Make DescriptorImpl support multiple subscripts

So far, no descriptor exists that supports more than one sub-script
descriptor. This will change with taproot, so prepare for this by
changing the m_subdescriptor_arg from a unique_ptr to a vector of
unique_ptr's.

1 files changed, 47 insertions, 49 deletions

diff --git a/src/script/descriptor.cpp b/src/script/descriptor.cpp
index d15cba1fa8..5fbc740608 100644
--- a/src/script/descriptor.cpp
+++ b/src/script/descriptor.cpp
@@ -481,11 +481,11 @@ class DescriptorImpl : public Descriptor
     const std::string m_name;
 
 protected:
-    //! The sub-descriptor argument (nullptr for everything but SH and WSH).
+    //! The sub-descriptor arguments (empty for everything but SH and WSH).
     //! In doc/descriptors.m this is referred to as SCRIPT expressions sh(SCRIPT)
     //! and wsh(SCRIPT), and distinct from KEY expressions and ADDR expressions.
     //! Subdescriptors can only ever generate a single script.
-    const std::unique_ptr<DescriptorImpl> m_subdescriptor_arg;
+    const std::vector<std::unique_ptr<DescriptorImpl>> m_subdescriptor_args;
 
     //! Return a serialization of anything except pubkey and script arguments, to be prepended to those.
     virtual std::string ToStringExtra() const { return ""; }
@@ -493,22 +493,23 @@ protected:
     /** A helper function to construct the scripts for this descriptor.
      *
      *  This function is invoked once by ExpandHelper.
-
+     *
      *  @param pubkeys The evaluations of the m_pubkey_args field.
-     *  @param script The evaluation of m_subdescriptor_arg (or nullptr when m_subdescriptor_arg is nullptr).
+     *  @param script The evaluations of m_subdescriptor_args (one for each m_subdescriptor_args element).
      *  @param out A FlatSigningProvider to put scripts or public keys in that are necessary to the solver.
      *             The origin info of the provided pubkeys is automatically added.
      *  @return A vector with scriptPubKeys for this descriptor.
      */
-    virtual std::vector<CScript> MakeScripts(const std::vector<CPubKey>& pubkeys, const CScript* script, FlatSigningProvider& out) const = 0;
+    virtual std::vector<CScript> MakeScripts(const std::vector<CPubKey>& pubkeys, Span<const CScript> scripts, FlatSigningProvider& out) const = 0;
 
 public:
-    DescriptorImpl(std::vector<std::unique_ptr<PubkeyProvider>> pubkeys, std::unique_ptr<DescriptorImpl> script, const std::string& name) : m_pubkey_args(std::move(pubkeys)), m_name(name), m_subdescriptor_arg(std::move(script)) {}
+    DescriptorImpl(std::vector<std::unique_ptr<PubkeyProvider>> pubkeys, const std::string& name) : m_pubkey_args(std::move(pubkeys)), m_name(name), m_subdescriptor_args() {}
+    DescriptorImpl(std::vector<std::unique_ptr<PubkeyProvider>> pubkeys, std::unique_ptr<DescriptorImpl> script, const std::string& name) : m_pubkey_args(std::move(pubkeys)), m_name(name), m_subdescriptor_args(Vector(std::move(script))) {}
 
     bool IsSolvable() const override
     {
-        if (m_subdescriptor_arg) {
-            if (!m_subdescriptor_arg->IsSolvable()) return false;
+        for (const auto& arg : m_subdescriptor_args) {
+            if (!arg->IsSolvable()) return false;
         }
         return true;
     }
@@ -518,8 +519,8 @@ public:
         for (const auto& pubkey : m_pubkey_args) {
             if (pubkey->IsRange()) return true;
         }
-        if (m_subdescriptor_arg) {
-            if (m_subdescriptor_arg->IsRange()) return true;
+        for (const auto& arg : m_subdescriptor_args) {
+            if (arg->IsRange()) return true;
         }
         return false;
     }
@@ -541,10 +542,10 @@ public:
             }
             ret += std::move(tmp);
         }
-        if (m_subdescriptor_arg) {
+        for (const auto& scriptarg : m_subdescriptor_args) {
             if (pos++) ret += ",";
             std::string tmp;
-            if (!m_subdescriptor_arg->ToStringHelper(arg, tmp, priv, normalized)) return false;
+            if (!scriptarg->ToStringHelper(arg, tmp, priv, normalized)) return false;
             ret += std::move(tmp);
         }
         out = std::move(ret) + ")";
@@ -577,18 +578,20 @@ public:
         std::vector<std::pair<CPubKey, KeyOriginInfo>> entries;
         entries.reserve(m_pubkey_args.size());
 
-        // Construct temporary data in `entries` and `subscripts`, to avoid producing output in case of failure.
+        // Construct temporary data in `entries`, `subscripts`, and `subprovider` to avoid producing output in case of failure.
         for (const auto& p : m_pubkey_args) {
             entries.emplace_back();
             if (!p->GetPubKey(pos, arg, entries.back().first, entries.back().second, read_cache, write_cache)) return false;
         }
         std::vector<CScript> subscripts;
-        if (m_subdescriptor_arg) {
-            FlatSigningProvider subprovider;
-            if (!m_subdescriptor_arg->ExpandHelper(pos, arg, read_cache, subscripts, subprovider, write_cache)) return false;
-            assert(subscripts.size() == 1);
-            out = Merge(out, subprovider);
+        FlatSigningProvider subprovider;
+        for (const auto& subarg : m_subdescriptor_args) {
+            std::vector<CScript> outscripts;
+            if (!subarg->ExpandHelper(pos, arg, read_cache, outscripts, subprovider, write_cache)) return false;
+            assert(outscripts.size() == 1);
+            subscripts.emplace_back(std::move(outscripts[0]));
         }
+        out = Merge(std::move(out), std::move(subprovider));
 
         std::vector<CPubKey> pubkeys;
         pubkeys.reserve(entries.size());
@@ -596,11 +599,8 @@ public:
             pubkeys.push_back(entry.first);
             out.origins.emplace(entry.first.GetID(), std::make_pair<CPubKey, KeyOriginInfo>(CPubKey(entry.first), std::move(entry.second)));
         }
-        if (m_subdescriptor_arg) {
-            output_scripts = MakeScripts(pubkeys, &subscripts[0], out);
-        } else {
-            output_scripts = MakeScripts(pubkeys, nullptr, out);
-        }
+
+        output_scripts = MakeScripts(pubkeys, MakeSpan(subscripts), out);
         return true;
     }
 
@@ -621,10 +621,8 @@ public:
             if (!p->GetPrivKey(pos, provider, key)) continue;
             out.keys.emplace(key.GetPubKey().GetID(), key);
         }
-        if (m_subdescriptor_arg) {
-            FlatSigningProvider subprovider;
-            m_subdescriptor_arg->ExpandPrivate(pos, provider, subprovider);
-            out = Merge(out, subprovider);
+        for (const auto& arg : m_subdescriptor_args) {
+            arg->ExpandPrivate(pos, provider, out);
         }
     }
 
@@ -637,9 +635,9 @@ class AddressDescriptor final : public DescriptorImpl
     const CTxDestination m_destination;
 protected:
     std::string ToStringExtra() const override { return EncodeDestination(m_destination); }
-    std::vector<CScript> MakeScripts(const std::vector<CPubKey>&, const CScript*, FlatSigningProvider&) const override { return Vector(GetScriptForDestination(m_destination)); }
+    std::vector<CScript> MakeScripts(const std::vector<CPubKey>&, Span<const CScript>, FlatSigningProvider&) const override { return Vector(GetScriptForDestination(m_destination)); }
 public:
-    AddressDescriptor(CTxDestination destination) : DescriptorImpl({}, {}, "addr"), m_destination(std::move(destination)) {}
+    AddressDescriptor(CTxDestination destination) : DescriptorImpl({}, "addr"), m_destination(std::move(destination)) {}
     bool IsSolvable() const final { return false; }
 
     std::optional<OutputType> GetOutputType() const override
@@ -663,9 +661,9 @@ class RawDescriptor final : public DescriptorImpl
     const CScript m_script;
 protected:
     std::string ToStringExtra() const override { return HexStr(m_script); }
-    std::vector<CScript> MakeScripts(const std::vector<CPubKey>&, const CScript*, FlatSigningProvider&) const override { return Vector(m_script); }
+    std::vector<CScript> MakeScripts(const std::vector<CPubKey>&, Span<const CScript>, FlatSigningProvider&) const override { return Vector(m_script); }
 public:
-    RawDescriptor(CScript script) : DescriptorImpl({}, {}, "raw"), m_script(std::move(script)) {}
+    RawDescriptor(CScript script) : DescriptorImpl({}, "raw"), m_script(std::move(script)) {}
     bool IsSolvable() const final { return false; }
 
     std::optional<OutputType> GetOutputType() const override
@@ -689,9 +687,9 @@ public:
 class PKDescriptor final : public DescriptorImpl
 {
 protected:
-    std::vector<CScript> MakeScripts(const std::vector<CPubKey>& keys, const CScript*, FlatSigningProvider&) const override { return Vector(GetScriptForRawPubKey(keys[0])); }
+    std::vector<CScript> MakeScripts(const std::vector<CPubKey>& keys, Span<const CScript>, FlatSigningProvider&) const override { return Vector(GetScriptForRawPubKey(keys[0])); }
 public:
-    PKDescriptor(std::unique_ptr<PubkeyProvider> prov) : DescriptorImpl(Vector(std::move(prov)), {}, "pk") {}
+    PKDescriptor(std::unique_ptr<PubkeyProvider> prov) : DescriptorImpl(Vector(std::move(prov)), "pk") {}
     bool IsSingleType() const final { return true; }
 };
 
@@ -699,14 +697,14 @@ public:
 class PKHDescriptor final : public DescriptorImpl
 {
 protected:
-    std::vector<CScript> MakeScripts(const std::vector<CPubKey>& keys, const CScript*, FlatSigningProvider& out) const override
+    std::vector<CScript> MakeScripts(const std::vector<CPubKey>& keys, Span<const CScript>, FlatSigningProvider& out) const override
     {
         CKeyID id = keys[0].GetID();
         out.pubkeys.emplace(id, keys[0]);
         return Vector(GetScriptForDestination(PKHash(id)));
     }
 public:
-    PKHDescriptor(std::unique_ptr<PubkeyProvider> prov) : DescriptorImpl(Vector(std::move(prov)), {}, "pkh") {}
+    PKHDescriptor(std::unique_ptr<PubkeyProvider> prov) : DescriptorImpl(Vector(std::move(prov)), "pkh") {}
     std::optional<OutputType> GetOutputType() const override { return OutputType::LEGACY; }
     bool IsSingleType() const final { return true; }
 };
@@ -715,14 +713,14 @@ public:
 class WPKHDescriptor final : public DescriptorImpl
 {
 protected:
-    std::vector<CScript> MakeScripts(const std::vector<CPubKey>& keys, const CScript*, FlatSigningProvider& out) const override
+    std::vector<CScript> MakeScripts(const std::vector<CPubKey>& keys, Span<const CScript>, FlatSigningProvider& out) const override
     {
         CKeyID id = keys[0].GetID();
         out.pubkeys.emplace(id, keys[0]);
         return Vector(GetScriptForDestination(WitnessV0KeyHash(id)));
     }
 public:
-    WPKHDescriptor(std::unique_ptr<PubkeyProvider> prov) : DescriptorImpl(Vector(std::move(prov)), {}, "wpkh") {}
+    WPKHDescriptor(std::unique_ptr<PubkeyProvider> prov) : DescriptorImpl(Vector(std::move(prov)), "wpkh") {}
     std::optional<OutputType> GetOutputType() const override { return OutputType::BECH32; }
     bool IsSingleType() const final { return true; }
 };
@@ -731,7 +729,7 @@ public:
 class ComboDescriptor final : public DescriptorImpl
 {
 protected:
-    std::vector<CScript> MakeScripts(const std::vector<CPubKey>& keys, const CScript*, FlatSigningProvider& out) const override
+    std::vector<CScript> MakeScripts(const std::vector<CPubKey>& keys, Span<const CScript>, FlatSigningProvider& out) const override
     {
         std::vector<CScript> ret;
         CKeyID id = keys[0].GetID();
@@ -747,7 +745,7 @@ protected:
         return ret;
     }
 public:
-    ComboDescriptor(std::unique_ptr<PubkeyProvider> prov) : DescriptorImpl(Vector(std::move(prov)), {}, "combo") {}
+    ComboDescriptor(std::unique_ptr<PubkeyProvider> prov) : DescriptorImpl(Vector(std::move(prov)), "combo") {}
     bool IsSingleType() const final { return false; }
 };
 
@@ -758,7 +756,7 @@ class MultisigDescriptor final : public DescriptorImpl
     const bool m_sorted;
 protected:
     std::string ToStringExtra() const override { return strprintf("%i", m_threshold); }
-    std::vector<CScript> MakeScripts(const std::vector<CPubKey>& keys, const CScript*, FlatSigningProvider&) const override {
+    std::vector<CScript> MakeScripts(const std::vector<CPubKey>& keys, Span<const CScript>, FlatSigningProvider&) const override {
         if (m_sorted) {
             std::vector<CPubKey> sorted_keys(keys);
             std::sort(sorted_keys.begin(), sorted_keys.end());
@@ -767,7 +765,7 @@ protected:
         return Vector(GetScriptForMultisig(m_threshold, keys));
     }
 public:
-    MultisigDescriptor(int threshold, std::vector<std::unique_ptr<PubkeyProvider>> providers, bool sorted = false) : DescriptorImpl(std::move(providers), {}, sorted ? "sortedmulti" : "multi"), m_threshold(threshold), m_sorted(sorted) {}
+    MultisigDescriptor(int threshold, std::vector<std::unique_ptr<PubkeyProvider>> providers, bool sorted = false) : DescriptorImpl(std::move(providers), sorted ? "sortedmulti" : "multi"), m_threshold(threshold), m_sorted(sorted) {}
     bool IsSingleType() const final { return true; }
 };
 
@@ -775,10 +773,10 @@ public:
 class SHDescriptor final : public DescriptorImpl
 {
 protected:
-    std::vector<CScript> MakeScripts(const std::vector<CPubKey>&, const CScript* script, FlatSigningProvider& out) const override
+    std::vector<CScript> MakeScripts(const std::vector<CPubKey>&, Span<const CScript> scripts, FlatSigningProvider& out) const override
     {
-        auto ret = Vector(GetScriptForDestination(ScriptHash(*script)));
-        if (ret.size()) out.scripts.emplace(CScriptID(*script), *script);
+        auto ret = Vector(GetScriptForDestination(ScriptHash(scripts[0])));
+        if (ret.size()) out.scripts.emplace(CScriptID(scripts[0]), scripts[0]);
         return ret;
     }
 public:
@@ -786,8 +784,8 @@ public:
 
     std::optional<OutputType> GetOutputType() const override
     {
-        assert(m_subdescriptor_arg);
-        if (m_subdescriptor_arg->GetOutputType() == OutputType::BECH32) return OutputType::P2SH_SEGWIT;
+        assert(m_subdescriptor_args.size() == 1);
+        if (m_subdescriptor_args[0]->GetOutputType() == OutputType::BECH32) return OutputType::P2SH_SEGWIT;
         return OutputType::LEGACY;
     }
     bool IsSingleType() const final { return true; }
@@ -797,10 +795,10 @@ public:
 class WSHDescriptor final : public DescriptorImpl
 {
 protected:
-    std::vector<CScript> MakeScripts(const std::vector<CPubKey>&, const CScript* script, FlatSigningProvider& out) const override
+    std::vector<CScript> MakeScripts(const std::vector<CPubKey>&, Span<const CScript> scripts, FlatSigningProvider& out) const override
     {
-        auto ret = Vector(GetScriptForDestination(WitnessV0ScriptHash(*script)));
-        if (ret.size()) out.scripts.emplace(CScriptID(*script), *script);
+        auto ret = Vector(GetScriptForDestination(WitnessV0ScriptHash(scripts[0])));
+        if (ret.size()) out.scripts.emplace(CScriptID(scripts[0]), scripts[0]);
         return ret;
     }
 public: