Add Create2 library (#1744)

* feat(contracts): Add Create2 library to use create2 evm opcode

* Upgrade sol-coverage

* Add changelog entry

* Update comments and code style

* Remove create2 helper

* Fix linter error

* Fix truffle dependency

* Fix linter error

* refactor(Create2): Remove _deploy internal function

* test(Create2): test Create2 with inline assembly code

* fix(Create2): Check address returned form create2 instead of codesize of created contract

.solcover.js

@@ -3,7 +3,6 @@ module.exports = {
     testCommand: 'node --max-old-space-size=4096 ../node_modules/.bin/truffle test --network coverage',
     compileCommand: 'node --max-old-space-size=4096 ../node_modules/.bin/truffle compile --network coverage',
     skipFiles: [
-        'lifecycle/Migrations.sol',
-        'mocks'
+        'mocks',
     ]
 }

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### New features:
  * `Address.toPayable`: added a helper to convert between address types without having to resort to low-level casting. ([#1773](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1773))
  * Facilities to make metatransaction-enabled contracts through the Gas Station Network. ([#1844](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1844))
+ * `Create2`: simple library to make usage of the `CREATE2` opcode easier. ([#1744](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/1744))
 
 ### Improvements:
  * `Address.isContract`: switched from `extcodesize` to `extcodehash` for less gas usage. ([#1802](https://github.com/OpenZeppelin/openzeppelin-solidity/pull/1802))

contracts/mocks/Create2Impl.sol

@@ -0,0 +1,23 @@
+pragma solidity ^0.5.0;
+
+import "../utils/Create2.sol";
+import "../token/ERC20/ERC20.sol";
+
+contract Create2Impl {
+    function deploy(bytes32 salt, bytes memory code) public {
+        Create2.deploy(salt, code);
+    }
+
+    function deployERC20(bytes32 salt) public {
+        // solhint-disable-next-line indent
+        Create2.deploy(salt, type(ERC20).creationCode);
+    }
+
+    function computeAddress(bytes32 salt, bytes memory code) public view returns (address) {
+        return Create2.computeAddress(salt, code);
+    }
+
+    function computeAddress(bytes32 salt, bytes memory code, address deployer) public pure returns (address) {
+        return Create2.computeAddress(salt, code, deployer);
+    }
+}

contracts/utils/Create2.sol

@@ -0,0 +1,49 @@
+pragma solidity ^0.5.0;
+
+/**
+ * @dev Helper to make usage of the `CREATE2` EVM opcode easier and safer.
+ * `CREATE2` can be used to compute in advance the address where a smart
+ * contract will be deployed, which allows for interesting new mechanisms known
+ * as 'counterfactual interactions'.
+ *
+ * See the https://eips.ethereum.org/EIPS/eip-1014#motivation[EIP] for more
+ * information.
+ */
+library Create2 {
+    /**
+     * @dev Deploys a contract using `CREATE2`. The address where the contract
+     * will be deployed can be known in advance via {computeAddress}. Note that
+     * a contract cannot be deployed twice using the same salt.
+     */
+    function deploy(bytes32 salt, bytes memory bytecode) internal returns (address) {
+        address addr;
+        // solhint-disable-next-line no-inline-assembly
+        assembly {
+            addr := create2(0, add(bytecode, 0x20), mload(bytecode), salt)
+            if iszero(addr) {
+                revert(0, 0)
+            }
+        }
+        return addr;
+    }
+
+    /**
+     * @dev Returns the address where a contract will be stored if deployed via {deploy}. Any change in the `bytecode`
+     * or `salt` will result in a new destination address.
+     */
+    function computeAddress(bytes32 salt, bytes memory bytecode) internal view returns (address) {
+        return computeAddress(salt, bytecode, address(this));
+    }
+
+    /**
+     * @dev Returns the address where a contract will be stored if deployed via {deploy} from a contract located at
+     * `deployer`. If `deployer` is this contract's address, returns the same value as {computeAddress}.
+     */
+    function computeAddress(bytes32 salt, bytes memory bytecodeHash, address deployer) internal pure returns (address) {
+        bytes32 bytecodeHashHash = keccak256(bytecodeHash);
+        bytes32 _data = keccak256(
+            abi.encodePacked(bytes1(0xff), deployer, salt, bytecodeHashHash)
+        );
+        return address(bytes20(_data << 96));
+    }
+}

contracts/utils/README.adoc

@@ -8,4 +8,6 @@ Miscellaneous contracts containing utility functions, often related to working w
 
 {{Arrays}}
 
+{{Create2}}
+
 {{ReentrancyGuard}}