Merge bitcoin/bitcoin#28597: wallet: No BDB creation, unless -deprecatedrpc=create_bdb

fa071aeb61 wallet: No BDB creation, unless -deprecatedrpc=create_bdb (MarcoFalke)

Pull request description:

  With BDB being removed soon, it seems confusing and harmful to allow users to create fresh BDB wallets going forward, as it would load them with an additional burden of having to migrate them soon after.

  Also, it would be good to allow for one release for test (and external) scripts to adapt.

  Fix all issues by introducing the `-deprecatedrpc=create_bdb` setting.

ACKs for top commit:
  Sjors:
    tACK fa071aeb61
  achow101:
    ACK fa071aeb61
  furszy:
    utACK fa071aeb

Tree-SHA512: 37a4c3e4ba659e0ebe2382e71d9c80e42a895d9ad743f5dda7c110fbbb7d2a36f46769982552a9ac0c3a57203379ef164be97aa8033eb7674d6b4da030ba8f9b

src/wallet/rpc/wallet.cpp

@@ -343,7 +343,7 @@ static RPCHelpMan createwallet()
             {"passphrase", RPCArg::Type::STR, RPCArg::Optional::OMITTED, "Encrypt the wallet with this passphrase."},
             {"avoid_reuse", RPCArg::Type::BOOL, RPCArg::Default{false}, "Keep track of coin reuse, and treat dirty and clean coins differently with privacy considerations in mind."},
             {"descriptors", RPCArg::Type::BOOL, RPCArg::Default{true}, "Create a native descriptor wallet. The wallet will use descriptors internally to handle address creation."
-                                                                       " Setting to \"false\" will create a legacy wallet; however, the legacy wallet type is being deprecated and"
+                                                                       " Setting to \"false\" will create a legacy wallet; This is only possible with the -deprecatedrpc=create_bdb setting because, the legacy wallet type is being deprecated and"
                                                                        " support for creating and opening legacy wallets will be removed in the future."},
             {"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."},
             {"external_signer", RPCArg::Type::BOOL, RPCArg::Default{false}, "Use an external signer such as a hardware wallet. Requires -signer to be configured. Wallet creation will fail if keys cannot be fetched. Requires disable_private_keys and descriptors set to true."},
@@ -389,11 +389,16 @@ static RPCHelpMan createwallet()
     if (!request.params[4].isNull() && request.params[4].get_bool()) {
         flags |= WALLET_FLAG_AVOID_REUSE;
     }
-    if (request.params[5].isNull() || request.params[5].get_bool()) {
+    if (self.Arg<bool>(5)) {
 #ifndef USE_SQLITE
         throw JSONRPCError(RPC_WALLET_ERROR, "Compiled without sqlite support (required for descriptor wallets)");
 #endif
         flags |= WALLET_FLAG_DESCRIPTORS;
+    } else {
+        if (!context.chain->rpcEnableDeprecated("create_bdb")) {
+            throw JSONRPCError(RPC_WALLET_ERROR, "BDB wallet creation is deprecated and will be removed in a future release."
+                                                 " In this release it can be re-enabled temporarily with the -deprecatedrpc=create_bdb setting.");
+        }
     }
     if (!request.params[7].isNull() && request.params[7].get_bool()) {
 #ifdef ENABLE_EXTERNAL_SIGNER

test/functional/test_framework/util.py

@@ -404,6 +404,7 @@ def write_config(config_path, *, n, chain, extra_config="", disable_autoconnect=
         f.write("upnp=0\n")
         f.write("natpmp=0\n")
         f.write("shrinkdebugfile=0\n")
+        f.write("deprecatedrpc=create_bdb\n")  # Required to run the tests
         # To improve SQLite wallet performance so that the tests don't timeout, use -unsafesqlitesync
         f.write("unsafesqlitesync=1\n")
         if disable_autoconnect: