[Ethereum] Explicit type conversion not allowed from “bytes1” to “uint256”

I don't think it ever was because bytes is a dynamic array of byte which means it has a length. Is it possible you saw bytes32 conversion to unit? That is totally acceptable in that both are 32-byte words.

This compiles under 0.4.25 as well 0.5.2.

contract Bytes {

    function convert(bytes32 b) public pure returns(uint) {
        return uint(b);
    }
}

On the other hand, this conversion is trouble in all cases I'm aware of.

contract Bytes {

    function convert(bytes b) public pure returns(uint) {
        return uint(b);
    }
}

In my opinion, conversion of bytes and string to numbers, string manipulation, etc. are problematic issues that should usually be dealt with by software clients rather than burdening contracts with such concerns. It's a case where the contract team should strongly resist overloading the contract with concerns that software clients are capable of resolving.

Hope it helps.

You are getting this error because you are trying to take the keccack256 hash of a uint, which you cannot do, according to the docs. What you must do instead is convert the uint to a bytes.

The code you want is as follows:

function random() private returns(uint){
    uint source = block.difficulty + now;
    bytes memory source_b = toBytes(source);
    return uint(keccak256(source_b));
}

function toBytes(uint256 x) public returns (bytes memory b) {
    b = new bytes(32);
    assembly { mstore(add(b, 32), x) }
}