Configurable maximum validators (#2586)

* guide: max_validators

* guide: new approach

* restrict validators based on configurable max

* add some tests

* fix wasm build (Vec)

* clean up warnings

* add logging

* set validator indices in tests as well

* fix common tests

* Update runtime/parachains/src/util.rs

Co-authored-by: Andronik Ordian <write@reusable.software>

Co-authored-by: Andronik Ordian <write@reusable.software>

polkadot/runtime/parachains/src/session_info.rs

@@ -24,12 +24,14 @@ use frame_support::{
 	decl_storage, decl_module, decl_error,
 	traits::OneSessionHandler, weights::Weight,
 };
-use crate::{configuration, paras, scheduler};
+use crate::{configuration, paras, scheduler, shared};
+use crate::util::take_active_subset;
 use sp_std::vec::Vec;
 
 pub trait Config:
 	frame_system::Config
 	+ configuration::Config
+	+ shared::Config
 	+ paras::Config
 	+ scheduler::Config
 	+ AuthorityDiscoveryConfig
@@ -88,6 +90,8 @@ impl<T: Config> Module<T> {
 		let validators = notification.validators.clone();
 		let discovery_keys = <T as AuthorityDiscoveryConfig>::authorities();
 		let assignment_keys = AssignmentKeysUnsafe::get();
+
+		let active_set = <shared::Module<T>>::active_validator_indices();
 		let validator_groups = <scheduler::Module<T>>::validator_groups();
 		let n_cores = n_parachains + config.parathread_cores;
 		let zeroth_delay_tranche_width = config.zeroth_delay_tranche_width;
@@ -114,9 +118,9 @@ impl<T: Config> Module<T> {
 		}
 		// create a new entry in `Sessions` with information about the current session
 		let new_session_info = SessionInfo {
-			validators,
-			discovery_keys,
-			assignment_keys,
+			validators: take_active_subset(&active_set, &validators),
+			discovery_keys: take_active_subset(&active_set, &discovery_keys),
+			assignment_keys: take_active_subset(&active_set, &assignment_keys),
 			validator_groups,
 			n_cores,
 			zeroth_delay_tranche_width,
@@ -186,11 +190,14 @@ mod tests {
 
 			if let Some(notification) = new_session(b + 1) {
 				Configuration::initializer_on_new_session(
-					&notification.validators,
-					&notification.queued,
 					&notification.session_index,
 				);
-				Shared::initializer_on_new_session(&notification);
+				Shared::initializer_on_new_session(
+					notification.session_index,
+					notification.random_seed,
+					&notification.new_config,
+					notification.validators.clone(),
+				);
 				SessionInfo::initializer_on_new_session(&notification);
 			}