Do not run forced_canonicalization for archive nodes (#13051)

We don't canonicalize on archive nodes and thus `best_canonical` always returned `None`. So, the
moment such a node tried to force canonicalize, it was trapped in some endless loop.

This pr solves this by renaming `best_canonical` to `last_canonicalized` and also making the return
value more clear by introducing a custom enum `LastCanonicalized`.

substrate/client/state-db/src/lib.rs

@@ -283,6 +283,17 @@ fn to_meta_key<S: Codec>(suffix: &[u8], data: &S) -> Vec<u8> {
 	buffer
 }
 
+/// Status information about the last canonicalized block.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum LastCanonicalized {
+	/// Not yet have canonicalized any block.
+	None,
+	/// The given block number is the last canonicalized block.
+	Block(u64),
+	/// No canonicalization is happening (pruning mode is archive all).
+	NotCanonicalizing,
+}
+
 pub struct StateDbSync<BlockHash: Hash, Key: Hash, D: MetaDb> {
 	mode: PruningMode,
 	non_canonical: NonCanonicalOverlay<BlockHash, Key>,
@@ -349,15 +360,28 @@ impl<BlockHash: Hash, Key: Hash, D: MetaDb> StateDbSync<BlockHash, Key, D> {
 		Ok(commit)
 	}
 
-	fn best_canonical(&self) -> Option<u64> {
-		self.non_canonical.last_canonicalized_block_number()
+	/// Returns the block number of the last canonicalized block.
+	fn last_canonicalized(&self) -> LastCanonicalized {
+		if self.mode == PruningMode::ArchiveAll {
+			LastCanonicalized::NotCanonicalizing
+		} else {
+			self.non_canonical
+				.last_canonicalized_block_number()
+				.map(LastCanonicalized::Block)
+				.unwrap_or_else(|| LastCanonicalized::None)
+		}
 	}
 
 	fn is_pruned(&self, hash: &BlockHash, number: u64) -> IsPruned {
 		match self.mode {
 			PruningMode::ArchiveAll => IsPruned::NotPruned,
 			PruningMode::ArchiveCanonical | PruningMode::Constrained(_) => {
-				if self.best_canonical().map(|c| number > c).unwrap_or(true) {
+				if self
+					.non_canonical
+					.last_canonicalized_block_number()
+					.map(|c| number > c)
+					.unwrap_or(true)
+				{
 					if self.non_canonical.have_block(hash) {
 						IsPruned::NotPruned
 					} else {
@@ -611,9 +635,9 @@ impl<BlockHash: Hash, Key: Hash, D: MetaDb> StateDb<BlockHash, Key, D> {
 		self.db.write().remove(hash)
 	}
 
-	/// Returns last finalized block number.
-	pub fn best_canonical(&self) -> Option<u64> {
-		return self.db.read().best_canonical()
+	/// Returns last canonicalized block.
+	pub fn last_canonicalized(&self) -> LastCanonicalized {
+		self.db.read().last_canonicalized()
 	}
 
 	/// Check if block is pruned away.