From b3cf97940cca0995d59d191204b7efd556264d52 Mon Sep 17 00:00:00 2001
From: Robert Habermeier <rphmeier@gmail.com>
Date: Wed, 12 Feb 2020 13:15:49 +0100
Subject: [PATCH] add some more docs on PreRuntime digests (#4896)
---
substrate/primitives/runtime/src/generic/digest.rs | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/substrate/primitives/runtime/src/generic/digest.rs b/substrate/primitives/runtime/src/generic/digest.rs
index 4d09b587932..9d4fbe48d55 100644
--- a/substrate/primitives/runtime/src/generic/digest.rs
+++ b/substrate/primitives/runtime/src/generic/digest.rs
@@ -87,6 +87,12 @@ pub enum DigestItem<Hash> {
/// the consensus engine can (and should) read them itself to avoid
/// code and state duplication. It is erroneous for a runtime to produce
/// these, but this is not (yet) checked.
+ ///
+ /// NOTE: the runtime is not allowed to panic or fail in an `on_initialize`
+ /// call if an expected `PreRuntime` digest is not present. It is the
+ /// responsibility of a external block verifier to check this. Runtime API calls
+ /// will initialize the block without pre-runtime digests, so initialization
+ /// cannot fail when they are missing.
PreRuntime(ConsensusEngineId, Vec<u8>),
/// A message from the runtime to the consensus engine. This should *never*
--
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