Implement GetKeypoolOldestTime and only display it if greater than 0

src/wallet/rpcwallet.cpp

@@ -2439,7 +2439,7 @@ static UniValue getwalletinfo(const JSONRPCRequest& request)
                         {RPCResult::Type::STR_AMOUNT, "unconfirmed_balance", "DEPRECATED. Identical to getbalances().mine.untrusted_pending"},
                         {RPCResult::Type::STR_AMOUNT, "immature_balance", "DEPRECATED. Identical to getbalances().mine.immature"},
                         {RPCResult::Type::NUM, "txcount", "the total number of transactions in the wallet"},
-                        {RPCResult::Type::NUM_TIME, "keypoololdest", "the " + UNIX_EPOCH_TIME + " of the oldest pre-generated key in the key pool"},
+                        {RPCResult::Type::NUM_TIME, "keypoololdest", "the " + UNIX_EPOCH_TIME + " of the oldest pre-generated key in the key pool. Legacy wallets only."},
                         {RPCResult::Type::NUM, "keypoolsize", "how many new keys are pre-generated (only counts external keys)"},
                         {RPCResult::Type::NUM, "keypoolsize_hd_internal", "how many new keys are pre-generated for internal use (used for change outputs, only appears if the wallet is using this feature, otherwise external keys are used)"},
                         {RPCResult::Type::NUM_TIME, "unlocked_until", "the " + UNIX_EPOCH_TIME + " until which the wallet is unlocked for transfers, or 0 if the wallet is locked"},
@@ -2472,13 +2472,16 @@ static UniValue getwalletinfo(const JSONRPCRequest& request)
 
     size_t kpExternalSize = pwallet->KeypoolCountExternalKeys();
     const auto bal = pwallet->GetBalance();
+    int64_t kp_oldest = pwallet->GetOldestKeyPoolTime();
     obj.pushKV("walletname", pwallet->GetName());
     obj.pushKV("walletversion", pwallet->GetVersion());
     obj.pushKV("balance", ValueFromAmount(bal.m_mine_trusted));
     obj.pushKV("unconfirmed_balance", ValueFromAmount(bal.m_mine_untrusted_pending));
     obj.pushKV("immature_balance", ValueFromAmount(bal.m_mine_immature));
     obj.pushKV("txcount",       (int)pwallet->mapWallet.size());
-    obj.pushKV("keypoololdest", pwallet->GetOldestKeyPoolTime());
+    if (kp_oldest > 0) {
+        obj.pushKV("keypoololdest", kp_oldest);
+    }
     obj.pushKV("keypoolsize", (int64_t)kpExternalSize);
 
     LegacyScriptPubKeyMan* spk_man = pwallet->GetLegacyScriptPubKeyMan();

src/wallet/scriptpubkeyman.cpp

@@ -1851,7 +1851,9 @@ bool DescriptorScriptPubKeyMan::HavePrivateKeys() const
 
 int64_t DescriptorScriptPubKeyMan::GetOldestKeyPoolTime() const
 {
-    return GetTime();
+    // This is only used for getwalletinfo output and isn't relevant to descriptor wallets.
+    // The magic number 0 indicates that it shouldn't be displayed so that's what we return.
+    return 0;
 }
 
 size_t DescriptorScriptPubKeyMan::KeypoolCountExternalKeys() const