From 699dfcd8ad9487a4e04c1ffc68211e84e126b3d2 Mon Sep 17 00:00:00 2001
From: Andrew Chow <achow101-github@achow101.com>
Date: Fri, 4 Jun 2021 16:40:48 -0400
Subject: [PATCH] Opportunistically use bech32m change addresses if available

If a transaction as a segwit output, use a bech32m change address if
they are available. If not, fallback to bech32. If bech32 change
addresses are unavailable, fallback to the default address type.
---
 src/wallet/wallet.cpp | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index fbda77ed62c..0f693026971 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -1909,7 +1909,13 @@ OutputType CWallet::TransactionChangeType(const std::optional<OutputType>& chang
         int witnessversion = 0;
         std::vector<unsigned char> witnessprogram;
         if (recipient.scriptPubKey.IsWitnessProgram(witnessversion, witnessprogram)) {
-            return OutputType::BECH32;
+            if (GetScriptPubKeyMan(OutputType::BECH32M, true)) {
+                return OutputType::BECH32M;
+            } else if (GetScriptPubKeyMan(OutputType::BECH32, true)) {
+                return OutputType::BECH32;
+            } else {
+                return m_default_address_type;
+            }
         }
     }