[GUI][Bug] Fix editing of CS address labels

Fixes a bug that prevented the editing of Cold Staking address labels in
the address book due to the passing of an empty purpose, which
`CWallet::ParseIntoAddress()` needs in order to determine if an address
is a cold staking type address.

src/qt/walletmodel.cpp

@@ -397,10 +397,8 @@ bool WalletModel::updateAddressBookLabels(const CTxDestination& dest, const std:
     std::map<CTxDestination, AddressBook::CAddressBookData>::iterator mi = wallet->mapAddressBook.find(dest);
 
     // Check if we have a new address or an updated label
-    if (mi == wallet->mapAddressBook.end()) {
+    if (mi == wallet->mapAddressBook.end() || mi->second.name != strName) {
         return wallet->SetAddressBook(dest, strName, strPurpose);
-    } else if (mi->second.name != strName) {
-        return wallet->SetAddressBook(dest, strName, ""); // "" means don't change purpose
     }
     return false;
 }

src/wallet/wallet.cpp

@@ -2880,21 +2880,31 @@ CBitcoinAddress CWallet::ParseIntoAddress(const CTxDestination& dest, const std:
     return CBitcoinAddress(dest, addrType);
 }
 
+/**
+ * TODO: If we ever add new functionality that modifies the purpose of an address book entry
+ * outside of the below situations, we need to also ensure those situations are considered here
+ */
+bool CWallet::UpdatablePurpose(const std::string& strPurpose1, const std::string& strPurpose2)
+{
+    return (strPurpose1 == AddressBook::AddressBookPurpose::DELEGABLE && strPurpose2 == AddressBook::AddressBookPurpose::DELEGATOR) ||
+           (strPurpose1 == AddressBook::AddressBookPurpose::DELEGATOR && strPurpose2 == AddressBook::AddressBookPurpose::DELEGABLE);
+}
+
 bool CWallet::SetAddressBook(const CTxDestination& address, const std::string& strName, const std::string& strPurpose)
 {
     bool fUpdated = HasAddressBook(address);
+    const bool fUpdatePurpose = !fUpdated || UpdatablePurpose(mapAddressBook.at(address).purpose, strPurpose);
     {
         LOCK(cs_wallet); // mapAddressBook
         mapAddressBook[address].name = strName;
-        if (!strPurpose.empty()) /* update purpose only if requested */
-            mapAddressBook[address].purpose = strPurpose;
+        if (!strPurpose.empty() || fUpdatePurpose) mapAddressBook[address].purpose = strPurpose;
     }
     NotifyAddressBookChanged(this, address, strName, ::IsMine(*this, address) != ISMINE_NO,
         strPurpose, (fUpdated ? CT_UPDATED : CT_NEW));
     if (!fFileBacked)
         return false;
-    std::string addressStr = ParseIntoAddress(address, strPurpose).ToString();
-    if (!strPurpose.empty() && !CWalletDB(strWalletFile).WritePurpose(addressStr, strPurpose))
+    std::string addressStr = ParseIntoAddress(address, (strPurpose.empty() && fUpdated) ? mapAddressBook.at(address).purpose : strPurpose).ToString();
+    if ((!fUpdated || fUpdatePurpose) && !CWalletDB(strWalletFile).WritePurpose(addressStr, strPurpose))
         return false;
     return CWalletDB(strWalletFile).WriteName(addressStr, strName);
 }

src/wallet/wallet.h

@@ -519,6 +519,7 @@ class CWallet : public CCryptoKeyStore, public CValidationInterface
 
     static CBitcoinAddress ParseIntoAddress(const CTxDestination& dest, const std::string& purpose);
 
+    bool UpdatablePurpose(const std::string& strPurpose1, const std::string& strPurpose2);
     bool SetAddressBook(const CTxDestination& address, const std::string& strName, const std::string& purpose);
     bool DelAddressBook(const CTxDestination& address, const CChainParams::Base58Type addrType = CChainParams::PUBKEY_ADDRESS);
     bool HasAddressBook(const CTxDestination& address) const;