Add reason string for all assertions/requires

[spalladino]

The next solc version introduces support for reason strings for error messages. As soon as this release is available, migrate to that version and annotate all requires and asserts in the OpenZeppelin codebase with meaningful error messages.

• 📈 This is a feature request.

See argotorg/solidity#3364

[come-maiz]

This was released on solidity 0.4.22. It can be included in openzeppelin now.

[pmosse]

@ElOpio @spalladino I can work on this. Do you have any guidelines for the messages (for example to make them as short as possible)? Or should I do a PR with a couple of sample cases so we can check?

[come-maiz]

@pmosse we have no guidelines yet, so why don't you go ahead and propose some? We can discuss on the PR.

[pmosse]

@ElOpio Done!

[shrugs]

I'd like to bring up the problem of having english error messages as return values instead of, say, status codes via https://eips.ethereum.org/EIPS/eip-1066

[shrugs]

At the very least, errors should be referred to as constants, imo

[pmosse]

Good idea. English error messages have more specific information but status codes facilitate automation. Should we have a global list of status codes constants? We can extend https://github.com/Finhaven/EthereumStatusCodes with others such as "Not Enough Funds". @ElOpio what are your thoughts on this?

[come-maiz]

Sorry for the late reply, I had to read the EIP. omg so many eips!!!
The idea sounds very nice, but it also sounds like it will take a long time for the community to agree on the form and the codes. We can update to that format once it's accepted.

About using constants, I have weird feelings towards constants that are upper-cased copies of strings, like:

ERROR_MESSAGE_NOT_ENOUGH_FUNDS_TO_DO_PAYMENT = "Not enough funds to do the payment";

If we have repeated messages, it could be useful. But from your PR we can't tell if we'll repeat any of them. I think it could be a premature optimization, but I'm not against it. If @shrugs wants them, go ahead.

We can also ask @frangio, he might have a strong opinion.
Anyway, your pr is a nice addition and we can iterate on it until it's perfect :) Thanks for that.