Ban ED of zero unless feature enabled

frame/balances/Cargo.toml

@@ -39,5 +39,6 @@ std = [
 	"sp-runtime/std",
 	"sp-std/std",
 ]
+zero_ed = []
 runtime-benchmarks = ["frame-benchmarking/runtime-benchmarks"]
 try-runtime = ["frame-support/try-runtime"]

frame/balances/src/lib.rs

@@ -202,6 +202,14 @@ const LOG_TARGET: &str = "runtime::balances";
 
 type AccountIdLookupOf<T> = <<T as frame_system::Config>::Lookup as StaticLookup>::Source;
 
+#[cfg(feature = "zero_ed")]
+fn assert_valid_ed<Balance: Zero>(_: Balance) {}
+
+#[cfg(not(feature = "zero_ed"))]
+fn assert_valid_ed<Balance: Zero>(existential_deposit: Balance) {
+	assert!(!existential_deposit.is_zero(), "The existential deposit must be greater than zero!");
+}
+
 #[frame_support::pallet]
 pub mod pallet {
 	use super::*;
@@ -452,12 +460,14 @@ pub mod pallet {
 	#[pallet::genesis_build]
 	impl<T: Config<I>, I: 'static> GenesisBuild<T, I> for GenesisConfig<T, I> {
 		fn build(&self) {
+			let ed = <T as Config<I>>::ExistentialDeposit::get();
+			assert_valid_ed(ed);
 			let total = self.balances.iter().fold(Zero::zero(), |acc: T::Balance, &(_, n)| acc + n);
 			<TotalIssuance<T, I>>::put(total);
 
 			for (_, balance) in &self.balances {
 				assert!(
-					*balance >= <T as Config<I>>::ExistentialDeposit::get(),
+					*balance >= ed,
 					"the balance of any account should always be at least the existential deposit.",
 				)
 			}

frame/balances/src/tests/currency_tests.rs

@@ -974,7 +974,7 @@ fn slash_reserved_on_non_existant_works() {
 fn operations_on_dead_account_should_not_change_state() {
 	// These functions all use `mutate_account` which may introduce a storage change when
 	// the account never existed to begin with, and shouldn't exist in the end.
-	ExtBuilder::default().existential_deposit(0).build_and_execute_with(|| {
+	ExtBuilder::default().existential_deposit(1).build_and_execute_with(|| {
 		assert!(!frame_system::Account::<Test>::contains_key(&1337));
 
 		// Unreserve
@@ -993,6 +993,14 @@ fn operations_on_dead_account_should_not_change_state() {
 	});
 }
 
+#[test]
+#[should_panic = "The existential deposit must be greater than zero!"]
+fn zero_ed_is_prohibited() {
+	// These functions all use `mutate_account` which may introduce a storage change when
+	// the account never existed to begin with, and shouldn't exist in the end.
+	ExtBuilder::default().existential_deposit(0).build_and_execute_with(|| {});
+}
+
 #[test]
 fn named_reserve_should_work() {
 	ExtBuilder::default().build_and_execute_with(|| {