test: add check for getting SigningProvider for a CPubKey

Verify that the DescriptorSPKM method `GetSigningProvider` should
only return a signing provider for the passed public key if its
corresponding private key of the passed public key is available.

Author: theStack

src/wallet/scriptpubkeyman.h

@@ -611,8 +611,6 @@ class DescriptorScriptPubKeyMan : public ScriptPubKeyMan
     mutable std::map<int32_t, FlatSigningProvider> m_map_signing_providers;
     // Fetch the SigningProvider for the given script and optionally include private keys
     std::unique_ptr<FlatSigningProvider> GetSigningProvider(const CScript& script, bool include_private = false) const;
-    // Fetch the SigningProvider for the given pubkey and always include private keys. This should only be called by signing code.
-    std::unique_ptr<FlatSigningProvider> GetSigningProvider(const CPubKey& pubkey) const;
     // Fetch the SigningProvider for a given index and optionally include private keys. Called by the above functions.
     std::unique_ptr<FlatSigningProvider> GetSigningProvider(int32_t index, bool include_private = false) const EXCLUSIVE_LOCKS_REQUIRED(cs_desc_man);
 
@@ -675,6 +673,9 @@ class DescriptorScriptPubKeyMan : public ScriptPubKeyMan
 
     bool CanProvide(const CScript& script, SignatureData& sigdata) override;
 
+    // Fetch the SigningProvider for the given pubkey and always include private keys. This should only be called by signing code.
+    std::unique_ptr<FlatSigningProvider> GetSigningProvider(const CPubKey& pubkey) const;
+
     bool SignTransaction(CMutableTransaction& tx, const std::map<COutPoint, Coin>& coins, int sighash, std::map<int, bilingual_str>& input_errors) const override;
     SigningResult SignMessage(const std::string& message, const PKHash& pkhash, std::string& str_sig) const override;
     std::optional<common::PSBTError> FillPSBT(PartiallySignedTransaction& psbt, const PrecomputedTransactionData& txdata, int sighash_type = SIGHASH_DEFAULT, bool sign = true, bool bip32derivs = false, int* n_signed = nullptr, bool finalize = true) const override;

src/wallet/test/scriptpubkeyman_tests.cpp

@@ -3,6 +3,7 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include <key.h>
+#include <key_io.h>
 #include <test/util/setup_common.h>
 #include <script/solver.h>
 #include <wallet/scriptpubkeyman.h>
@@ -40,5 +41,27 @@ BOOST_AUTO_TEST_CASE(CanProvide)
     BOOST_CHECK(keyman.CanProvide(p2sh_script, data));
 }
 
+BOOST_AUTO_TEST_CASE(DescriptorScriptPubKeyManTests)
+{
+    std::unique_ptr<interfaces::Chain>& chain = m_node.chain;
+
+    CWallet keystore(chain.get(), "", CreateMockableWalletDatabase());
+    auto key_scriptpath = GenerateRandomKey();
+
+    // Verify that a SigningProvider for a pubkey is only returned if its corresponding private key is available
+    auto key_internal = GenerateRandomKey();
+    std::string desc_str = "tr(" + EncodeSecret(key_internal) + ",pk(" + HexStr(key_scriptpath.GetPubKey()) + "))";
+    auto spk_man1 = dynamic_cast<DescriptorScriptPubKeyMan*>(CreateDescriptor(keystore, desc_str, true));
+    BOOST_CHECK(spk_man1 != nullptr);
+    auto signprov_keypath_spendable = spk_man1->GetSigningProvider(key_internal.GetPubKey());
+    BOOST_CHECK(signprov_keypath_spendable != nullptr);
+
+    desc_str = "tr(" + HexStr(XOnlyPubKey::NUMS_H) + ",pk(" + HexStr(key_scriptpath.GetPubKey()) + "))";
+    auto spk_man2 = dynamic_cast<DescriptorScriptPubKeyMan*>(CreateDescriptor(keystore, desc_str, true));
+    BOOST_CHECK(spk_man2 != nullptr);
+    auto signprov_keypath_nums_h = spk_man2->GetSigningProvider(XOnlyPubKey::NUMS_H.GetEvenCorrespondingCPubKey());
+    BOOST_CHECK(signprov_keypath_nums_h == nullptr);
+}
+
 BOOST_AUTO_TEST_SUITE_END()
 } // namespace wallet