Feature/patch token decimals into voucher hub (#50)

CHANGELOG.md

@@ -1,19 +1,23 @@
 # Changelog
 
 ## vNEXT
+
 - Remove references to blockscout v5. (#49)
+- Override the decimals function of ERC-20 to set the token's decimal precision to 9, aligning with RLC standards. (#50)
 - Verify VoucherProxy contracts. (#51)
 
 ## v1.0.0
 
 ### What's new?
+
 - Allow users to access resources of the iExec network via a sponsorship voucher.
 
 ### More details
+
 - Upgrade Solidity Compiler to `v0.8.27`. (#45)
 - Bump dependencies: (#44)
-    - `@openzeppelin/hardhat-upgrades`, `hardhat`, `ethers`, `prettier`, and others [minor version bump]
-    - `prettier-plugin-organize-imports@4`
+  - `@openzeppelin/hardhat-upgrades`, `hardhat`, `ethers`, `prettier`, and others [minor version bump]
+  - `prettier-plugin-organize-imports@4`
 - Add `getVoucherProxyCodeHash(..)` & `isRefundedTask(..)` view functions. (#43)
 - Add `predictVoucher(..)` & `isVoucher(..)` functions. (#42)
 - Generate UML class diagram for contracts. (#41)
@@ -44,12 +48,12 @@
 - Match orders through voucher. (#12)
 - Add external-hardhat network configuration. (#11)
 - Add voucher credit and SRLC manipulation. (#10)
-    - SRLC and iExec poco is mocked.
-    - set voucher credit as VoucherHub is ERC20.
+  - SRLC and iExec poco is mocked.
+  - set voucher credit as VoucherHub is ERC20.
 - Upgrade configuration: (#9)
-    - Upgrade dependencies: hardhat, husky, iExec Poco.
-    - Ignore mocks in coverage.
-    - Add solidity optimizer and use Bellecour network config.
+  - Upgrade dependencies: hardhat, husky, iExec Poco.
+  - Ignore mocks in coverage.
+  - Add solidity optimizer and use Bellecour network config.
 - Add role-based access control to VoucherHub. (#8)
 - Create voucher from VoucherHub with : type, expiration, authorize list. (#6)
 - Create vouchers with create2. (#5)

contracts/NonTransferableERC20Upgradeable.sol

@@ -10,6 +10,20 @@ import {ERC20Upgradeable} from "@openzeppelin/contracts-upgradeable/token/ERC20/
  * @notice This contracts follows the standard ERC-20 Upgradeable model, but it cannot be transferred.
  */
 contract NonTransferableERC20Upgradeable is ERC20Upgradeable {
+    /**
+     * @dev By default, the standard ERC-20 `decimals` value is `18`. However, this value
+     * is overridden here to `9` to align with the number of decimal places used by
+     * the RLC token. This ensures consistency in how input values are handled
+     * when a voucher is minted.
+     *
+     * See https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/token/ERC20/ERC20.sol#L78
+     *
+     * @return The number of decimal places (9) used for token representation.
+     */
+    function decimals() public pure override returns (uint8) {
+        return 9;
+    }
+
     /**
      * @notice NonTransferableERC20Upgradeable is not transferable.
      */

contracts/VoucherHub.sol

@@ -103,6 +103,12 @@ contract VoucherHub is
         emit VoucherTypeCreated($._voucherTypes.length - 1, description, duration);
     }
 
+    /**
+     * This function only updates the duration for newly minted vouchers and not the existing ones to provide
+     * guarantees regarding the expiration of vouchers. When a voucher is delivered, its credits should not expire
+     * before the original expiration date.
+     * As mentioned in Halborn audit report (HAL-01), this is not a bug, but rather, an intended feature.
+     */
     function updateVoucherTypeDescription(
         uint256 id,
         string memory description

docs/VoucherHub.md

@@ -57,6 +57,11 @@ function createVoucherType(string description, uint256 duration) external
 function updateVoucherTypeDescription(uint256 id, string description) external
 ```
 
+This function only updates the duration for newly minted vouchers and not the existing ones to provide
+guarantees regarding the expiration of vouchers. When a voucher is delivered, its credits should not expire
+before the original expiration date.
+As mentioned in Halborn audit report (HAL-01), this is not a bug, but rather, an intended feature.
+
 ### updateVoucherTypeDuration
 
 ```solidity

test/VoucherHub.test.ts

@@ -1064,6 +1064,13 @@ describe('VoucherHub', function () {
                 'NonTransferableERC20Upgradeable: Unsupported transferFrom',
             );
         });
+
+        it('Should return 9 as the number of decimals', async function () {
+            const { voucherHub } = await loadFixture(deployFixture);
+
+            // Call the decimals function and check the returned value
+            expect(await voucherHub.decimals()).to.equal(9);
+        });
     });
 });