polkadot: pin one block per session (#1220)

* polkadot: propagate UnpinHandle to ActiveLeafUpdate

Also extract the leaf creation for tests
into a common function.

* dispute-coordinator: try pinned blocks for slashin

* apparently 1.72 is smarter than 1.70

* address nits

* rename fresh_leaf to new_leaf

polkadot/node/subsystem-test-helpers/src/mock.rs

@@ -16,12 +16,15 @@
 
 use std::sync::Arc;
 
+use polkadot_node_subsystem::{jaeger, ActivatedLeaf, LeafStatus};
+use sc_client_api::UnpinHandle;
 use sc_keystore::LocalKeystore;
+use sc_utils::mpsc::tracing_unbounded;
 use sp_application_crypto::AppCrypto;
 use sp_keyring::Sr25519Keyring;
 use sp_keystore::{Keystore, KeystorePtr};
 
-use polkadot_primitives::{AuthorityDiscoveryId, ValidatorId};
+use polkadot_primitives::{AuthorityDiscoveryId, Block, BlockNumber, Hash, ValidatorId};
 
 /// Get mock keystore with `Ferdie` key.
 pub fn make_ferdie_keystore() -> KeystorePtr {
@@ -40,3 +43,20 @@ pub fn make_ferdie_keystore() -> KeystorePtr {
 	.expect("Insert key into keystore");
 	keystore
 }
+
+/// Create a meaningless unpin handle for a block.
+pub fn dummy_unpin_handle(block: Hash) -> UnpinHandle<Block> {
+	let (dummy_sink, _) = tracing_unbounded("Expect Chaos", 69);
+	UnpinHandle::new(block, dummy_sink)
+}
+
+/// Create a new leaf with the given hash and number.
+pub fn new_leaf(hash: Hash, number: BlockNumber) -> ActivatedLeaf {
+	ActivatedLeaf {
+		hash,
+		number,
+		status: LeafStatus::Fresh,
+		unpin_handle: dummy_unpin_handle(hash),
+		span: Arc::new(jaeger::Span::Disabled),
+	}
+}