Feature/Adding RoleAdminChanged event in AccessControl (#2214)

* Emit new event RoleAdminChanged

* Adding new RoleAdminChanged event in Tests

* Update suggested comments on new Event

Co-authored-by: Nicolás Venturo <nicolas.venturo@gmail.com>

* Adding PreviousAdminRole to event

* Update AccessControl.test.js

* Update CHANGELOG.md

Co-authored-by: Nicolás Venturo <nicolas.venturo@gmail.com>

CHANGELOG.md

 # Changelog
 
+## 3.1.0 (unreleased)
+
+### Improvements
+ * `AccessControl`: added a `RoleAdminChanged` event to `_setAdminRole`. ([#2214](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2214))
+
 ## 3.0.1 (2020-04-27)
 
 ### Bugfixes

contracts/access/AccessControl.sol

@@ -53,6 +53,14 @@ abstract contract AccessControl is Context {
     bytes32 public constant DEFAULT_ADMIN_ROLE = 0x00;
 
     /**
+     * @dev Emitted when `newAdminRole` is set as ``role``'s admin role, replacing `previousAdminRole`
+     *
+     * `DEFAULT_ADMIN_ROLE` is the starting admin for all roles, despite
+     * {RoleAdminChanged} not being emitted signaling this.
+     */
+    event RoleAdminChanged(bytes32 indexed role, bytes32 indexed previousAdminRole, bytes32 indexed newAdminRole);
+
+    /**
      * @dev Emitted when `account` is granted `role`.
      *
      * `sender` is the account that originated the contract call, an admin role
@@ -183,8 +191,11 @@ abstract contract AccessControl is Context {
 
     /**
      * @dev Sets `adminRole` as ``role``'s admin role.
+     *
+     * Emits a {RoleAdminChanged} event.
      */
     function _setRoleAdmin(bytes32 role, bytes32 adminRole) internal virtual {
+        emit RoleAdminChanged(role, _roles[role].adminRole, adminRole);
         _roles[role].adminRole = adminRole;
     }
 

test/access/AccessControl.test.js

@@ -142,7 +142,13 @@ describe('AccessControl', function () {
 
   describe('setting role admin', function () {
     beforeEach(async function () {
-      await this.accessControl.setRoleAdmin(ROLE, OTHER_ROLE);
+      const receipt = await this.accessControl.setRoleAdmin(ROLE, OTHER_ROLE);
+      expectEvent(receipt, 'RoleAdminChanged', {
+        role: ROLE, 
+        previousAdminRole: DEFAULT_ADMIN_ROLE, 
+        newAdminRole: OTHER_ROLE 
+      });
+      
       await this.accessControl.grantRole(OTHER_ROLE, otherAdmin, { from: admin });
     });