From f02b3a84728bc913da6d5b0c1898d0fc8faa2dc5 Mon Sep 17 00:00:00 2001
From: Tobin Harding <me@tobin.cc>
Date: Wed, 9 Mar 2022 12:49:41 +1100
Subject: [PATCH] Add code comment for emtpy input

The line of code `let mut have_witness = self.input.is_empty();` is
puzzling if one does not know _why_ we serialize in BIP141 style when
there are no inputs.

Add a code comment to save devs spending time trying to work out _why_
this is correct.
---
 src/blockdata/transaction.rs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/blockdata/transaction.rs b/src/blockdata/transaction.rs
index fcb3f022..e3c9b1f7 100644
--- a/src/blockdata/transaction.rs
+++ b/src/blockdata/transaction.rs
@@ -588,6 +588,8 @@ impl Encodable for Transaction {
     ) -> Result<usize, io::Error> {
         let mut len = 0;
         len += self.version.consensus_encode(&mut s)?;
+        // To avoid serialization ambiguity, no inputs means we use BIP141 serialization (see
+        // `Transaction` docs for full explanation).
         let mut have_witness = self.input.is_empty();
         for input in &self.input {
             if !input.witness.is_empty() {