Ensure that unvested coins can be staked

[tonimateos]

As a token owner with cliff and/or vesting I want to be able to stake on the network my unvested coins

• initial state: 10 vested already, 1000 locked because of vesting
  you want to put 500 into staking
• final state: X frozen, Y vested already, Z locked because of vesting

ACCEPTANCE:

• I can stake my unvested coins
• I understand the final state in the case mentioned above

[ghost]

Before:

Join as a delegator:

Final state:

[ghost]

• staking pallet uses freeze to lock funds of participants
• vesting pallet uses lock to lock funds of participants

both freeze and lock operations are treated same and sometimes used interchangeably, this means that funds may "overlap". But even if the whole funds are unvested i.e unlocked, they are not converted to free balance since there is still a freeze on funds that are used for staking. So usable balance will never include locked or frozen funds unless there is some mechanism locking/freezing it

So, basically, this suffices to can locked funds be frozen?, and the answer is - yes!

Example:

Alice starts with 1 free and 9 unvested units, which is basically a freeze/lock on 9 units. Then she stakes 9 units, which places another lock on the same 9 units. And for 9 units to be totally "free" it needs to "escape" two locks:

• 9 units should be fully vested
• 9 units should be unstaked

[ghost]

more info here paritytech/polkadot-sdk#236 (comment)