closes https://github.com/paritytech/polkadot-sdk/issues/158.
partially addresses
https://github.com/paritytech/polkadot-sdk/issues/226.
Instead of fragile calculation of current balance by looking at `free
balance - ED`, Nomination Pool now freezes ED in the pool reward account
to restrict an account from going below minimum balance. This also has a
nice side effect that if ED changes, we know how much is the imbalance
in ED frozen in the pool and the current required ED. A pool operator
can diligently top up the pool with the deficit in ED or vice versa,
withdraw the excess they transferred to the pool.
## Notable changes
- New call `adjust_pool_deposit`: Allows to top up the deficit or
withdraw the excess deposited funds to the pool.
- Uses Fungible trait (instead of Currency trait). Since NP was not
doing any locking/reserving previously, no migration is needed for this.
- One time migration of freezing ED from each of the existing pools (not
very PoV friendly but fine for relay chain).
The FRAME development environment provides modules (called "pallets") and support libraries that you can use, modify,
and extend to build the runtime logic to suit the needs of your blockchain.
Ankan
f820dc0a1f