View to pure, pure to view

Smart Contracts
1

I want to take a look at this old OpenZeppellin whitelist contract.:

pragma solidity ^0.5.0;
import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v2.1.1/contracts/crowdsale/Crowdsale.sol";
import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v2.1.1/contracts/access/roles/WhitelistedRole.sol";


/**
 * @title WhitelistCrowdsale
 * @dev Crowdsale in which only whitelisted users can contribute.
 */
contract WhitelistCrowdsale is WhitelistedRole, Crowdsale {
    /**
    * @dev Extend parent behavior requiring beneficiary to be whitelisted. Note that no
    * restriction is imposed on the account sending the transaction.
    * @param _beneficiary Token beneficiary
    * @param _weiAmount Amount of wei contributed
    */
    function _preValidatePurchase(address _beneficiary, uint256 _weiAmount) internal view {
        require(isWhitelisted(_beneficiary));
        super._preValidatePurchase(_beneficiary, _weiAmount);
    }
}

When I try to compile I get the following error:

TypeError: Overriding function changes state mutability from "pure" to "view".

Refers to the _preValidatePurchase function
change to view and I get the next:

WhitelistCrowdsale.sol:18:17: TypeError: Function declared as pure, but this expression (potentially) reads from the environment or state and thus requires "view".

How can I get out of this absurd loop?

Is it possible that it has to be inherited in a contract that overrides the functions?

2

If _preValidatePurchase was originally declared as pure, an override also has to be pure.

3

The original WhitelistCrowdsale contract is designated as view.
I have not changed anything.
At least in the contracts that I have found out there.
The solution that I made for is to override the _preValidatePurchase function of the original Crowdsale contract with the corresponding require.

Because using this contract as inheritance gives me this problem.