rpc: make sure upgradetohd always has the passphrase for UpgradeToHD

earlier it was possible to make it all the way to `EncryptSecret`
without actually having the passphrase in hand until being told off
by `CCrypter::SetKey`, we should avoid that.

also, let's get rid of checks that `UpgradeToHD` is now taking
responsibility for. no point in checking if the wallet is unlocked
as it has no bearing on your ability to upgrade the wallet.

src/wallet/rpcwallet.cpp

@@ -2779,11 +2779,14 @@ static RPCHelpMan upgradetohd()
 {
     return RPCHelpMan{"upgradetohd",
         "\nUpgrades non-HD wallets to HD.\n"
-        "\nWarning: You will need to make a new backup of your wallet after setting the HD wallet mnemonic.\n",
+        "\nThe wallet passphrase must be supplied as it is used to encrypt the HD chain. Unlocking the wallet beforehand\n"
+        "\nhas no bearing on the encryption process and cannot be used in place of supplying the passphrase.\n"
+        "\nSupplying an incorrect passphrase may result in your wallet getting locked.\n"
+        "\n\nWarning: You will need to make a new backup of your wallet after setting the HD wallet mnemonic.\n",
         {
             {"mnemonic", RPCArg::Type::STR, /* default */ "", "Mnemonic as defined in BIP39 to use for the new HD wallet. Use an empty string \"\" to generate a new random mnemonic."},
             {"mnemonicpassphrase", RPCArg::Type::STR, /* default */ "", "Optional mnemonic passphrase as defined in BIP39"},
-            {"walletpassphrase", RPCArg::Type::STR, /* default */ "", "If your wallet is encrypted you must have your wallet passphrase here. If your wallet is not encrypted specifying wallet passphrase will trigger wallet encryption."},
+            {"walletpassphrase", RPCArg::Type::STR, /* default */ "", "If your wallet is encrypted you must have your wallet passphrase here. If your wallet is not encrypted, specifying wallet passphrase will trigger wallet encryption."},
             {"rescan", RPCArg::Type::BOOL, /* default */ "false if mnemonic is empty", "Whether to rescan the blockchain for missing transactions or not"},
         },
         RPCResult{
@@ -2803,17 +2806,17 @@ static RPCHelpMan upgradetohd()
     bool generate_mnemonic = request.params[0].isNull() || request.params[0].get_str().empty();
     SecureString secureWalletPassphrase;
     secureWalletPassphrase.reserve(100);
-    // TODO: get rid of this .c_str() by implementing SecureString::operator=(std::string)
-    // Alternately, find a way to make request.params[0] mlock()'d to begin with.
-    if (!request.params[2].isNull()) {
-        secureWalletPassphrase = request.params[2].get_str().c_str();
-        if (!pwallet->Unlock(secureWalletPassphrase)) {
-            throw JSONRPCError(RPC_WALLET_PASSPHRASE_INCORRECT, "The wallet passphrase entered was incorrect");
+
+    if (request.params[2].isNull()) {
+        if (pwallet->IsCrypted()) {
+            throw JSONRPCError(RPC_WALLET_ERROR, "Wallet encrypted but passphrase not supplied. Please refer to \"help upgradetohd\" for guidance.");
         }
+    } else {
+        // TODO: get rid of this .c_str() by implementing SecureString::operator=(std::string)
+        // Alternately, find a way to make request.params[0] mlock()'d to begin with.
+        secureWalletPassphrase = request.params[2].get_str().c_str();
     }
 
-    EnsureWalletIsUnlocked(pwallet.get());
-
     SecureString secureMnemonic;
     secureMnemonic.reserve(256);
     if (!generate_mnemonic) {
@@ -2825,6 +2828,7 @@ static RPCHelpMan upgradetohd()
     if (!request.params[1].isNull()) {
         secureMnemonicPassphrase = request.params[1].get_str().c_str();
     }
+
     // TODO: breaking changes kept for v21!
     // instead upgradetohd let's use more straightforward 'sethdseed'
     constexpr bool is_v21 = false;

test/functional/wallet_upgradetohd.py

@@ -190,8 +190,8 @@ def run_test(self):
         node.stop()
         node.wait_until_stopped()
         self.start_node(0, extra_args=['-rescan'])
-        assert_raises_rpc_error(-13, "Error: Please enter the wallet passphrase with walletpassphrase first.", node.upgradetohd, mnemonic)
-        assert_raises_rpc_error(-14, "The wallet passphrase entered was incorrect", node.upgradetohd, mnemonic, "", "wrongpass")
+        assert_raises_rpc_error(-4, "Wallet encrypted but passphrase not supplied. Please refer to \"help upgradetohd\" for guidance.", node.upgradetohd, mnemonic)
+        assert_raises_rpc_error(-1, "GenerateNewHDChain: supplied incorrect passphrase", node.upgradetohd, mnemonic, "", "wrongpass")
         assert node.upgradetohd(mnemonic, "", walletpass)
         assert_raises_rpc_error(-13, "Error: Please enter the wallet passphrase with walletpassphrase first.", node.dumphdinfo)
         node.walletpassphrase(walletpass, 100)