descriptors: Change Parse to return vector of descriptors

When given a descriptor which contins a multipath derivation specifier,
a vector of descriptors will be returned.

src/bench/descriptors.cpp

@@ -18,12 +18,12 @@ static void ExpandDescriptor(benchmark::Bench& bench)
     const std::pair<int64_t, int64_t> range = {0, 1000};
     FlatSigningProvider provider;
     std::string error;
-    auto desc = Parse(desc_str, provider, error);
+    auto descs = Parse(desc_str, provider, error);
 
     bench.run([&] {
         for (int i = range.first; i <= range.second; ++i) {
             std::vector<CScript> scripts;
-            bool success = desc->Expand(i, provider, scripts, provider);
+            bool success = descs[0]->Expand(i, provider, scripts, provider);
             assert(success);
         }
     });

src/bench/wallet_ismine.cpp

@@ -43,8 +43,8 @@ static void WalletIsMine(benchmark::Bench& bench, bool legacy_wallet, int num_co
             key.MakeNewKey(/*fCompressed=*/true);
             FlatSigningProvider keys;
             std::string error;
-            std::unique_ptr<Descriptor> desc = Parse("combo(" + EncodeSecret(key) + ")", keys, error, /*require_checksum=*/false);
-            WalletDescriptor w_desc(std::move(desc), /*creation_time=*/0, /*range_start=*/0, /*range_end=*/0, /*next_index=*/0);
+            std::vector<std::unique_ptr<Descriptor>> desc = Parse("combo(" + EncodeSecret(key) + ")", keys, error, /*require_checksum=*/false);
+            WalletDescriptor w_desc(std::move(desc.at(0)), /*creation_time=*/0, /*range_start=*/0, /*range_end=*/0, /*next_index=*/0);
             auto spkm = wallet->AddWalletDescriptor(w_desc, keys, /*label=*/"", /*internal=*/false);
             assert(spkm);
         }

src/qt/test/wallettests.cpp

@@ -218,8 +218,10 @@ std::shared_ptr<CWallet> SetupDescriptorsWallet(interfaces::Node& node, TestChai
     // Add the coinbase key
     FlatSigningProvider provider;
     std::string error;
-    std::unique_ptr<Descriptor> desc = Parse("combo(" + EncodeSecret(test.coinbaseKey) + ")", provider, error, /* require_checksum=*/ false);
-    assert(desc);
+    auto descs = Parse("combo(" + EncodeSecret(test.coinbaseKey) + ")", provider, error, /* require_checksum=*/ false);
+    assert(!descs.empty());
+    assert(descs.size() == 1);
+    auto& desc = descs.at(0);
     WalletDescriptor w_desc(std::move(desc), 0, 0, 1, 1);
     if (!wallet->AddWalletDescriptor(w_desc, provider, "", false)) assert(false);
     CTxDestination dest = GetDestinationForKey(test.coinbaseKey.GetPubKey(), wallet->m_default_address_type);

src/rpc/mining.cpp

@@ -180,35 +180,36 @@ static UniValue generateBlocks(ChainstateManager& chainman, Mining& miner, const
 static bool getScriptFromDescriptor(const std::string& descriptor, CScript& script, std::string& error)
 {
     FlatSigningProvider key_provider;
-    const auto desc = Parse(descriptor, key_provider, error, /* require_checksum = */ false);
-    if (desc) {
-        if (desc->IsRange()) {
-            throw JSONRPCError(RPC_INVALID_PARAMETER, "Ranged descriptor not accepted. Maybe pass through deriveaddresses first?");
-        }
-
-        FlatSigningProvider provider;
-        std::vector<CScript> scripts;
-        if (!desc->Expand(0, key_provider, scripts, provider)) {
-            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Cannot derive script without private keys");
-        }
+    const auto descs = Parse(descriptor, key_provider, error, /* require_checksum = */ false);
+    if (descs.empty()) return false;
+    if (descs.size() > 1) {
+        throw JSONRPCError(RPC_INVALID_PARAMETER, "Multipath descriptor not accepted");
+    }
+    const auto& desc = descs.at(0);
+    if (desc->IsRange()) {
+        throw JSONRPCError(RPC_INVALID_PARAMETER, "Ranged descriptor not accepted. Maybe pass through deriveaddresses first?");
+    }
 
-        // Combo descriptors can have 2 or 4 scripts, so we can't just check scripts.size() == 1
-        CHECK_NONFATAL(scripts.size() > 0 && scripts.size() <= 4);
+    FlatSigningProvider provider;
+    std::vector<CScript> scripts;
+    if (!desc->Expand(0, key_provider, scripts, provider)) {
+        throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Cannot derive script without private keys");
+    }
 
-        if (scripts.size() == 1) {
-            script = scripts.at(0);
-        } else if (scripts.size() == 4) {
-            // For uncompressed keys, take the 3rd script, since it is p2wpkh
-            script = scripts.at(2);
-        } else {
-            // Else take the 2nd script, since it is p2pkh
-            script = scripts.at(1);
-        }
+    // Combo descriptors can have 2 or 4 scripts, so we can't just check scripts.size() == 1
+    CHECK_NONFATAL(scripts.size() > 0 && scripts.size() <= 4);
 
-        return true;
+    if (scripts.size() == 1) {
+        script = scripts.at(0);
+    } else if (scripts.size() == 4) {
+        // For uncompressed keys, take the 3rd script, since it is p2wpkh
+        script = scripts.at(2);
     } else {
-        return false;
+        // Else take the 2nd script, since it is p2pkh
+        script = scripts.at(1);
     }
+
+    return true;
 }
 
 static RPCHelpMan generatetodescriptor()

src/rpc/output_script.cpp

@@ -175,7 +175,11 @@ static RPCHelpMan getdescriptorinfo()
         RPCResult{
             RPCResult::Type::OBJ, "", "",
             {
-                {RPCResult::Type::STR, "descriptor", "The descriptor in canonical form, without private keys"},
+                {RPCResult::Type::STR, "descriptor", "The descriptor in canonical form, without private keys. For a multipath descriptor, only the first will be returned."},
+                {RPCResult::Type::ARR, "multipath_expansion", /*optional=*/true, "All descriptors produced by expanding multipath derivation elements. Only if the provided descriptor specifies multipath derivation elements.",
+                {
+                    {RPCResult::Type::STR, "", ""},
+                }},
                 {RPCResult::Type::STR, "checksum", "The checksum for the input descriptor"},
                 {RPCResult::Type::BOOL, "isrange", "Whether the descriptor is ranged"},
                 {RPCResult::Type::BOOL, "issolvable", "Whether the descriptor is solvable"},
@@ -191,16 +195,25 @@ static RPCHelpMan getdescriptorinfo()
         {
             FlatSigningProvider provider;
             std::string error;
-            auto desc = Parse(request.params[0].get_str(), provider, error);
-            if (!desc) {
+            auto descs = Parse(request.params[0].get_str(), provider, error);
+            if (descs.empty()) {
                 throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, error);
             }
 
             UniValue result(UniValue::VOBJ);
-            result.pushKV("descriptor", desc->ToString());
+            result.pushKV("descriptor", descs.at(0)->ToString());
+
+            if (descs.size() > 1) {
+                UniValue multipath_descs(UniValue::VARR);
+                for (const auto& d : descs) {
+                    multipath_descs.push_back(d->ToString());
+                }
+                result.pushKV("multipath_expansion", multipath_descs);
+            }
+
             result.pushKV("checksum", GetDescriptorChecksum(request.params[0].get_str()));
-            result.pushKV("isrange", desc->IsRange());
-            result.pushKV("issolvable", desc->IsSolvable());
+            result.pushKV("isrange", descs.at(0)->IsRange());
+            result.pushKV("issolvable", descs.at(0)->IsSolvable());
             result.pushKV("hasprivatekeys", provider.keys.size() > 0);
             return result;
         },
@@ -221,7 +234,8 @@ static RPCHelpMan deriveaddresses()
          "    tr(<pubkey>,multi_a(<n>,<pubkey>,<pubkey>,...))   P2TR-multisig outputs for the given threshold and pubkeys\n"
          "\nIn the above, <pubkey> either refers to a fixed public key in hexadecimal notation, or to an xpub/xprv optionally followed by one\n"
          "or more path elements separated by \"/\", where \"h\" represents a hardened child key.\n"
-         "For more information on output descriptors, see the documentation in the doc/descriptors.md file.\n"},
+         "For more information on output descriptors, see the documentation in the doc/descriptors.md file.\n"
+         "Note that only descriptors that specify a single derivation path can be derived.\n"},
         {
             {"descriptor", RPCArg::Type::STR, RPCArg::Optional::NO, "The descriptor."},
             {"range", RPCArg::Type::RANGE, RPCArg::Optional::OMITTED, "If a ranged descriptor is used, this specifies the end or the range (in [begin,end] notation) to derive."},
@@ -250,11 +264,14 @@ static RPCHelpMan deriveaddresses()
 
             FlatSigningProvider key_provider;
             std::string error;
-            auto desc = Parse(desc_str, key_provider, error, /* require_checksum = */ true);
-            if (!desc) {
+            auto descs = Parse(desc_str, key_provider, error, /* require_checksum = */ true);
+            if (descs.empty()) {
                 throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, error);
             }
-
+            if (descs.size() > 1) {
+                throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Descriptor with multipath derivation path specifiers are not allowed");
+            }
+            auto& desc = descs.at(0);
             if (!desc->IsRange() && request.params.size() > 1) {
                 throw JSONRPCError(RPC_INVALID_PARAMETER, "Range should not be specified for an un-ranged descriptor");
             }

src/rpc/util.cpp

@@ -1337,24 +1337,26 @@ std::vector<CScript> EvalDescriptorStringOrObject(const UniValue& scanobject, Fl
     }
 
     std::string error;
-    auto desc = Parse(desc_str, provider, error);
-    if (!desc) {
+    auto descs = Parse(desc_str, provider, error);
+    if (descs.empty()) {
         throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, error);
     }
-    if (!desc->IsRange()) {
+    if (!descs.at(0)->IsRange()) {
         range.first = 0;
         range.second = 0;
     }
     std::vector<CScript> ret;
     for (int i = range.first; i <= range.second; ++i) {
-        std::vector<CScript> scripts;
-        if (!desc->Expand(i, provider, scripts, provider)) {
-            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, strprintf("Cannot derive script without private keys: '%s'", desc_str));
-        }
-        if (expand_priv) {
-            desc->ExpandPrivate(/*pos=*/i, provider, /*out=*/provider);
+        for (const auto& desc : descs) {
+            std::vector<CScript> scripts;
+            if (!desc->Expand(i, provider, scripts, provider)) {
+                throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, strprintf("Cannot derive script without private keys: '%s'", desc_str));
+            }
+            if (expand_priv) {
+                desc->ExpandPrivate(/*pos=*/i, provider, /*out=*/provider);
+            }
+            std::move(scripts.begin(), scripts.end(), std::back_inserter(ret));
         }
-        std::move(scripts.begin(), scripts.end(), std::back_inserter(ret));
     }
     return ret;
 }

src/script/descriptor.cpp

@@ -2364,14 +2364,21 @@ bool CheckChecksum(Span<const char>& sp, bool require_checksum, std::string& err
     return true;
 }
 
-std::unique_ptr<Descriptor> Parse(const std::string& descriptor, FlatSigningProvider& out, std::string& error, bool require_checksum)
+std::vector<std::unique_ptr<Descriptor>> Parse(const std::string& descriptor, FlatSigningProvider& out, std::string& error, bool require_checksum)
 {
     Span<const char> sp{descriptor};
-    if (!CheckChecksum(sp, require_checksum, error)) return nullptr;
+    if (!CheckChecksum(sp, require_checksum, error)) return {};
     uint32_t key_exp_index = 0;
     auto ret = ParseScript(key_exp_index, sp, ParseScriptContext::TOP, out, error);
-    if (sp.size() == 0 && !ret.empty()) return std::unique_ptr<Descriptor>(std::move(ret.at(0)));
-    return nullptr;
+    if (sp.size() == 0 && !ret.empty()) {
+        std::vector<std::unique_ptr<Descriptor>> descs;
+        descs.reserve(ret.size());
+        for (auto& r : ret) {
+            descs.emplace_back(std::unique_ptr<Descriptor>(std::move(r)));
+        }
+        return descs;
+    }
+    return {};
 }
 
 std::string GetDescriptorChecksum(const std::string& descriptor)

src/script/descriptor.h

@@ -173,9 +173,9 @@ struct Descriptor {
  * is set, the checksum is mandatory - otherwise it is optional.
  *
  * If a parse error occurs, or the checksum is missing/invalid, or anything
- * else is wrong, `nullptr` is returned.
+ * else is wrong, an empty vector is returned.
  */
-std::unique_ptr<Descriptor> Parse(const std::string& descriptor, FlatSigningProvider& out, std::string& error, bool require_checksum = false);
+std::vector<std::unique_ptr<Descriptor>> Parse(const std::string& descriptor, FlatSigningProvider& out, std::string& error, bool require_checksum = false);
 
 /** Get the checksum for a `descriptor`.
  *

src/test/descriptor_tests.cpp

@@ -25,8 +25,8 @@ void CheckUnparsable(const std::string& prv, const std::string& pub, const std::
     std::string error;
     auto parse_priv = Parse(prv, keys_priv, error);
     auto parse_pub = Parse(pub, keys_pub, error);
-    BOOST_CHECK_MESSAGE(!parse_priv, prv);
-    BOOST_CHECK_MESSAGE(!parse_pub, pub);
+    BOOST_CHECK_MESSAGE(parse_priv.empty(), prv);
+    BOOST_CHECK_MESSAGE(parse_pub.empty(), pub);
     BOOST_CHECK_EQUAL(error, expected_error);
 }
 
@@ -139,19 +139,22 @@ void DoCheck(std::string prv, std::string pub, const std::string& norm_pub, int
     std::set<std::vector<uint32_t>> left_paths = paths;
     std::string error;
 
-    std::unique_ptr<Descriptor> parse_priv;
-    std::unique_ptr<Descriptor> parse_pub;
+    std::vector<std::unique_ptr<Descriptor>> parse_privs;
+    std::vector<std::unique_ptr<Descriptor>> parse_pubs;
     // Check that parsing succeeds.
     if (replace_apostrophe_with_h_in_prv) {
         prv = UseHInsteadOfApostrophe(prv);
     }
-    parse_priv = Parse(prv, keys_priv, error);
-    BOOST_CHECK_MESSAGE(parse_priv, error);
+    parse_privs = Parse(prv, keys_priv, error);
+    BOOST_CHECK_MESSAGE(!parse_privs.empty(), error);
     if (replace_apostrophe_with_h_in_pub) {
         pub = UseHInsteadOfApostrophe(pub);
     }
-    parse_pub = Parse(pub, keys_pub, error);
-    BOOST_CHECK_MESSAGE(parse_pub, error);
+    parse_pubs = Parse(pub, keys_pub, error);
+    BOOST_CHECK_MESSAGE(!parse_pubs.empty(), error);
+
+    auto& parse_priv = parse_privs.at(0);
+    auto& parse_pub = parse_pubs.at(0);
 
     // We must be able to estimate the max satisfaction size for any solvable descriptor top descriptor (but combo).
     const bool is_nontop_or_nonsolvable{!parse_priv->IsSolvable() || !parse_priv->GetOutputType()};

src/test/fuzz/descriptor_parse.cpp

@@ -15,14 +15,24 @@
 MockedDescriptorConverter MOCKED_DESC_CONVERTER;
 
 /** Test a successfully parsed descriptor. */
-static void TestDescriptor(const Descriptor& desc, FlatSigningProvider& sig_provider, std::string& dummy)
+static void TestDescriptor(const Descriptor& desc, FlatSigningProvider& sig_provider, std::string& dummy, std::optional<bool>& is_ranged, std::optional<bool>& is_solvable)
 {
     // Trivial helpers.
     (void)desc.IsRange();
-    const bool is_solvable{desc.IsSolvable()};
     (void)desc.IsSingleType();
     (void)desc.GetOutputType();
 
+    if (is_ranged.has_value()) {
+        assert(desc.IsRange() == *is_ranged);
+    } else {
+        is_ranged = desc.IsRange();
+    }
+    if (is_solvable.has_value()) {
+        assert(desc.IsSolvable() == *is_solvable);
+    } else {
+        is_solvable = desc.IsSolvable();
+    }
+
     // Serialization to string representation.
     (void)desc.ToString();
     (void)desc.ToPrivateString(sig_provider, dummy);
@@ -48,7 +58,7 @@ static void TestDescriptor(const Descriptor& desc, FlatSigningProvider& sig_prov
     const auto max_sat_nonmaxsig{desc.MaxSatisfactionWeight(true)};
     const auto max_elems{desc.MaxSatisfactionElems()};
     // We must be able to estimate the max satisfaction size for any solvable descriptor (but combo).
-    const bool is_nontop_or_nonsolvable{!is_solvable || !desc.GetOutputType()};
+    const bool is_nontop_or_nonsolvable{!*is_solvable || !desc.GetOutputType()};
     const bool is_input_size_info_set{max_sat_maxsig && max_sat_nonmaxsig && max_elems};
     assert(is_input_size_info_set || is_nontop_or_nonsolvable);
 }
@@ -77,7 +87,12 @@ FUZZ_TARGET(mocked_descriptor_parse, .init = initialize_mocked_descriptor_parse)
         FlatSigningProvider signing_provider;
         std::string error;
         const auto desc = Parse(*descriptor, signing_provider, error);
-        if (desc) TestDescriptor(*desc, signing_provider, error);
+        std::optional<bool> is_ranged;
+        std::optional<bool> is_solvable;
+        for (const auto& d : desc) {
+            assert(d);
+            TestDescriptor(*d, signing_provider, error, is_ranged, is_solvable);
+        }
     }
 }
 
@@ -91,6 +106,11 @@ FUZZ_TARGET(descriptor_parse, .init = initialize_descriptor_parse)
     std::string error;
     for (const bool require_checksum : {true, false}) {
         const auto desc = Parse(descriptor, signing_provider, error, require_checksum);
-        if (desc) TestDescriptor(*desc, signing_provider, error);
+        std::optional<bool> is_ranged;
+        std::optional<bool> is_solvable;
+        for (const auto& d : desc) {
+            assert(d);
+            TestDescriptor(*d, signing_provider, error, is_ranged, is_solvable);
+        }
     }
 }

src/wallet/rpc/backup.cpp

@@ -1061,10 +1061,11 @@ static UniValue ProcessImportDescriptor(ImportData& import_data, std::map<CKeyID
     const std::string& descriptor = data["desc"].get_str();
     FlatSigningProvider keys;
     std::string error;
-    auto parsed_desc = Parse(descriptor, keys, error, /* require_checksum = */ true);
-    if (!parsed_desc) {
+    auto parsed_descs = Parse(descriptor, keys, error, /* require_checksum = */ true);
+    if (parsed_descs.empty()) {
         throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, error);
     }
+    const auto& parsed_desc = parsed_descs.at(0);
     if (parsed_desc->GetOutputType() == OutputType::BECH32M) {
         throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Bech32m descriptors cannot be imported into legacy wallets");
     }
@@ -1452,10 +1453,11 @@ static UniValue ProcessDescriptorImport(CWallet& wallet, const UniValue& data, c
         // Parse descriptor string
         FlatSigningProvider keys;
         std::string error;
-        auto parsed_desc = Parse(descriptor, keys, error, /* require_checksum = */ true);
-        if (!parsed_desc) {
+        auto parsed_descs = Parse(descriptor, keys, error, /* require_checksum = */ true);
+        if (parsed_descs.empty()) {
             throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, error);
         }
+        auto& parsed_desc = parsed_descs.at(0);
 
         // Range check
         int64_t range_start = 0, range_end = 1, next_index = 0;

src/wallet/rpc/spend.cpp

@@ -660,11 +660,13 @@ CreatedTransactionResult FundTransaction(CWallet& wallet, const CMutableTransact
                 FlatSigningProvider desc_out;
                 std::string error;
                 std::vector<CScript> scripts_temp;
-                std::unique_ptr<Descriptor> desc = Parse(desc_str, desc_out, error, true);
-                if (!desc) {
+                auto descs = Parse(desc_str, desc_out, error, true);
+                if (descs.empty()) {
                     throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("Unable to parse descriptor '%s': %s", desc_str, error));
                 }
-                desc->Expand(0, desc_out, scripts_temp, desc_out);
+                for (auto& desc : descs) {
+                    desc->Expand(0, desc_out, scripts_temp, desc_out);
+                }
                 coinControl.m_external_provider.Merge(std::move(desc_out));
             }
         }