grandpa: don't send equivocation reports for local identities (#7372)

* grandpa: don't send equivocation reports for local identities

* grandpa: add test for self-report

* grandpa: fix test compilation

this works on rust nightly but breaks on ci which is using rust stable

substrate/client/finality-grandpa/src/tests.rs

@@ -1813,3 +1813,49 @@ fn imports_justification_for_regular_blocks_on_import() {
 		client.justification(&BlockId::Hash(block_hash)).unwrap().is_some(),
 	);
 }
+
+#[test]
+fn grandpa_environment_doesnt_send_equivocation_reports_for_itself() {
+	let alice = Ed25519Keyring::Alice;
+	let voters = make_ids(&[alice]);
+
+	let environment = {
+		let mut net = GrandpaTestNet::new(TestApi::new(voters), 1);
+		let peer = net.peer(0);
+		let network_service = peer.network_service().clone();
+		let link = peer.data.lock().take().unwrap();
+		let (keystore, _keystore_path) = create_keystore(alice);
+		test_environment(&link, Some(keystore), network_service.clone(), ())
+	};
+
+	let signed_prevote = {
+		let prevote = finality_grandpa::Prevote {
+			target_hash: H256::random(),
+			target_number: 1,
+		};
+
+		let signed = alice.sign(&[]).into();
+		(prevote, signed)
+	};
+
+	let mut equivocation = finality_grandpa::Equivocation {
+		round_number: 1,
+		identity: alice.public().into(),
+		first: signed_prevote.clone(),
+		second: signed_prevote.clone(),
+	};
+
+	// reporting the equivocation should fail since the offender is a local
+	// authority (i.e. we have keys in our keystore for the given id)
+	let equivocation_proof = sp_finality_grandpa::Equivocation::Prevote(equivocation.clone());
+	assert!(matches!(
+		environment.report_equivocation(equivocation_proof),
+		Err(Error::Safety(_))
+	));
+
+	// if we set the equivocation offender to another id for which we don't have
+	// keys it should work
+	equivocation.identity = Default::default();
+	let equivocation_proof = sp_finality_grandpa::Equivocation::Prevote(equivocation);
+	assert!(environment.report_equivocation(equivocation_proof).is_ok());
+}