Treat at as a reserved keyword in Solidity

[pcaversaccio]

So I was reading through the Solidity 0.8.29 release and checked the new Custom Storage Layout documentation. It's written there:

The identifiers layout and at are not yet reserved as keywords in the language. It is strongly recommended to avoid using them since they will become reserved in a future breaking release.

Now, when I read this I remembered the various at functions in OZ (I probably missed some):

openzeppelin-contracts/contracts/utils/structs/EnumerableSet.sol

Lines 234 to 236 in f740084

	function at(Bytes32Set storage set, uint256 index) internal view returns (bytes32) {
	return _at(set._inner, index);
	}

openzeppelin-contracts/contracts/utils/structs/EnumerableSet.sol

Lines 317 to 319 in f740084

	function at(AddressSet storage set, uint256 index) internal view returns (address) {
	return address(uint160(uint256(_at(set._inner, index))));
	}

openzeppelin-contracts/contracts/utils/structs/Checkpoints.sol

Lines 126 to 128 in f740084

	function at(Trace224 storage self, uint32 pos) internal view returns (Checkpoint224 memory) {
	return self._checkpoints[pos];
	}

openzeppelin-contracts/contracts/utils/structs/Checkpoints.sol

Lines 329 to 331 in f740084

	function at(Trace208 storage self, uint32 pos) internal view returns (Checkpoint208 memory) {
	return self._checkpoints[pos];
	}

openzeppelin-contracts/contracts/utils/structs/Checkpoints.sol

Lines 532 to 534 in f740084

	function at(Trace160 storage self, uint32 pos) internal view returns (Checkpoint160 memory) {
	return self._checkpoints[pos];
	}

[Amxx]

Thank you @pcaversaccio for raising this.

Unfortunatelly, changing the function name would be a breaking change, so I don't think we should do that in 5.x. I would do it in 6.0, which will probably coincide with a bump of solidty version that makes the at keyword reserved anyway.