rpc: deprecate "warning" field in {create,load,unload,restore}wallet

This string field has been replaced in these four RPCs by a "warnings" field
returning a JSON array of strings.

Author: jonatack

src/wallet/rpc/backup.cpp

@@ -1903,7 +1903,7 @@ RPCHelpMan restorewallet()
             RPCResult::Type::OBJ, "", "",
             {
                 {RPCResult::Type::STR, "name", "The wallet name if restored successfully."},
-                {RPCResult::Type::STR, "warning", "Warning messages, if any, related to restoring the wallet. Multiple messages will be delimited by newlines."},
+                {RPCResult::Type::STR, "warning", /*optional=*/true, "Warning messages, if any, related to restoring the wallet. Multiple messages will be delimited by newlines. (DEPRECATED, returned only if config option -deprecatedrpc=walletwarningfield is passed.)"},
                 {RPCResult::Type::ARR, "warnings", /*optional=*/true, "Warning messages, if any, related to restoring the wallet.",
                 {
                     {RPCResult::Type::STR, "", ""},
@@ -1937,7 +1937,9 @@ RPCHelpMan restorewallet()
 
     UniValue obj(UniValue::VOBJ);
     obj.pushKV("name", wallet->GetName());
-    obj.pushKV("warning", Join(warnings, Untranslated("\n")).original);
+    if (wallet->chain().rpcEnableDeprecated("walletwarningfield")) {
+        obj.pushKV("warning", Join(warnings, Untranslated("\n")).original);
+    }
     PushWarnings(warnings, obj);
 
     return obj;

src/wallet/rpc/wallet.cpp

@@ -207,7 +207,7 @@ static RPCHelpMan loadwallet()
                     RPCResult::Type::OBJ, "", "",
                     {
                         {RPCResult::Type::STR, "name", "The wallet name if loaded successfully."},
-                        {RPCResult::Type::STR, "warning", "Warning messages, if any, related to loading the wallet. Multiple messages will be delimited by newlines."},
+                        {RPCResult::Type::STR, "warning", /*optional=*/true, "Warning messages, if any, related to loading the wallet. Multiple messages will be delimited by newlines. (DEPRECATED, returned only if config option -deprecatedrpc=walletwarningfield is passed.)"},
                         {RPCResult::Type::ARR, "warnings", /*optional=*/true, "Warning messages, if any, related to loading the wallet.",
                         {
                             {RPCResult::Type::STR, "", ""},
@@ -244,7 +244,9 @@ static RPCHelpMan loadwallet()
 
     UniValue obj(UniValue::VOBJ);
     obj.pushKV("name", wallet->GetName());
-    obj.pushKV("warning", Join(warnings, Untranslated("\n")).original);
+    if (wallet->chain().rpcEnableDeprecated("walletwarningfield")) {
+        obj.pushKV("warning", Join(warnings, Untranslated("\n")).original);
+    }
     PushWarnings(warnings, obj);
 
     return obj;
@@ -340,7 +342,7 @@ static RPCHelpMan createwallet()
             RPCResult::Type::OBJ, "", "",
             {
                 {RPCResult::Type::STR, "name", "The wallet name if created successfully. If the wallet was created using a full path, the wallet_name will be the full path."},
-                {RPCResult::Type::STR, "warning", "Warning messages, if any, related to creating the wallet. Multiple messages will be delimited by newlines."},
+                {RPCResult::Type::STR, "warning", /*optional=*/true, "Warning messages, if any, related to creating the wallet. Multiple messages will be delimited by newlines. (DEPRECATED, returned only if config option -deprecatedrpc=walletwarningfield is passed.)"},
                 {RPCResult::Type::ARR, "warnings", /*optional=*/true, "Warning messages, if any, related to creating the wallet.",
                 {
                     {RPCResult::Type::STR, "", ""},
@@ -414,7 +416,9 @@ static RPCHelpMan createwallet()
 
     UniValue obj(UniValue::VOBJ);
     obj.pushKV("name", wallet->GetName());
-    obj.pushKV("warning", Join(warnings, Untranslated("\n")).original);
+    if (wallet->chain().rpcEnableDeprecated("walletwarningfield")) {
+        obj.pushKV("warning", Join(warnings, Untranslated("\n")).original);
+    }
     PushWarnings(warnings, obj);
 
     return obj;
@@ -432,7 +436,7 @@ static RPCHelpMan unloadwallet()
                     {"load_on_startup", RPCArg::Type::BOOL, RPCArg::Optional::OMITTED, "Save wallet name to persistent settings and load on startup. True to add wallet to startup list, false to remove, null to leave unchanged."},
                 },
                 RPCResult{RPCResult::Type::OBJ, "", "", {
-                    {RPCResult::Type::STR, "warning", "Warning messages, if any, related to unloading the wallet. Multiple messages will be delimited by newlines."},
+                    {RPCResult::Type::STR, "warning", /*optional=*/true, "Warning messages, if any, related to unloading the wallet. Multiple messages will be delimited by newlines. (DEPRECATED, returned only if config option -deprecatedrpc=walletwarningfield is passed.)"},
                     {RPCResult::Type::ARR, "warnings", /*optional=*/true, "Warning messages, if any, related to unloading the wallet.",
                     {
                         {RPCResult::Type::STR, "", ""},
@@ -474,13 +478,13 @@ static RPCHelpMan unloadwallet()
             throw JSONRPCError(RPC_MISC_ERROR, "Requested wallet already unloaded");
         }
     }
-
-    UnloadWallet(std::move(wallet));
-
     UniValue result(UniValue::VOBJ);
-    result.pushKV("warning", Join(warnings, Untranslated("\n")).original);
+    if (wallet->chain().rpcEnableDeprecated("walletwarningfield")) {
+        result.pushKV("warning", Join(warnings, Untranslated("\n")).original);
+    }
     PushWarnings(warnings, result);
 
+    UnloadWallet(std::move(wallet));
     return result;
 },
     };

test/functional/wallet_backwards_compatibility.py

@@ -265,7 +265,12 @@ def run_test(self):
             )
             load_res = node_master.loadwallet("u1_v16")
             # Make sure this wallet opens without warnings. See https://github.com/bitcoin/bitcoin/pull/19054
-            assert_equal(load_res['warning'], '')
+            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
+            else:
+                # loadwallet#warning (deprecated in v25) -- always present, but empty string if no warning
+                assert_equal(load_res["warning"], '')
             wallet = node_master.get_wallet_rpc("u1_v16")
             info = wallet.getaddressinfo(v16_addr)
             descriptor = f"wpkh([{info['hdmasterfingerprint']}{hdkeypath[1:]}]{v16_pubkey})"

test/functional/wallet_createwallet.py

@@ -25,6 +25,7 @@ def add_options(self, parser):
 
     def set_test_params(self):
         self.num_nodes = 1
+        self.extra_args = [["-deprecatedrpc=walletwarningfield"]]
 
     def skip_test_if_missing_module(self):
         self.skip_if_no_wallet()