Custom Errors support in require

[SteMak]

Abstract

Since Gas-efficient Custom Errors were added in solidity 0.8.4, the require statement has become mostly unused. The if (!condition) revert CustomError() pattern sometimes looks branchy and makes requirement understanding somewhat harder.

require(min <= value && value <= max, "Value not within bounds");
// comparing to
if (min > value || value > max) revert NotWithinBounds(min, max, value);

I found a workaround, however, it consumes some more Gas compared to ordinary Custom Errors usage.

Motivation

I propose implementing Custom Errors support for the require statement, providing Custom Error as the second parameter instead of an error message.

error NotWithinBounds(uint256 min, uint256 max, uint256 actual);

function checkBounds(uint256 min, uint256 max, uint256 value) external pure {
  require(min <= value && value <= max, NotWithinBounds(min, max, value));
}

Specification

There are several opportunities:

• Make error an ordinary type lazy loads on revert burning

  // Bytes error message is not calculated there
  require(condition, CustomError(params));
  
  function require(bool condition, error err) pure {
    if (!condition) revert err; // Bytes error message is generated here
  }

• Implement inline functions Inline functions / closures / lambdas #12297

  require(condition, () => revert CustomError(params));
  
  function require(bool condition, function() pure handler) pure {
    if (!condition) handler();
  }

• Make the transformation below in compile time

  require(condition, CustomError(params));
  // changed to
  if (!condition) revert CustomError(params);

Backwards Compatibility

As Solidity allows function overloading, the creation of require(bool, error, or other suitable type) should not break backward compatibility.

[agnxsh]

can i take this issue please?

[fulldecent]

I fully support this issue because it increases clarity and expressiveness of the language.

It matches "guards" that other languages have. And a great programming pattern is to put all your guards at the top of a function.

Recognizing that this issue is now labeled as "must have" I have added at to the documentation at #14539

[n00b21337]

Please lets have it.
"If pattern" is really suboptimal.

[luislucena16]

this could be a great implementation for 0.8.26, taking advantage of the arrival of the 0.8.25 fork!!
I will be following this issue!

[wadealexc]

Bumping this -- we really need this feature!

The readability using custom error types is really bad - requiring branching statements for every check really clutters up the code. So we're still using require with error strings - but error strings are inflating our deployment bytecode!

It would be so awesome to be able to use require with custom errors!