wallet: Allow MigrateLegacyToDescriptor to take a wallet name

An overload of MigrateLegacyToDescriptor is added which takes the wallet
name. The original that took a wallet pointer is still available, it
just gets the name, closes the wallet, and calls the new overload.

src/wallet/rpc/wallet.cpp

@@ -737,6 +737,8 @@ static RPCHelpMan migratewallet()
             + HelpExampleRpc("migratewallet", "")
         },
         [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
+        {
+            std::string wallet_name;
             {
                 std::shared_ptr<CWallet> wallet = GetWalletForJSONRPCRequest(request);
                 if (!wallet) return NullUniValue;
@@ -744,10 +746,12 @@ static RPCHelpMan migratewallet()
                 if (wallet->IsCrypted()) {
                     throw JSONRPCError(RPC_WALLET_WRONG_ENC_STATE, "Error: migratewallet on encrypted wallets is currently unsupported.");
                 }
+                wallet_name = wallet->GetName();
+            }
 
             WalletContext& context = EnsureWalletContext(request.context);
 
-            util::Result<MigrationResult> res = MigrateLegacyToDescriptor(std::move(wallet), context);
+            util::Result<MigrationResult> res = MigrateLegacyToDescriptor(wallet_name, context);
             if (!res) {
                 throw JSONRPCError(RPC_WALLET_ERROR, util::ErrorString(res).original);
             }

src/wallet/wallet.cpp

@@ -4165,32 +4165,19 @@ bool DoMigration(CWallet& wallet, WalletContext& context, bilingual_str& error,
     return true;
 }
 
-util::Result<MigrationResult> MigrateLegacyToDescriptor(std::shared_ptr<CWallet>&& wallet, WalletContext& context)
+util::Result<MigrationResult> MigrateLegacyToDescriptor(const std::string& wallet_name, WalletContext& context)
 {
-    // Before anything else, check if there is something to migrate.
-    if (!wallet->GetLegacyScriptPubKeyMan()) {
-        return util::Error{_("Error: This wallet is already a descriptor wallet")};
-    }
-
     MigrationResult res;
     bilingual_str error;
     std::vector<bilingual_str> warnings;
 
-    // Make a backup of the DB
+    // If the wallet is still loaded, unload it so that nothing else tries to use it while we're changing it
-    std::string wallet_name = wallet->GetName();
+    if (auto wallet = GetWallet(context, wallet_name)) {
-    fs::path this_wallet_dir = fs::absolute(fs::PathFromString(wallet->GetDatabase().Filename())).parent_path();
-    fs::path backup_filename = fs::PathFromString(strprintf("%s-%d.legacy.bak", wallet_name, GetTime()));
-    fs::path backup_path = this_wallet_dir / backup_filename;
-    if (!wallet->BackupWallet(fs::PathToString(backup_path))) {
-        return util::Error{_("Error: Unable to make a backup of your wallet")};
-    }
-    res.backup_path = backup_path;
-
-    // Unload the wallet so that nothing else tries to use it while we're changing it
         if (!RemoveWallet(context, wallet, /*load_on_start=*/std::nullopt, warnings)) {
             return util::Error{_("Unable to unload the wallet before migrating")};
         }
         UnloadWallet(std::move(wallet));
+    }
 
     // Load the wallet but only in the context of this function.
     // No signals should be connected nor should anything else be aware of this wallet
@@ -4204,11 +4191,26 @@ util::Result<MigrationResult> MigrateLegacyToDescriptor(std::shared_ptr<CWallet>
         return util::Error{Untranslated("Wallet file verification failed.") + Untranslated(" ") + error};
     }
 
+    // Make the local wallet
     std::shared_ptr<CWallet> local_wallet = CWallet::Create(empty_context, wallet_name, std::move(database), options.create_flags, error, warnings);
     if (!local_wallet) {
         return util::Error{Untranslated("Wallet loading failed.") + Untranslated(" ") + error};
     }
 
+    // Before anything else, check if there is something to migrate.
+    if (!local_wallet->GetLegacyScriptPubKeyMan()) {
+        return util::Error{_("Error: This wallet is already a descriptor wallet")};
+    }
+
+    // Make a backup of the DB
+    fs::path this_wallet_dir = fs::absolute(fs::PathFromString(local_wallet->GetDatabase().Filename())).parent_path();
+    fs::path backup_filename = fs::PathFromString(strprintf("%s-%d.legacy.bak", wallet_name, GetTime()));
+    fs::path backup_path = this_wallet_dir / backup_filename;
+    if (!local_wallet->BackupWallet(fs::PathToString(backup_path))) {
+        return util::Error{_("Error: Unable to make a backup of your wallet")};
+    }
+    res.backup_path = backup_path;
+
     bool success = false;
     {
         LOCK(local_wallet->cs_wallet);

src/wallet/wallet.h

@@ -1007,7 +1007,7 @@ struct MigrationResult {
 };
 
 //! Do all steps to migrate a legacy wallet to a descriptor wallet
-util::Result<MigrationResult> MigrateLegacyToDescriptor(std::shared_ptr<CWallet>&& wallet, WalletContext& context);
+util::Result<MigrationResult> MigrateLegacyToDescriptor(const std::string& wallet_name, WalletContext& context);
 } // namespace wallet
 
 #endif // BITCOIN_WALLET_WALLET_H