Merge branch 'solc-0.7' into solc-0.8

contracts/utils/Context.sol

@@ -0,0 +1,24 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity >=0.6.0 <0.9.0;
+
+/*
+ * @dev Provides information about the current execution context, including the
+ * sender of the transaction and its data. While these are generally available
+ * via msg.sender and msg.data, they should not be accessed in such a direct
+ * manner, since when dealing with GSN meta-transactions the account sending and
+ * paying for execution may not be the actual sender (as far as an application
+ * is concerned).
+ *
+ * This contract is only required for intermediate, library-like contracts.
+ */
+abstract contract Context {
+    function _msgSender() internal view virtual returns (address) {
+        return msg.sender;
+    }
+
+    function _msgData() internal view virtual returns (bytes memory) {
+        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
+        return msg.data;
+    }
+}

contracts/utils/EnumerableMap.sol

@@ -143,6 +143,16 @@ library EnumerableMap {
         return (entry._key, entry._value);
     }
 
+    /**
+     * @dev Tries to returns the value associated with `key`.  O(1).
+     * Does not revert if `key` is not in the map.
+     */
+    function _tryGet(Map storage map, bytes32 key) private view returns (bool, bytes32) {
+        uint256 keyIndex = map._indexes[key];
+        if (keyIndex == 0) return (false, 0); // Equivalent to contains(map, key)
+        return (true, map._entries[keyIndex - 1]._value); // All indexes are 1-based
+    }
+
     /**
      * @dev Returns the value associated with `key`.  O(1).
      *
@@ -151,11 +161,16 @@ library EnumerableMap {
      * - `key` must be in the map.
      */
     function _get(Map storage map, bytes32 key) private view returns (bytes32) {
-        return _get(map, key, "EnumerableMap: nonexistent key");
+        uint256 keyIndex = map._indexes[key];
+        require(keyIndex != 0, "EnumerableMap: nonexistent key"); // Equivalent to contains(map, key)
+        return map._entries[keyIndex - 1]._value; // All indexes are 1-based
     }
 
     /**
      * @dev Same as {_get}, with a custom error message when `key` is not in the map.
+     *
+     * CAUTION: This function is deprecated because it requires allocating memory for the error
+     * message unnecessarily. For custom revert reasons use {_tryGet}.
      */
     function _get(Map storage map, bytes32 key, string memory errorMessage) private view returns (bytes32) {
         uint256 keyIndex = map._indexes[key];
@@ -217,6 +232,15 @@ library EnumerableMap {
         return (uint256(key), address(uint160(uint256(value))));
     }
 
+    /**
+     * @dev Tries to returns the value associated with `key`.  O(1).
+     * Does not revert if `key` is not in the map.
+     */
+    function tryGet(UintToAddressMap storage map, uint256 key) internal view returns (bool, address) {
+        (bool success, bytes32 value) = _tryGet(map._inner, bytes32(key));
+        return (success, address(uint160(uint256(value))));
+    }
+
     /**
      * @dev Returns the value associated with `key`.  O(1).
      *
@@ -230,6 +254,9 @@ library EnumerableMap {
 
     /**
      * @dev Same as {get}, with a custom error message when `key` is not in the map.
+     *
+     * CAUTION: This function is deprecated because it requires allocating memory for the error
+     * message unnecessarily. For custom revert reasons use {tryGet}.
      */
     function get(UintToAddressMap storage map, uint256 key, string memory errorMessage) internal view returns (address) {
         return address(uint160(uint256(_get(map._inner, bytes32(key), errorMessage))));

contracts/utils/Pausable.sol

@@ -2,7 +2,7 @@
 
 pragma solidity ^0.8.0;
 
-import "../GSN/Context.sol";
+import "./Context.sol";
 
 /**
  * @dev Contract module which allows children to implement an emergency stop
@@ -36,7 +36,7 @@ abstract contract Pausable is Context {
     /**
      * @dev Returns true if the contract is paused, and false otherwise.
      */
-    function paused() public view returns (bool) {
+    function paused() public view virtual returns (bool) {
         return _paused;
     }
 
@@ -48,7 +48,7 @@ abstract contract Pausable is Context {
      * - The contract must not be paused.
      */
     modifier whenNotPaused() {
-        require(!_paused, "Pausable: paused");
+        require(!paused(), "Pausable: paused");
         _;
     }
 
@@ -60,7 +60,7 @@ abstract contract Pausable is Context {
      * - The contract must be paused.
      */
     modifier whenPaused() {
-        require(_paused, "Pausable: not paused");
+        require(paused(), "Pausable: not paused");
         _;
     }