refactor!: unify the two _transfer implementations

contracts/abstract/IexecEscrow.sol

@@ -61,17 +61,17 @@ abstract contract IexecEscrow is FacetBase, IexecERC20Events, IexecEscrowEvents
     /**
      * Transfer value from a spender account to a receiver account.
      * @notice
-     * This function does not check for self-transfers
-     * because its current usage does not require such verification.
-     * Indeed, all operations that use this function are always between
-     * the proxy contract and another actor of the platform (requester,
-     * owner of dataset/application/workerpool).
+     * This is the single implementation of a balance move over `m_balances`.
+     * It backs both the escrow operations of this contract (lock, unlock,
+     * reward) and the ERC-20 entry points of the escrow facet.
+     *
+     * A self-transfer is a no-op on the balances and is not rejected.
      *
      * @param from The address of the spender account.
      * @param to The address of the receiver account.
      * @param value The value to transfer.
      */
-    function _transfer(address from, address to, uint256 value) private {
+    function _transfer(address from, address to, uint256 value) internal {
         require(from != address(0), "IexecEscrow: Transfer from empty address");
         require(to != address(0), "IexecEscrow: Transfer to empty address");
         PocoStorageLib.PocoStorage storage $ = PocoStorageLib.getPocoStorage();

contracts/facets/IexecEscrowTokenFacet.sol

@@ -4,14 +4,21 @@
 pragma solidity ^0.8.0;
 
 import {FacetBase} from "../abstract/FacetBase.sol";
+import {IexecEscrow} from "../abstract/IexecEscrow.sol";
 import {IexecERC20} from "../interfaces/IexecERC20.sol";
 import {IexecEscrowToken} from "../interfaces/IexecEscrowToken.sol";
 import {IexecTokenSpender} from "../interfaces/IexecTokenSpender.sol";
 import {IexecPoco1} from "../interfaces/IexecPoco1.sol";
 import {IexecLibOrders_v5} from "../libs/IexecLibOrders_v5.sol";
 import {PocoStorageLib} from "../libs/PocoStorageLib.sol";
 
-contract IexecEscrowTokenFacet is IexecEscrowToken, IexecTokenSpender, IexecERC20, FacetBase {
+contract IexecEscrowTokenFacet is
+    FacetBase,
+    IexecERC20,
+    IexecTokenSpender,
+    IexecEscrowToken,
+    IexecEscrow
+{
     /***************************************************************************
      *                         Escrow methods: public                          *
      ***************************************************************************/
@@ -272,25 +279,6 @@ contract IexecEscrowTokenFacet is IexecEscrowToken, IexecTokenSpender, IexecERC2
         return true;
     }
 
-    function _transferUnchecked(address sender, address recipient, uint256 amount) internal {
-        require(sender != address(0), "ERC20: transfer from the zero address");
-        require(recipient != address(0), "ERC20: transfer to the zero address");
-        PocoStorageLib.PocoStorage storage $ = PocoStorageLib.getPocoStorage();
-        uint256 senderBalance = $.m_balances[sender];
-        // TEMPORARY MIGRATION FIX: Check balance to prevent underflow and revert without reason for backward compatibility
-        // TODO: Remove this in the next major version
-        if (senderBalance < amount) {
-            revert();
-        }
-        $.m_balances[sender] = senderBalance - amount;
-        $.m_balances[recipient] = $.m_balances[recipient] + amount;
-        emit Transfer(sender, recipient, amount);
-    }
-
-    function _transfer(address sender, address recipient, uint256 amount) internal {
-        _transferUnchecked(sender, recipient, amount);
-    }
-
     function _mint(address account, uint256 amount) internal {
         require(account != address(0), "ERC20: mint to the zero address");
         PocoStorageLib.PocoStorage storage $ = PocoStorageLib.getPocoStorage();