Merge bitcoin#25594: refactor: Return BResult from restoreWallet

fa475e9 refactor: Return BResult from restoreWallet (MacroFake)
fa8de09 Prepare BResult for non-copyable types (MacroFake)

Pull request description:

  This avoids the `error` in-out param (and if `warnings` is added to `BResult`, it will avoid passing that in-out param as well).

  Also, as it is needed for this change, prepare `BResult` for non-copyable types.

ACKs for top commit:
  w0xlt:
    reACK bitcoin@fa475e9
  ryanofsky:
    Code review ACK fa475e9. Changes since last review were replacing auto with explicit type and splitting commits

Tree-SHA512: 46350883572f13721ddd198f5dfb88d2fa58ebcbda416f74da3563ea15c920fb1e6ff30558526a4ac91c36c21e6afe27751a4e51b7b8bcbcbe805209f4e9014b

Author: MacroFake

src/interfaces/wallet.h

@@ -352,7 +352,7 @@ class WalletLoader : public ChainClient
    virtual std::string getWalletDir() = 0;
 
    //! Restore backup wallet
-   virtual std::unique_ptr<Wallet> restoreWallet(const fs::path& backup_file, const std::string& wallet_name, bilingual_str& error, std::vector<bilingual_str>& warnings) = 0;
+   virtual BResult<std::unique_ptr<Wallet>> restoreWallet(const fs::path& backup_file, const std::string& wallet_name, std::vector<bilingual_str>& warnings) = 0;
 
    //! Return available wallets in wallet directory.
    virtual std::vector<std::string> listWalletDir() = 0;

src/qt/walletcontroller.cpp

@@ -369,9 +369,10 @@ void RestoreWalletActivity::restore(const fs::path& backup_file, const std::stri
         tr("Restoring Wallet <b>%1</b>…").arg(name.toHtmlEscaped()));
 
     QTimer::singleShot(0, worker(), [this, backup_file, wallet_name] {
-        std::unique_ptr<interfaces::Wallet> wallet = node().walletLoader().restoreWallet(backup_file, wallet_name, m_error_message, m_warning_message);
+        auto wallet{node().walletLoader().restoreWallet(backup_file, wallet_name, m_warning_message)};
 
-        if (wallet) m_wallet_model = m_wallet_controller->getOrCreateWallet(std::move(wallet));
+        m_error_message = wallet ? bilingual_str{} : wallet.GetError();
+        if (wallet) m_wallet_model = m_wallet_controller->getOrCreateWallet(wallet.ReleaseObj());
 
         QTimer::singleShot(0, this, &RestoreWalletActivity::finish);
     });

src/wallet/interfaces.cpp

@@ -625,10 +625,13 @@ class WalletLoaderImpl : public WalletLoader
         options.require_existing = true;
         return MakeWallet(m_context, LoadWallet(m_context, name, true /* load_on_start */, options, status, error, warnings));
     }
-    std::unique_ptr<Wallet> restoreWallet(const fs::path& backup_file, const std::string& wallet_name, bilingual_str& error, std::vector<bilingual_str>& warnings) override
+    BResult<std::unique_ptr<Wallet>> restoreWallet(const fs::path& backup_file, const std::string& wallet_name, std::vector<bilingual_str>& warnings) override
     {
         DatabaseStatus status;
-        return MakeWallet(m_context, RestoreWallet(m_context, backup_file, wallet_name, /*load_on_start=*/true, status, error, warnings));
+        bilingual_str error;
+        BResult<std::unique_ptr<Wallet>> wallet{MakeWallet(m_context, RestoreWallet(m_context, backup_file, wallet_name, /*load_on_start=*/true, status, error, warnings))};
+        if (!wallet) return error;
+        return wallet;
     }
     std::string getWalletDir() override
     {