Merge branch 'solc-0.7' into solc-0.8

contracts/proxy/Initializable.sol

@@ -3,16 +3,17 @@
 // solhint-disable-next-line compiler-version
 pragma solidity ^0.8.0;
 
+import "../utils/Address.sol";
 
 /**
  * @dev This is a base contract to aid in writing upgradeable contracts, or any kind of contract that will be deployed
  * behind a proxy. Since a proxied contract can't have a constructor, it's common to move constructor logic to an
  * external initializer function, usually called `initialize`. It then becomes necessary to protect this initializer
  * function so it can only be called once. The {initializer} modifier provided by this contract will have this effect.
- * 
+ *
  * TIP: To avoid leaving the proxy in an uninitialized state, the initializer function should be called as early as
  * possible by providing the encoded function call as the `_data` argument to {UpgradeableProxy-constructor}.
- * 
+ *
  * CAUTION: When used with inheritance, manual care must be taken to not invoke a parent initializer twice, or to ensure
  * that all initializers are idempotent. This is not verified automatically as constructors are by Solidity.
  */
@@ -49,15 +50,6 @@ abstract contract Initializable {
 
     /// @dev Returns true if and only if the function is running in the constructor
     function _isConstructor() private view returns (bool) {
-        // extcodesize checks the size of the code stored in an address, and
-        // address returns the current address. Since the code is still not
-        // deployed when running a constructor, any checks on its code size will
-        // yield zero, making it an effective way to detect if a contract is
-        // under construction or not.
-        address self = address(this);
-        uint256 cs;
-        // solhint-disable-next-line no-inline-assembly
-        assembly { cs := extcodesize(self) }
-        return cs == 0;
+        return !Address.isContract(address(this));
     }
 }