Box the wallet: Add multiple keyman maps and loops

Add wallet logic for dealing with multiple ScriptPubKeyMan instances. This
doesn't change current behavior because there is still only a single
LegacyScriptPubKeyMan. But in the future the new logic will be used to support
descriptor wallets.

Author: achow101

src/wallet/scriptpubkeyman.cpp

@@ -470,6 +470,34 @@ int64_t LegacyScriptPubKeyMan::GetTimeFirstKey() const
     return nTimeFirstKey;
 }
 
+const SigningProvider* LegacyScriptPubKeyMan::GetSigningProvider(const CScript& script) const
+{
+    return this;
+}
+
+bool LegacyScriptPubKeyMan::CanProvide(const CScript& script, SignatureData& sigdata)
+{
+    if (IsMine(script) != ISMINE_NO) {
+        // If it IsMine, we can always provide in some way
+        return true;
+    } else if (HaveCScript(CScriptID(script))) {
+        // We can still provide some stuff if we have the script, but IsMine failed because we don't have keys
+        return true;
+    } else {
+        // If, given the stuff in sigdata, we could make a valid sigature, then we can provide for this script
+        ProduceSignature(*this, DUMMY_SIGNATURE_CREATOR, script, sigdata);
+        if (!sigdata.signatures.empty()) {
+            // If we could make signatures, make sure we have a private key to actually make a signature
+            bool has_privkeys = false;
+            for (const auto& key_sig_pair : sigdata.signatures) {
+                has_privkeys |= HaveKey(key_sig_pair.first);
+            }
+            return has_privkeys;
+        }
+        return false;
+    }
+}
+
 const CKeyMetadata* LegacyScriptPubKeyMan::GetMetadata(const CTxDestination& dest) const
 {
     LOCK(cs_KeyStore);
@@ -491,6 +519,11 @@ const CKeyMetadata* LegacyScriptPubKeyMan::GetMetadata(const CTxDestination& des
     return nullptr;
 }
 
+uint256 LegacyScriptPubKeyMan::GetID() const
+{
+    return UINT256_ONE();
+}
+
 /**
  * Update wallet first key creation time. This should be called whenever keys
  * are added to the wallet, with the oldest key creation time.

src/wallet/scriptpubkeyman.h

@@ -196,8 +196,16 @@ class ScriptPubKeyMan
 
     virtual int64_t GetTimeFirstKey() const { return 0; }
 
-    //! Return address metadata
     virtual const CKeyMetadata* GetMetadata(const CTxDestination& dest) const { return nullptr; }
+
+    virtual const SigningProvider* GetSigningProvider(const CScript& script) const { return nullptr; }
+
+    /** Whether this ScriptPubKeyMan can provide a SigningProvider (via GetSigningProvider) that, combined with
+      * sigdata, can produce a valid signature.
+      */
+    virtual bool CanProvide(const CScript& script, SignatureData& sigdata) { return false; }
+
+    virtual uint256 GetID() const { return uint256(); }
 };
 
 class LegacyScriptPubKeyMan : public ScriptPubKeyMan, public FillableSigningProvider
@@ -319,6 +327,12 @@ class LegacyScriptPubKeyMan : public ScriptPubKeyMan, public FillableSigningProv
 
     bool CanGetAddresses(bool internal = false) override;
 
+    const SigningProvider* GetSigningProvider(const CScript& script) const override;
+
+    bool CanProvide(const CScript& script, SignatureData& sigdata) override;
+
+    uint256 GetID() const override;
+
     // Map from Key ID to key metadata.
     std::map<CKeyID, CKeyMetadata> mapKeyMetadata GUARDED_BY(cs_KeyStore);