me know what other information I can help provide to get this resolved. I think the repo should help bring out the issue pretty clearly.

Thanks for all you guys do!

[cgewecke]

Hi @pelsasser. Thanks so much for opening. Quite sorry because this issue is known and should have been documented. It was discovered by Zeppelin about a month ago (more detail in this thread)

The underlying issue is that solidity-coverage rewrites the contract ABIs of pure/view functions in order to sneak event-based instrumentation into the contracts during compilation. It then swaps the original ABIs back into the contract artifacts to get truffle to call the functions correctly. (e.g. as calls, not transactions).

Since 0.4.20, in response to Parity’s wallet being deleted, solc has added protections (at the bytecode level) that prevent non-view library methods from being called directly. TLDR, the pure library functions are being compiled as non-view functions and this triggers the error.

A work-around is to call these library methods through a mock contract that uses the library.

• an example at Zeppelin here
• mocks must be located in the contracts directory (not test). You can put them in a mocks folder.
• mock contracts themselves can be excluded from coverage using the skipFiles option in .solcover.js, e.g

  skipFiles: [
        'lifecycle/Migrations.sol', // <-- single file
        'mocks' // <-- whole folder
    ]
  

• if you are publishing your contracts to npm you’ll probably want to .npmignore your mocks folder

[cgewecke]

Fixed with 0.7.0