Merge #12729: Get rid of ambiguous OutputType::NONE value

1e46d8a Get rid of ambiguous OutputType::NONE value (Russell Yanofsky)

Pull request description:

  Based on suggestion by @sipa https://github.com/bitcoin/bitcoin/pull/12119#issuecomment-357982763

  After #12119, the NONE output type was overloaded to refer to either an output type that couldn't be parsed, or to an automatic change output mode.  This change drops the NONE enum and uses a simple bool to indicate parse failure, and a new CHANGE_AUTO enum to refer the change output type.

  This change is almost a pure refactoring except it makes RPCs reject empty string ("") address types instead of treating them like they were unset. This simplifies the parsing code a little bit and could prevent RPC usage mistakes. It's noted in the release notes.

  Follows up #12408 by @MarcoFalke

  Followups for future PRs:

  - [ ] Add explicit support for specifying "auto" in `ParseOutputType` as suggested by promag and sipa: https://github.com/bitcoin/bitcoin/pull/12729#issuecomment-374799567 and https://github.com/bitcoin/bitcoin/pull/12729#discussion_r175969481
  - [ ] Add wallet `AddressChangeType` method to complement `TransactionChangeType`:  https://github.com/bitcoin/bitcoin/pull/12729#discussion_r175969618.

Tree-SHA512: 8b08b272bcb177a0a9e556dcd965840a7fe601ef83ca97938b879c9b1a33b5b3f96939e1bceef11ba7c644ac21bfd6c1dbc6ca715cd1da4ace50475240e4ee48

4 files changed, 31 insertions, 29 deletions

diff --git a/src/qt/paymentserver.cpp b/src/qt/paymentserver.cpp
index 70cdb3361c..59bb5d5bb6 100644
--- a/src/qt/paymentserver.cpp
+++ b/src/qt/paymentserver.cpp
@@ -648,7 +648,7 @@ void PaymentServer::fetchPaymentACK(WalletModel* walletModel, const SendCoinsRec
         // use for change. Despite an actual payment and not change, this is a close match:
         // it's the output type we use subject to privacy issues, but not restricted by what
         // other software supports.
-        const OutputType change_type = walletModel->wallet().getDefaultChangeType() != OutputType::NONE ? walletModel->wallet().getDefaultChangeType() : walletModel->wallet().getDefaultAddressType();
+        const OutputType change_type = walletModel->wallet().getDefaultChangeType() != OutputType::CHANGE_AUTO ? walletModel->wallet().getDefaultChangeType() : walletModel->wallet().getDefaultAddressType();
         walletModel->wallet().learnRelatedScripts(newKey, change_type);
         CTxDestination dest = GetDestinationForKey(newKey, change_type);
         std::string label = tr("Refund from %1").arg(recipient.authenticatedMerchant).toStdString();
diff --git a/src/wallet/rpcwallet.cpp b/src/wallet/rpcwallet.cpp
index a82f069490..bfd9840dfc 100644
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -164,8 +164,7 @@ UniValue getnewaddress(const JSONRPCRequest& request)
 
     OutputType output_type = pwallet->m_default_address_type;
     if (!request.params[1].isNull()) {
-        output_type = ParseOutputType(request.params[1].get_str(), pwallet->m_default_address_type);
-        if (output_type == OutputType::NONE) {
+        if (!ParseOutputType(request.params[1].get_str(), output_type)) {
             throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, strprintf("Unknown address type '%s'", request.params[1].get_str()));
         }
     }
@@ -282,10 +281,9 @@ UniValue getrawchangeaddress(const JSONRPCRequest& request)
         pwallet->TopUpKeyPool();
     }
 
-    OutputType output_type = pwallet->m_default_change_type != OutputType::NONE ? pwallet->m_default_change_type : pwallet->m_default_address_type;
+    OutputType output_type = pwallet->m_default_change_type != OutputType::CHANGE_AUTO ? pwallet->m_default_change_type : pwallet->m_default_address_type;
     if (!request.params[0].isNull()) {
-        output_type = ParseOutputType(request.params[0].get_str(), output_type);
-        if (output_type == OutputType::NONE) {
+        if (!ParseOutputType(request.params[0].get_str(), output_type)) {
             throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, strprintf("Unknown address type '%s'", request.params[0].get_str()));
         }
     }
@@ -1317,8 +1315,7 @@ UniValue addmultisigaddress(const JSONRPCRequest& request)
 
     OutputType output_type = pwallet->m_default_address_type;
     if (!request.params[3].isNull()) {
-        output_type = ParseOutputType(request.params[3].get_str(), output_type);
-        if (output_type == OutputType::NONE) {
+        if (!ParseOutputType(request.params[3].get_str(), output_type)) {
             throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, strprintf("Unknown address type '%s'", request.params[3].get_str()));
         }
     }
@@ -3317,8 +3314,8 @@ UniValue fundrawtransaction(const JSONRPCRequest& request)
             if (options.exists("changeAddress")) {
                 throw JSONRPCError(RPC_INVALID_PARAMETER, "Cannot specify both changeAddress and address_type options");
             }
-            coinControl.m_change_type = ParseOutputType(options["change_type"].get_str(), pwallet->m_default_change_type);
-            if (coinControl.m_change_type == OutputType::NONE) {
+            coinControl.m_change_type = pwallet->m_default_change_type;
+            if (!ParseOutputType(options["change_type"].get_str(), *coinControl.m_change_type)) {
                 throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, strprintf("Unknown change type '%s'", options["change_type"].get_str()));
             }
         }
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index eeab05fd0f..9533e6ff56 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -2674,7 +2674,7 @@ bool CWallet::FundTransaction(CMutableTransaction& tx, CAmount& nFeeRet, int& nC
 OutputType CWallet::TransactionChangeType(OutputType change_type, const std::vector<CRecipient>& vecSend)
 {
     // If -changetype is specified, always use that change type.
-    if (change_type != OutputType::NONE) {
+    if (change_type != OutputType::CHANGE_AUTO) {
         return change_type;
     }
 
@@ -4054,16 +4054,12 @@ CWallet* CWallet::CreateWalletFromFile(const std::string& name, const fs::path&
         }
     }
 
-    walletInstance->m_default_address_type = ParseOutputType(gArgs.GetArg("-addresstype", ""), DEFAULT_ADDRESS_TYPE);
-    if (walletInstance->m_default_address_type == OutputType::NONE) {
+    if (!gArgs.GetArg("-addresstype", "").empty() && !ParseOutputType(gArgs.GetArg("-addresstype", ""), walletInstance->m_default_address_type)) {
         InitError(strprintf("Unknown address type '%s'", gArgs.GetArg("-addresstype", "")));
         return nullptr;
     }
 
-    // If changetype is set in config file or parameter, check that it's valid.
-    // Default to OutputType::NONE if not set.
-    walletInstance->m_default_change_type = ParseOutputType(gArgs.GetArg("-changetype", ""), OutputType::NONE);
-    if (walletInstance->m_default_change_type == OutputType::NONE && !gArgs.GetArg("-changetype", "").empty()) {
+    if (!gArgs.GetArg("-changetype", "").empty() && !ParseOutputType(gArgs.GetArg("-changetype", ""), walletInstance->m_default_change_type)) {
         InitError(strprintf("Unknown change type '%s'", gArgs.GetArg("-changetype", "")));
         return nullptr;
     }
@@ -4311,19 +4307,19 @@ static const std::string OUTPUT_TYPE_STRING_LEGACY = "legacy";
 static const std::string OUTPUT_TYPE_STRING_P2SH_SEGWIT = "p2sh-segwit";
 static const std::string OUTPUT_TYPE_STRING_BECH32 = "bech32";
 
-OutputType ParseOutputType(const std::string& type, OutputType default_type)
+bool ParseOutputType(const std::string& type, OutputType& output_type)
 {
-    if (type.empty()) {
-        return default_type;
-    } else if (type == OUTPUT_TYPE_STRING_LEGACY) {
-        return OutputType::LEGACY;
+    if (type == OUTPUT_TYPE_STRING_LEGACY) {
+        output_type = OutputType::LEGACY;
+        return true;
     } else if (type == OUTPUT_TYPE_STRING_P2SH_SEGWIT) {
-        return OutputType::P2SH_SEGWIT;
+        output_type = OutputType::P2SH_SEGWIT;
+        return true;
     } else if (type == OUTPUT_TYPE_STRING_BECH32) {
-        return OutputType::BECH32;
-    } else {
-        return OutputType::NONE;
+        output_type = OutputType::BECH32;
+        return true;
     }
+    return false;
 }
 
 const std::string& FormatOutputType(OutputType type)
diff --git a/src/wallet/wallet.h b/src/wallet/wallet.h
index d24ae1186f..3208a20f0f 100644
--- a/src/wallet/wallet.h
+++ b/src/wallet/wallet.h
@@ -93,15 +93,24 @@ enum WalletFeature
 };
 
 enum class OutputType {
-    NONE,
     LEGACY,
     P2SH_SEGWIT,
     BECH32,
+
+    /**
+     * Special output type for change outputs only. 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).
+     */
+    CHANGE_AUTO,
 };
 
 //! Default for -addresstype
 constexpr OutputType DEFAULT_ADDRESS_TYPE{OutputType::P2SH_SEGWIT};
 
+//! Default for -changetype
+constexpr OutputType DEFAULT_CHANGE_TYPE{OutputType::CHANGE_AUTO};
 
 /** A key pool entry */
 class CKeyPool
@@ -973,7 +982,7 @@ 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{OutputType::NONE}; // Default to OutputType::NONE if not set by -changetype
+    OutputType m_default_change_type{DEFAULT_CHANGE_TYPE};
 
     bool NewKeyPool();
     size_t KeypoolCountExternalKeys();
@@ -1218,7 +1227,7 @@ public:
     }
 };
 
-OutputType ParseOutputType(const std::string& str, OutputType default_type);
+bool ParseOutputType(const std::string& str, OutputType& output_type);
 const std::string& FormatOutputType(OutputType type);
 
 /**