Merge bitcoin/bitcoin#25634: wallet, tests: Expand and test when the blank wallet flag should be un/set

cdba23db353a1beff831ff4fc83d01ed64e8c2a9 wallet: Document blank flag use in descriptor wallets (Ryan Ofsky)
43310200dce8d450ae5808824af788cefaa5d6db wallet: Ensure that the blank wallet flag is unset after imports (Andrew Chow)
e9379f1ffa7a4eebce397f1150317e840655e021 rpc, wallet: Include information about blank flag (Andrew Chow)

Pull request description:

  The `blank` wallet flag is used to indicate that the wallet intentionally does not have any keys, scripts, or descriptors, and it prevents the automatic generation of those things for such a wallet. Once the wallet contains any of those data, it is unnecessary, and possibly incorrect, to have `blank` set. This PR fixes a few places where this was not properly happening. It also adds a test for this unset behavior.

ACKs for top commit:
  S3RK:
    reACK cdba23db353a1beff831ff4fc83d01ed64e8c2a9
  ryanofsky:
    Code review ACK cdba23db353a1beff831ff4fc83d01ed64e8c2a9. Only change since last review is dropping the commit which makes createwallet RPC set BLANK flag automatically when DISABLE_PRIVATE_KEYS flag is set

Tree-SHA512: 85bc2a9754df0531575d5c8f4ad7e8f38dcd50083dc29b3283dacf56feae842e81f34654c5e1781f2dadb0560ff80e454bbc8ca3b2d1fab1b236499ae9abd7da

3 files changed, 12 insertions, 2 deletions

diff --git a/src/wallet/rpc/wallet.cpp b/src/wallet/rpc/wallet.cpp
index e0f246e2f2..340e4115af 100644
--- a/src/wallet/rpc/wallet.cpp
+++ b/src/wallet/rpc/wallet.cpp
@@ -68,6 +68,7 @@ static RPCHelpMan getwalletinfo()
                         }, /*skip_type_check=*/true},
                         {RPCResult::Type::BOOL, "descriptors", "whether this wallet uses descriptors for scriptPubKey management"},
                         {RPCResult::Type::BOOL, "external_signer", "whether this wallet is configured to use an external signer such as a hardware wallet"},
+                        {RPCResult::Type::BOOL, "blank", "Whether this wallet intentionally does not contain any keys, scripts, or descriptors"},
                         RESULT_LAST_PROCESSED_BLOCK,
                     }},
                 },
@@ -130,6 +131,7 @@ static RPCHelpMan getwalletinfo()
     }
     obj.pushKV("descriptors", pwallet->IsWalletFlagSet(WALLET_FLAG_DESCRIPTORS));
     obj.pushKV("external_signer", pwallet->IsWalletFlagSet(WALLET_FLAG_EXTERNAL_SIGNER));
+    obj.pushKV("blank", pwallet->IsWalletFlagSet(WALLET_FLAG_BLANK_WALLET));
 
     AppendLastProcessedBlock(obj, *pwallet);
     return obj;
diff --git a/src/wallet/scriptpubkeyman.cpp b/src/wallet/scriptpubkeyman.cpp
index 1c8d65c583..796b7f11c5 100644
--- a/src/wallet/scriptpubkeyman.cpp
+++ b/src/wallet/scriptpubkeyman.cpp
@@ -757,12 +757,12 @@ bool LegacyScriptPubKeyMan::AddKeyPubKeyWithDB(WalletBatch& batch, const CKey& s
         RemoveWatchOnly(script);
     }
 
+    m_storage.UnsetBlankWalletFlag(batch);
     if (!m_storage.HasEncryptionKeys()) {
         return batch.WriteKey(pubkey,
                                                  secret.GetPrivKey(),
                                                  mapKeyMetadata[pubkey.GetID()]);
     }
-    m_storage.UnsetBlankWalletFlag(batch);
     return true;
 }
 
diff --git a/src/wallet/walletutil.h b/src/wallet/walletutil.h
index 3f0c1228e3..c5975144c1 100644
--- a/src/wallet/walletutil.h
+++ b/src/wallet/walletutil.h
@@ -53,10 +53,18 @@ enum WalletFlags : uint64_t {
     //! Flag set when a wallet contains no HD seed and no private keys, scripts,
     //! addresses, and other watch only things, and is therefore "blank."
     //!
-    //! The only function this flag serves is to distinguish a blank wallet from
+    //! The main function this flag serves is to distinguish a blank wallet from
     //! a newly created wallet when the wallet database is loaded, to avoid
     //! initialization that should only happen on first run.
     //!
+    //! A secondary function of this flag, which applies to descriptor wallets
+    //! only, is to serve as an ongoing indication that descriptors in the
+    //! wallet should be created manually, and that the wallet should not
+    //! generate automatically generate new descriptors if it is later
+    //! encrypted. To support this behavior, descriptor wallets unlike legacy
+    //! wallets do not automatically unset the BLANK flag when things are
+    //! imported.
+    //!
     //! This flag is also a mandatory flag to prevent previous versions of
     //! bitcoin from opening the wallet, thinking it was newly created, and
     //! then improperly reinitializing it.