Merge #20403: wallet: upgradewallet fixes, improvements, test coverage

3eb6f8b2e61c24a22ea9396d86672307845f35eb wallet (not for backport): improve upgradewallet error messages (Jon Atack)
ca8cd893bb56bf5d455154b0498b1f58f77d20ed wallet: fix and improve upgradewallet error responses (Jon Atack)
99d56e357159c7154f69f28cb5587c5ca20d6594 wallet: fix and improve upgradewallet result responses (Jon Atack)
2498b04ce88696a3216fc38b7d393906b733e8b1 Don't upgrade to HD split if it is already supported (Andrew Chow)
c46c18b788cb0862aafbb116fd37936cbed6a431 wallet: refactor GetClosestWalletFeature() (Jon Atack)

Pull request description:

  This follows up on #18836 and #20282 to fix and improve the as-yet unreleased `upgradewallet` feature and also implement review follow-up in https://github.com/bitcoin/bitcoin/pull/18836#discussion_r519328607.

  This PR fixes 4 upgradewallet issues:

  - this bug: https://github.com/bitcoin/bitcoin/pull/20403#discussion_r526063920
  - it returns nothing in the absence of an RPC error, which isn't reassuring for users
  - it returns the same thing both in the case of a successful upgrade and when no upgrade took place
  - the error message object is currently dead code

  This PR fixes the above and provides:

  ...user feedback to not silently return without upgrading
  ```
  {
    "wallet_name": "disable private keys",
    "previous_version": 169900,
    "current_version": 169900,
    "result": "Already at latest version. Wallet version unchanged."
  }
  ```
  ...better feedback after successfully upgrading
  ```
  {
    "wallet_name": "watch-only",
    "previous_version": 159900,
    "current_version": 169900,
    "result": "Wallet upgraded successfully from version 159900 to version 169900."
  }
  ```
  ...helpful error responses
  ```
  {
    "wallet_name": "blank",
    "previous_version": 169900,
    "current_version": 169900,
    "error": "Cannot downgrade wallet from version 169900 to version 159900. Wallet version unchanged."
  }
  {
    "wallet_name": "blank",
    "previous_version": 130000,
    "current_version": 130000,
    "error": "Cannot upgrade a non HD split wallet from version 130000 to version 169899 without upgrading to support pre-split keypool. Please use version 169900 or no version specified."
  }
  ```
  updated help:
  ```
  upgradewallet ( version )

  Upgrade the wallet. Upgrades to the latest version if no version number is specified.
  New keys may be generated and a new wallet backup will need to be made.
  Arguments:
  1. version    (numeric, optional, default=169900) The version number to upgrade to. Default is the latest wallet version.

  Result:
  {                            (json object)
    "wallet_name" : "str",     (string) Name of wallet this operation was performed on
    "previous_version" : n,    (numeric) Version of wallet before this operation
    "current_version" : n,     (numeric) Version of wallet after this operation
    "result" : "str",          (string, optional) Description of result, if no error
    "error" : "str"            (string, optional) Error message (if there is one)
  }
  ```

ACKs for top commit:
  achow101:
    ACK  3eb6f8b
  MarcoFalke:
    review ACK 3eb6f8b2e61c24a22ea9396d86672307845f35eb 🛡

Tree-SHA512: b767314069e26b5933b123acfea6aa40708507f504bdb22884da020a4ca1332af38a7072b061e36281533af9f4e236d94d3c129daf6fe5b55241127537038eed

4 files changed, 34 insertions, 19 deletions

diff --git a/src/wallet/rpcwallet.cpp b/src/wallet/rpcwallet.cpp
index 22d8401a3a..e66377c13c 100644
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -4234,7 +4234,7 @@ static RPCHelpMan sethdseed()
 
     // Do not do anything to non-HD wallets
     if (!pwallet->CanSupportFeature(FEATURE_HD)) {
-        throw JSONRPCError(RPC_WALLET_ERROR, "Cannot set a HD seed on a non-HD wallet. Use the upgradewallet RPC in order to upgrade a non-HD wallet to HD");
+        throw JSONRPCError(RPC_WALLET_ERROR, "Cannot set an HD seed on a non-HD wallet. Use the upgradewallet RPC in order to upgrade a non-HD wallet to HD");
     }
 
     EnsureWalletIsUnlocked(pwallet);
@@ -4465,14 +4465,18 @@ static RPCHelpMan walletcreatefundedpsbt()
 static RPCHelpMan upgradewallet()
 {
     return RPCHelpMan{"upgradewallet",
-        "\nUpgrade the wallet. Upgrades to the latest version if no version number is specified\n"
+        "\nUpgrade the wallet. Upgrades to the latest version if no version number is specified.\n"
         "New keys may be generated and a new wallet backup will need to be made.",
         {
-            {"version", RPCArg::Type::NUM, /* default */ strprintf("%d", FEATURE_LATEST), "The version number to upgrade to. Default is the latest wallet version"}
+            {"version", RPCArg::Type::NUM, /* default */ strprintf("%d", FEATURE_LATEST), "The version number to upgrade to. Default is the latest wallet version."}
         },
         RPCResult{
             RPCResult::Type::OBJ, "", "",
             {
+                {RPCResult::Type::STR, "wallet_name", "Name of wallet this operation was performed on"},
+                {RPCResult::Type::NUM, "previous_version", "Version of wallet before this operation"},
+                {RPCResult::Type::NUM, "current_version", "Version of wallet after this operation"},
+                {RPCResult::Type::STR, "result", /* optional */ true, "Description of result, if no error"},
                 {RPCResult::Type::STR, "error", /* optional */ true, "Error message (if there is one)"}
             },
         },
@@ -4495,11 +4499,27 @@ static RPCHelpMan upgradewallet()
         version = request.params[0].get_int();
     }
     bilingual_str error;
-    if (!pwallet->UpgradeWallet(version, error)) {
-        throw JSONRPCError(RPC_WALLET_ERROR, error.original);
+    const int previous_version{pwallet->GetVersion()};
+    const bool wallet_upgraded{pwallet->UpgradeWallet(version, error)};
+    const int current_version{pwallet->GetVersion()};
+    std::string result;
+
+    if (wallet_upgraded) {
+        if (previous_version == current_version) {
+            result = "Already at latest version. Wallet version unchanged.";
+        } else {
+            result = strprintf("Wallet upgraded successfully from version %i to version %i.", previous_version, current_version);
+        }
     }
+
     UniValue obj(UniValue::VOBJ);
-    if (!error.empty()) {
+    obj.pushKV("wallet_name", pwallet->GetName());
+    obj.pushKV("previous_version", previous_version);
+    obj.pushKV("current_version", current_version);
+    if (!result.empty()) {
+        obj.pushKV("result", result);
+    } else {
+        CHECK_NONFATAL(!error.empty());
         obj.pushKV("error", error.original);
     }
     return obj;
diff --git a/src/wallet/scriptpubkeyman.cpp b/src/wallet/scriptpubkeyman.cpp
index 7ed20e4394..15972fe7bb 100644
--- a/src/wallet/scriptpubkeyman.cpp
+++ b/src/wallet/scriptpubkeyman.cpp
@@ -456,7 +456,7 @@ bool LegacyScriptPubKeyMan::Upgrade(int prev_version, int new_version, bilingual
         hd_upgrade = true;
     }
     // Upgrade to HD chain split if necessary
-    if (IsFeatureSupported(new_version, FEATURE_HD_SPLIT)) {
+    if (!IsFeatureSupported(prev_version, FEATURE_HD_SPLIT) && IsFeatureSupported(new_version, FEATURE_HD_SPLIT)) {
         WalletLogPrintf("Upgrading wallet to use HD chain split\n");
         m_storage.SetMinVersion(FEATURE_PRE_SPLIT_KEYPOOL);
         split_upgrade = FEATURE_HD_SPLIT > prev_version;
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index ff8bfff872..3019d53c6c 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -4111,9 +4111,8 @@ bool CWallet::UpgradeWallet(int version, bilingual_str& error)
     } else {
         WalletLogPrintf("Allowing wallet upgrade up to %i\n", version);
     }
-    if (version < prev_version)
-    {
-        error = _("Cannot downgrade wallet");
+    if (version < prev_version) {
+        error = strprintf(_("Cannot downgrade wallet from version %i to version %i. Wallet version unchanged."), prev_version, version);
         return false;
     }
 
@@ -4121,7 +4120,7 @@ bool CWallet::UpgradeWallet(int version, bilingual_str& error)
 
     // Do not upgrade versions to any version between HD_SPLIT and FEATURE_PRE_SPLIT_KEYPOOL unless already supporting HD_SPLIT
     if (!CanSupportFeature(FEATURE_HD_SPLIT) && version >= FEATURE_HD_SPLIT && version < FEATURE_PRE_SPLIT_KEYPOOL) {
-        error = _("Cannot upgrade a non HD split wallet without upgrading to support pre split keypool. Please use version 169900 or no version specified.");
+        error = strprintf(_("Cannot upgrade a non HD split wallet from version %i to version %i without upgrading to support pre-split keypool. Please use version %i or no version specified."), prev_version, version, FEATURE_PRE_SPLIT_KEYPOOL);
         return false;
     }
 
diff --git a/src/wallet/walletutil.cpp b/src/wallet/walletutil.cpp
index d3f76ec66c..9be610e8bd 100644
--- a/src/wallet/walletutil.cpp
+++ b/src/wallet/walletutil.cpp
@@ -91,13 +91,9 @@ bool IsFeatureSupported(int wallet_version, int feature_version)
 
 WalletFeature GetClosestWalletFeature(int version)
 {
-    if (version >= FEATURE_LATEST) return FEATURE_LATEST;
-    if (version >= FEATURE_PRE_SPLIT_KEYPOOL) return FEATURE_PRE_SPLIT_KEYPOOL;
-    if (version >= FEATURE_NO_DEFAULT_KEY) return FEATURE_NO_DEFAULT_KEY;
-    if (version >= FEATURE_HD_SPLIT) return FEATURE_HD_SPLIT;
-    if (version >= FEATURE_HD) return FEATURE_HD;
-    if (version >= FEATURE_COMPRPUBKEY) return FEATURE_COMPRPUBKEY;
-    if (version >= FEATURE_WALLETCRYPT) return FEATURE_WALLETCRYPT;
-    if (version >= FEATURE_BASE) return FEATURE_BASE;
+    const std::array<WalletFeature, 8> wallet_features{{FEATURE_LATEST, FEATURE_PRE_SPLIT_KEYPOOL, FEATURE_NO_DEFAULT_KEY, FEATURE_HD_SPLIT, FEATURE_HD, FEATURE_COMPRPUBKEY, FEATURE_WALLETCRYPT, FEATURE_BASE}};
+    for (const WalletFeature& wf : wallet_features) {
+        if (version >= wf) return wf;
+    }
     return static_cast<WalletFeature>(0);
 }