According to the IAS 37, since there is no present obligation provision for future losses can not be done.
But according to IFRS 15, when calculating revenue from the contract over the period of time firstly we calculating the overall profit or loss from the contract. if there is a loss from the contract that loss will be identify in the current year and will show it as provision for loss in contract.
The key difference is that in IFRS15 there is a contract, so creating the obligation. With future operating losses there is no contract and so no obligation.