wallet: Give deprecation warning when loading a legacy wallet

Author: achow101

src/wallet/wallet.cpp

@@ -245,6 +245,11 @@ std::shared_ptr<CWallet> LoadWalletInternal(WalletContext& context, const std::s
             return nullptr;
         }
 
+        // Legacy wallets are being deprecated, warn if the loaded wallet is legacy
+        if (!wallet->IsWalletFlagSet(WALLET_FLAG_DESCRIPTORS)) {
+            warnings.push_back(_("Wallet loaded successfully. The legacy wallet type is being deprecated and support for creating and opening legacy wallets will be removed in the future. Legacy wallets can be migrated to a descriptor wallet with migratewallet."));
+        }
+
         NotifyWalletLoaded(context, wallet);
         AddWallet(context, wallet);
         wallet->postInitProcess();

test/functional/wallet_backwards_compatibility.py

@@ -264,10 +264,11 @@ def run_test(self):
                 os.path.join(node_master_wallets_dir, "u1_v16")
             )
             load_res = node_master.loadwallet("u1_v16")
-            # Make sure this wallet opens without warnings. See https://github.com/bitcoin/bitcoin/pull/19054
+            # Make sure this wallet opens with only the migration warning. See https://github.com/bitcoin/bitcoin/pull/19054
             if int(node_master.getnetworkinfo()["version"]) >= 249900:
                 # loadwallet#warnings (added in v25) -- only present if there is a warning
-                assert "warnings" not in load_res
+                # Legacy wallets will have only a deprecation warning
+                assert_equal(load_res["warnings"], ["Wallet loaded successfully. The legacy wallet type is being deprecated and support for creating and opening legacy wallets will be removed in the future. Legacy wallets can be migrated to a descriptor wallet with migratewallet."])
             else:
                 # loadwallet#warning (deprecated in v25) -- always present, but empty string if no warning
                 assert_equal(load_res["warning"], '')