srml: grandpa: Pause/resume current authority set (#3068)

* grandpa: add pause/resume signals to runtime module

* grandpa: add tests for srml pause/resume transitions

* node: bump spec_version

* Apply suggestions from code review

* Update core/finality-grandpa/primitives/src/lib.rs

* Update core/finality-grandpa/primitives/src/lib.rs

substrate/core/finality-grandpa/primitives/src/lib.rs

@@ -93,6 +93,14 @@ pub enum ConsensusLog<N: Codec> {
 	/// Note that the authority with given index is disabled until the next change.
 	#[codec(index = "3")]
 	OnDisabled(AuthorityIndex),
+	/// A signal to pause the current authority set after the given delay.
+	/// After finalizing the block at _delay_ the authorities should stop voting.
+	#[codec(index = "4")]
+	Pause(N),
+	/// A signal to resume the current authority set after the given delay.
+	/// After authoring the block at _delay_ the authorities should resume voting.
+	#[codec(index = "5")]
+	Resume(N),
 }
 
 impl<N: Codec> ConsensusLog<N> {
@@ -100,7 +108,7 @@ impl<N: Codec> ConsensusLog<N> {
 	pub fn try_into_change(self) -> Option<ScheduledChange<N>> {
 		match self {
 			ConsensusLog::ScheduledChange(change) => Some(change),
-			ConsensusLog::ForcedChange(_, _) | ConsensusLog::OnDisabled(_) => None,
+			_ => None,
 		}
 	}
 
@@ -108,7 +116,23 @@ impl<N: Codec> ConsensusLog<N> {
 	pub fn try_into_forced_change(self) -> Option<(N, ScheduledChange<N>)> {
 		match self {
 			ConsensusLog::ForcedChange(median, change) => Some((median, change)),
-			ConsensusLog::ScheduledChange(_) | ConsensusLog::OnDisabled(_) => None,
+			_ => None,
+		}
+	}
+
+	/// Try to cast the log entry as a contained pause signal.
+	pub fn try_into_pause(self) -> Option<N> {
+		match self {
+			ConsensusLog::Pause(delay) => Some(delay),
+			_ => None,
+		}
+	}
+
+	/// Try to cast the log entry as a contained resume signal.
+	pub fn try_into_resume(self) -> Option<N> {
+		match self {
+			ConsensusLog::Resume(delay) => Some(delay),
+			_ => None,
 		}
 	}
 }