block_header can fail so return Result (#8581)

* block_header can fail so return Result

* Restore previous return type based on feedback

* Fix failing doc tests running on non-code

rpc/src/v1/impls/light/parity.rs

@@ -395,9 +395,9 @@ impl Parity for ParityClient {
 
 		let engine = self.light_dispatch.client.engine().clone();
 		let from_encoded = move |encoded: encoded::Header| {
-			let header = encoded.decode().expect("decoding error"); // REVIEW: not sure what to do here; what is a decent return value for the error case here?
+			let header = encoded.decode().map_err(errors::decode)?;
 			let extra_info = engine.extra_info(&header);
-			RichHeader {
+			Ok(RichHeader {
 				inner: Header {
 					hash: Some(header.hash().into()),
 					size: Some(encoded.rlp().as_raw().len().into()),
@@ -418,9 +418,8 @@ impl Parity for ParityClient {
 					extra_data: Bytes::new(header.extra_data().clone()),
 				},
 				extra_info: extra_info,
-			}
+			})
 		};
-
 		// Note: Here we treat `Pending` as `Latest`.
 		//       Since light clients don't produce pending blocks
 		//       (they don't have state) we can safely fallback to `Latest`.
@@ -430,7 +429,7 @@ impl Parity for ParityClient {
 			BlockNumber::Latest | BlockNumber::Pending => BlockId::Latest,
 		};
 
-		Box::new(self.fetcher().header(id).map(from_encoded))
+		Box::new(self.fetcher().header(id).and_then(from_encoded))
 	}
 
 	fn ipfs_cid(&self, content: Bytes) -> Result<String> {

util/journaldb/src/earlymergedb.rs

@@ -57,7 +57,7 @@ enum RemoveFrom {
 /// the removals actually take effect.
 ///
 /// journal format:
-/// ```
+/// ```text
 /// [era, 0] => [ id, [insert_0, ...], [remove_0, ...] ]
 /// [era, 1] => [ id, [insert_0, ...], [remove_0, ...] ]
 /// [era, n] => [ ... ]
@@ -76,7 +76,7 @@ enum RemoveFrom {
 /// which includes an original key, if any.
 ///
 /// The semantics of the `counter` are:
-/// ```
+/// ```text
 /// insert key k:
 ///   counter already contains k: count += 1
 ///   counter doesn't contain k:
@@ -92,7 +92,7 @@ enum RemoveFrom {
 ///
 /// Practically, this means that for each commit block turning from recent to ancient we do the
 /// following:
-/// ```
+/// ```text
 /// is_canonical:
 ///   inserts: Ignored (left alone in the backing database).
 ///   deletes: Enacted; however, recent history queue is checked for ongoing references. This is

util/journaldb/src/refcounteddb.rs

@@ -40,7 +40,7 @@ use util::{DatabaseKey, DatabaseValueView, DatabaseValueRef};
 /// the removals actually take effect.
 ///
 /// journal format:
-/// ```
+/// ```text
 /// [era, 0] => [ id, [insert_0, ...], [remove_0, ...] ]
 /// [era, 1] => [ id, [insert_0, ...], [remove_0, ...] ]
 /// [era, n] => [ ... ]