Always raising “Gas required exceeds allowance or always failing transaction” when the condition of require() is not met

Question

I tried to run the following code to check the error message when the condition of require() is not met.

pragma solidity ^0.5.16;
...
function addUser(string memory name) public returns (int) {
   require(!userList[msg.sender].isSigned, "You already have an account.");
   ...
}

When the condition of require() is met, it worked as expected, but when the condition wasn't met, I could always see the following error message:

transact to Messenger.addUser errored: gas required exceeds allowance (8946128) or always failing transaction

I thought that the problem was due to the gas limit of the block, so I increased the gas limit from ten thousand to one million. However, the problem was not solved and I don't know what the cause is.

What I want to ask is

• Does solidity always show that error message when the condition of require() is not met?
• How to check the message("You already have an account.") I specified in require()?

Thanks for help :)

Answer 1

Does solidity always show that error message when the condition of require is not met?

First of all, it is not Solidity which generates this error-message, it is Web3.js.

Second, it is indeed arguably not the most suitable error-message because it makes one think that it has something to do with the gas, where in fact the transaction reverts because the condition of the require is not met. But if you take a good look at that message, then you'll see "or always failing transaction", which aligns perfectly with the reason of the failure.