Allow -upgradewallet to upgradewallets to HD

Changes the maximum upgradewallet version to the latest wallet version
number, 159900. Non-HD wallets will be upgraded to use HD derivation.
Non HD chain split wallets will be upgraded to HD chain split.

If a non-HD wallet is upgraded to HD, the keypool will be entirely
regenerated.

Since upgradewallet is effectively run during a first run, all of the
first run initial setup stuff is combined with the upgrade to HD

src/wallet/wallet.cpp

@@ -4025,6 +4025,35 @@ CWallet* CWallet::CreateWalletFromFile(const std::string& name, const fs::path&
         walletInstance->SetMaxVersion(nMaxVersion);
     }
 
+    // Upgrade to HD if explicit upgrade
+    if (gArgs.GetBoolArg("-upgradewallet", false)) {
+        LOCK(walletInstance->cs_wallet);
+        bool hd_upgrade = false;
+        if (walletInstance->CanSupportFeature(FEATURE_HD) && !walletInstance->IsHDEnabled()) {
+            LogPrintf("Upgrading wallet to HD\n");
+            walletInstance->SetMinVersion(FEATURE_HD);
+
+            // generate a new master key
+            CPubKey masterPubKey = walletInstance->GenerateNewHDMasterKey();
+            if (!walletInstance->SetHDMasterKey(masterPubKey)) {
+                throw std::runtime_error(std::string(__func__) + ": Storing master key failed");
+            }
+            hd_upgrade = true;
+        }
+        // Upgrade to HD chain split if necessary
+        if (walletInstance->CanSupportFeature(FEATURE_HD_SPLIT)) {
+            LogPrintf("Upgrading wallet to use HD chain split\n");
+            walletInstance->SetMinVersion(FEATURE_HD_SPLIT);
+        }
+        // Regenerate the keypool if upgraded to HD
+        if (hd_upgrade) {
+            if (!walletInstance->NewKeyPool()) {
+                InitError(_("Unable to generate keys") += "\n");
+                return nullptr;
+            }
+        }
+    }
+
     if (fFirstRun)
     {
         // ensure this wallet.dat can only be opened by clients supporting HD with chain split and expects no default key
@@ -4032,7 +4061,7 @@ CWallet* CWallet::CreateWalletFromFile(const std::string& name, const fs::path&
             InitError(strprintf(_("Error creating %s: You can't create non-HD wallets with this version."), walletFile));
             return nullptr;
         }
-        walletInstance->SetMinVersion(FEATURE_NO_DEFAULT_KEY);
+        walletInstance->SetMinVersion(FEATURE_LATEST);
 
         // generate a new master key
         CPubKey masterPubKey = walletInstance->GenerateNewHDMasterKey();

src/wallet/wallet.h

@@ -89,7 +89,7 @@ enum WalletFeature
 
     FEATURE_NO_DEFAULT_KEY = 159900, // Wallet without a default key written
 
-    FEATURE_LATEST = FEATURE_COMPRPUBKEY // HD is optional, use FEATURE_COMPRPUBKEY as latest version
+    FEATURE_LATEST = FEATURE_NO_DEFAULT_KEY
 };
 
 enum class OutputType {