Add missing docs to sr-primitives. (#1531)

substrate/core/sr-primitives/src/generic/digest.rs

@@ -23,9 +23,11 @@ use traits::{self, Member, DigestItem as DigestItemT, MaybeHash};
 
 use substrate_primitives::hash::H512 as Signature;
 
+/// Generic header digest.
 #[derive(PartialEq, Eq, Clone, Encode, Decode)]
 #[cfg_attr(feature = "std", derive(Debug, Serialize))]
 pub struct Digest<Item> {
+	/// A list of logs in the digest.
 	pub logs: Vec<Item>,
 }
 
@@ -175,6 +177,7 @@ impl<Hash: Decode, AuthorityId: Decode> Decode for DigestItem<Hash, AuthorityId>
 }
 
 impl<'a, Hash: Codec + Member, AuthorityId: Codec + Member> DigestItemRef<'a, Hash, AuthorityId> {
+	/// Cast this digest item into `AuthoritiesChange`.
 	pub fn as_authorities_change(&self) -> Option<&'a [AuthorityId]> {
 		match *self {
 			DigestItemRef::AuthoritiesChange(ref authorities) => Some(authorities),
@@ -182,6 +185,7 @@ impl<'a, Hash: Codec + Member, AuthorityId: Codec + Member> DigestItemRef<'a, Ha
 		}
 	}
 
+	/// Cast this digest item into `ChangesTrieRoot`.
 	pub fn as_changes_trie_root(&self) -> Option<&'a Hash> {
 		match *self {
 			DigestItemRef::ChangesTrieRoot(ref changes_trie_root) => Some(changes_trie_root),