Merge #19396: refactor: Remove confusing OutputType::CHANGE_AUTO

fa927ff884ae373c676deed63180a8d238872cdc Enable Wswitch for OutputType (MarcoFalke)
faddad71f648ed99734f4f8811bd4bc7232ca670 Remove confusing OutputType::CHANGE_AUTO (MarcoFalke)
fa2eb383522249a5f4d48726c520cec5de496614 interfaces: Remove unused getDefaultChangeType (MarcoFalke)

Pull request description:

  `OutputType::CHANGE_AUTO` is problematic for several reasons:

  * An output that is not change must never be described by `CHANGE_AUTO`. Simply allowing that option makes the code confusing and review harder than it needs to be.
  * To make review even harder, `CHANGE_AUTO` requires `-Wswitch` to be disabled for `OutputType`

  Fix both issues by removing `CHANGE_AUTO` and then enabling `-Wswitch` for `OutputType`

ACKs for top commit:
  promag:
    Code review ACK fa927ff884ae373c676deed63180a8d238872cdc.
  laanwj:
    Code review ACK fa927ff884ae373c676deed63180a8d238872cdc

Tree-SHA512: 24fd809757aa343866c94dafe9a7130b50cda4f77c97666d407f99b813f75b115a7d8e688a6bc2a737e87cba64ddd4e43f2b3c5538fd35fabb5845807bb39134

1 files changed, 8 insertions, 5 deletions

diff --git a/src/wallet/wallet.h b/src/wallet/wallet.h
index 82bb079110..32d8481cd8 100644
--- a/src/wallet/wallet.h
+++ b/src/wallet/wallet.h
@@ -105,9 +105,6 @@ class ReserveDestination;
 //! Default for -addresstype
 constexpr OutputType DEFAULT_ADDRESS_TYPE{OutputType::BECH32};
 
-//! Default for -changetype
-constexpr OutputType DEFAULT_CHANGE_TYPE{OutputType::CHANGE_AUTO};
-
 static constexpr uint64_t KNOWN_WALLET_FLAGS =
         WALLET_FLAG_AVOID_REUSE
     |   WALLET_FLAG_BLANK_WALLET
@@ -934,7 +931,7 @@ public:
     Balance GetBalance(int min_depth = 0, bool avoid_reuse = true) const;
     CAmount GetAvailableBalance(const CCoinControl* coinControl = nullptr) const;
 
-    OutputType TransactionChangeType(OutputType change_type, const std::vector<CRecipient>& vecSend);
+    OutputType TransactionChangeType(const Optional<OutputType>& change_type, const std::vector<CRecipient>& vecSend);
 
     /**
      * Insert additional inputs into the transaction by
@@ -1012,7 +1009,13 @@ public:
     CFeeRate m_fallback_fee{DEFAULT_FALLBACK_FEE};
     CFeeRate m_discard_rate{DEFAULT_DISCARD_FEE};
     OutputType m_default_address_type{DEFAULT_ADDRESS_TYPE};
-    OutputType m_default_change_type{DEFAULT_CHANGE_TYPE};
+    /**
+     * Default output type for change outputs. When unset, automatically choose type
+     * based on address type setting and the types other of non-change outputs
+     * (see -changetype option documentation and implementation in
+     * CWallet::TransactionChangeType for details).
+     */
+    Optional<OutputType> m_default_change_type{};
     /** Absolute maximum transaction fee (in satoshis) used by default for the wallet */
     CAmount m_default_max_tx_fee{DEFAULT_TRANSACTION_MAXFEE};