Make minimum validator count dynamic.

demo/cli/src/lib.rs

@@ -144,6 +144,7 @@ pub fn run<I, T>(args: I) -> error::Result<()> where
 			existential_deposit: 500,
 			balances: vec![(god_key.clone().into(), 1u64 << 63)].into_iter().collect(),
 			validator_count: 12,
+			minimum_validator_count: 4,
 			sessions_per_era: 24,	// 24 hours per era.
 			bonding_duration: 90,	// 90 days per bond.
 			early_era_slash: 10000,

demo/executor/src/lib.rs

@@ -199,6 +199,7 @@ mod tests {
 				balances: vec![(alice(), 111)],
 				intentions: vec![alice(), bob(), Charlie.to_raw_public().into()],
 				validator_count: 3,
+				minimum_validator_count: 0,
 				bonding_duration: 0,
 				transaction_base_fee: 1,
 				transaction_byte_fee: 0,

substrate/runtime/contract/src/tests.rs

@@ -100,6 +100,7 @@ fn new_test_ext(existential_deposit: u64, gas_price: u64) -> runtime_io::TestExt
 			balances: vec![],
 			intentions: vec![],
 			validator_count: 2,
+			minimum_validator_count: 0,
 			bonding_duration: 0,
 			transaction_base_fee: 0,
 			transaction_byte_fee: 0,

substrate/runtime/council/src/lib.rs

@@ -688,6 +688,7 @@ mod tests {
 			balances: vec![(1, 10), (2, 20), (3, 30), (4, 40), (5, 50), (6, 60)],
 			intentions: vec![],
 			validator_count: 2,
+			minimum_validator_count: 0,
 			bonding_duration: 0,
 			transaction_base_fee: 0,
 			transaction_byte_fee: 0,

substrate/runtime/democracy/src/lib.rs

@@ -429,6 +429,7 @@ mod tests {
 			balances: vec![(1, 10), (2, 20), (3, 30), (4, 40), (5, 50), (6, 60)],
 			intentions: vec![],
 			validator_count: 2,
+			minimum_validator_count: 0,
 			bonding_duration: 3,
 			transaction_base_fee: 0,
 			transaction_byte_fee: 0,

substrate/runtime/executive/src/lib.rs

@@ -278,6 +278,7 @@ mod tests {
 			balances: vec![(1, 111)],
 			intentions: vec![],
 			validator_count: 0,
+			minimum_validator_count: 0,
 			bonding_duration: 0,
 			transaction_base_fee: 10,
 			transaction_byte_fee: 0,

substrate/runtime/staking/src/genesis_config.rs

@@ -39,7 +39,8 @@ pub struct GenesisConfig<T: Trait> {
 	pub current_era: T::BlockNumber,
 	pub balances: Vec<(T::AccountId, T::Balance)>,
 	pub intentions: Vec<T::AccountId>,
-	pub validator_count: u64,
+	pub validator_count: u32,
+	pub minimum_validator_count: u32,
 	pub bonding_duration: T::BlockNumber,
 	pub transaction_base_fee: T::Balance,
 	pub transaction_byte_fee: T::Balance,
@@ -60,6 +61,7 @@ impl<T: Trait> GenesisConfig<T> where T::AccountId: From<u64> {
 			balances: vec![(T::AccountId::from(1), T::Balance::sa(111))],
 			intentions: vec![T::AccountId::from(1), T::AccountId::from(2), T::AccountId::from(3)],
 			validator_count: 3,
+			minimum_validator_count: 1,
 			bonding_duration: T::BlockNumber::sa(0),
 			transaction_base_fee: T::Balance::sa(0),
 			transaction_byte_fee: T::Balance::sa(0),
@@ -88,6 +90,7 @@ impl<T: Trait> GenesisConfig<T> where T::AccountId: From<u64> {
 			],
 			intentions: vec![T::AccountId::from(1), T::AccountId::from(2), T::AccountId::from(3)],
 			validator_count: 3,
+			minimum_validator_count: 1,
 			bonding_duration: T::BlockNumber::sa(0),
 			transaction_base_fee: T::Balance::sa(1),
 			transaction_byte_fee: T::Balance::sa(0),
@@ -110,6 +113,7 @@ impl<T: Trait> Default for GenesisConfig<T> {
 			balances: vec![],
 			intentions: vec![],
 			validator_count: 0,
+			minimum_validator_count: 0,
 			bonding_duration: T::BlockNumber::sa(1000),
 			transaction_base_fee: T::Balance::sa(0),
 			transaction_byte_fee: T::Balance::sa(0),
@@ -133,6 +137,7 @@ impl<T: Trait> primitives::BuildStorage for GenesisConfig<T> {
 			Self::hash(<Intentions<T>>::key()).to_vec() => self.intentions.encode(),
 			Self::hash(<SessionsPerEra<T>>::key()).to_vec() => self.sessions_per_era.encode(),
 			Self::hash(<ValidatorCount<T>>::key()).to_vec() => self.validator_count.encode(),
+			Self::hash(<MinimumValidatorCount<T>>::key()).to_vec() => self.minimum_validator_count.encode(),
 			Self::hash(<BondingDuration<T>>::key()).to_vec() => self.bonding_duration.encode(),
 			Self::hash(<TransactionBaseFee<T>>::key()).to_vec() => self.transaction_base_fee.encode(),
 			Self::hash(<TransactionByteFee<T>>::key()).to_vec() => self.transaction_byte_fee.encode(),

substrate/runtime/staking/src/lib.rs

@@ -64,7 +64,7 @@ mod genesis_config;
 #[cfg(feature = "std")]
 pub use genesis_config::GenesisConfig;
 
-const MINIMUM_REQUIRED_VALIDATORS: usize = 4;
+const DEFAULT_MINIMUM_VALIDATOR_COUNT: usize = 4;
 
 /// Number of account IDs stored per enum set.
 const ENUM_SET_SIZE: usize = 64;
@@ -175,8 +175,10 @@ decl_storage! {
 
 	// The length of the bonding duration in eras.
 	pub BondingDuration get(bonding_duration): b"sta:loc" => required T::BlockNumber;
-	// The length of a staking era in sessions.
+	// The ideal number of staking participants.
 	pub ValidatorCount get(validator_count): b"sta:vac" => required u32;
+	// Minimum number of staking participants before emergency conditions are imposed.
+	pub MinimumValidatorCount: b"sta:minimum_validator_count" => u32;
 	// The length of a staking era in sessions.
 	pub SessionsPerEra get(sessions_per_era): b"sta:spe" => required T::BlockNumber;
 	// The total amount of stake on the system.
@@ -280,6 +282,10 @@ impl<T: Trait> Module<T> {
 
 	// PUBLIC IMMUTABLES
 
+	pub fn minimum_validator_count() -> usize {
+		<MinimumValidatorCount<T>>::get().map(|v| v as usize).unwrap_or(DEFAULT_MINIMUM_VALIDATOR_COUNT)
+	}
+
 	/// The length of a staking era in blocks.
 	pub fn era_length() -> T::BlockNumber {
 		Self::sessions_per_era() * <session::Module<T>>::length()
@@ -403,7 +409,7 @@ impl<T: Trait> Module<T> {
 	/// Effects will be felt at the beginning of the next era.
 	fn unstake(aux: &T::PublicAux, intentions_index: u32) -> Result {
 		// unstake fails in degenerate case of having too few existing staked parties
-		if Self::intentions().len() <= MINIMUM_REQUIRED_VALIDATORS {
+		if Self::intentions().len() <= Self::minimum_validator_count() {
 			return Err("cannot unstake when there are too few staked participants")
 		}
 		Self::apply_unstake(aux.ref_into(), intentions_index as usize)
@@ -742,7 +748,7 @@ impl<T: Trait> Module<T> {
 	fn slash_validator(v: &T::AccountId, slash: T::Balance) {
 		// skip the slash in degenerate case of having only 4 staking participants despite having a larger
 		// desired number of validators (validator_count).
-		if Self::intentions().len() <= MINIMUM_REQUIRED_VALIDATORS {
+		if Self::intentions().len() <= Self::minimum_validator_count() {
 			return
 		}
 
@@ -840,7 +846,7 @@ impl<T: Trait> Module<T> {
 			.collect::<Vec<_>>();
 
 		// Avoid making new era if it would leave us with fewer than the minimum needed validators
-		if intentions.len() < MINIMUM_REQUIRED_VALIDATORS {
+		if intentions.len() < Self::minimum_validator_count() {
 			return
 		}
 

substrate/runtime/staking/src/mock.rs

@@ -89,6 +89,7 @@ pub fn new_test_ext(ext_deposit: u64, session_length: u64, sessions_per_era: u64
 		},
 		intentions: vec![],
 		validator_count: 2,
+		minimum_validator_count: 0,
 		bonding_duration: 3,
 		transaction_base_fee: 0,
 		transaction_byte_fee: 0,