From 518348b88df8817fdf69820a27aa9aa5ff315b59 Mon Sep 17 00:00:00 2001
From: Joshy Orndorff <JoshOrndorff@users.noreply.github.com>
Date: Tue, 2 Jun 2020 09:21:12 -0400
Subject: [PATCH] impl FindAuthor<T::AuthorityId> for Aura (#6205)
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* Something compiles

* compiles _and_ maintains old version

* Comments

* try to pass CI

* Update frame/aura/src/lib.rs

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

* Update frame/aura/src/lib.rs

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>
---
 substrate/frame/aura/src/lib.rs | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/substrate/frame/aura/src/lib.rs b/substrate/frame/aura/src/lib.rs
index d124ef0017..ca3d1f15f4 100644
--- a/substrate/frame/aura/src/lib.rs
+++ b/substrate/frame/aura/src/lib.rs
@@ -162,6 +162,27 @@ impl<T: Trait> FindAuthor<u32> for Module<T> {
 	}
 }
 
+/// We can not implement `FindAuthor` twice, because the compiler does not know if 
+/// `u32 == T::AuthorityId` and thus, prevents us to implement the trait twice.
+#[doc(hidden)]
+pub struct FindAccountFromAuthorIndex<T, Inner>(sp_std::marker::PhantomData<(T, Inner)>);
+
+impl<T: Trait, Inner: FindAuthor<u32>> FindAuthor<T::AuthorityId>
+	for FindAccountFromAuthorIndex<T, Inner>
+{
+	fn find_author<'a, I>(digests: I) -> Option<T::AuthorityId>
+		where I: 'a + IntoIterator<Item=(ConsensusEngineId, &'a [u8])>
+	{
+		let i = Inner::find_author(digests)?;
+
+		let validators = <Module<T>>::authorities();
+		validators.get(i as usize).map(|k| k.clone())
+	}
+}
+
+/// Find the authority ID of the Aura authority who authored the current block.
+pub type AuraAuthorId<T> = FindAccountFromAuthorIndex<T, Module<T>>;
+
 impl<T: Trait> IsMember<T::AuthorityId> for Module<T> {
 	fn is_member(authority_id: &T::AuthorityId) -> bool {
 		Self::authorities()