script/signingprovider: introduce a MultiSigningProvider

It is sometimes useful to interface with multiple signing providers at
once. For instance when inferring a descriptor with solving information
being provided from multiple sources (see next commit).

Instead of inneficiently copying the information from one provider into
the other, introduce a new signing provider that takes a list of
pointers to existing providers.

Author: darosior

src/script/signingprovider.cpp

@@ -225,6 +225,61 @@ CKeyID GetKeyForDestination(const SigningProvider& store, const CTxDestination&
     }
     return CKeyID();
 }
+
+void MultiSigningProvider::AddProvider(std::unique_ptr<SigningProvider> provider)
+{
+    m_providers.push_back(std::move(provider));
+}
+
+bool MultiSigningProvider::GetCScript(const CScriptID& scriptid, CScript& script) const
+{
+    for (const auto& provider: m_providers) {
+        if (provider->GetCScript(scriptid, script)) return true;
+    }
+    return false;
+}
+
+bool MultiSigningProvider::GetPubKey(const CKeyID& keyid, CPubKey& pubkey) const
+{
+    for (const auto& provider: m_providers) {
+        if (provider->GetPubKey(keyid, pubkey)) return true;
+    }
+    return false;
+}
+
+
+bool MultiSigningProvider::GetKeyOrigin(const CKeyID& keyid, KeyOriginInfo& info) const
+{
+    for (const auto& provider: m_providers) {
+        if (provider->GetKeyOrigin(keyid, info)) return true;
+    }
+    return false;
+}
+
+bool MultiSigningProvider::GetKey(const CKeyID& keyid, CKey& key) const
+{
+    for (const auto& provider: m_providers) {
+        if (provider->GetKey(keyid, key)) return true;
+    }
+    return false;
+}
+
+bool MultiSigningProvider::GetTaprootSpendData(const XOnlyPubKey& output_key, TaprootSpendData& spenddata) const
+{
+    for (const auto& provider: m_providers) {
+        if (provider->GetTaprootSpendData(output_key, spenddata)) return true;
+    }
+    return false;
+}
+
+bool MultiSigningProvider::GetTaprootBuilder(const XOnlyPubKey& output_key, TaprootBuilder& builder) const
+{
+    for (const auto& provider: m_providers) {
+        if (provider->GetTaprootBuilder(output_key, builder)) return true;
+    }
+    return false;
+}
+
 /*static*/ TaprootBuilder::NodeInfo TaprootBuilder::Combine(NodeInfo&& a, NodeInfo&& b)
 {
     NodeInfo ret;

src/script/signingprovider.h

@@ -298,4 +298,19 @@ class FillableSigningProvider : public SigningProvider
 /** Return the CKeyID of the key involved in a script (if there is a unique one). */
 CKeyID GetKeyForDestination(const SigningProvider& store, const CTxDestination& dest);
 
+/** A signing provider to be used to interface with multiple signing providers at once. */
+class MultiSigningProvider: public SigningProvider {
+    std::vector<std::unique_ptr<SigningProvider>> m_providers;
+
+public:
+    void AddProvider(std::unique_ptr<SigningProvider> provider);
+
+    bool GetCScript(const CScriptID& scriptid, CScript& script) const override;
+    bool GetPubKey(const CKeyID& keyid, CPubKey& pubkey) const override;
+    bool GetKeyOrigin(const CKeyID& keyid, KeyOriginInfo& info) const override;
+    bool GetKey(const CKeyID& keyid, CKey& key) const override;
+    bool GetTaprootSpendData(const XOnlyPubKey& output_key, TaprootSpendData& spenddata) const override;
+    bool GetTaprootBuilder(const XOnlyPubKey& output_key, TaprootBuilder& builder) const override;
+};
+
 #endif // BITCOIN_SCRIPT_SIGNINGPROVIDER_H