Add purpose arg to Wallet::getAddress

Also make all arguments to getAddress required and document args at call sites.

src/interfaces/wallet.cpp

@@ -152,7 +152,10 @@ public:
     {
         return m_wallet.DelAddressBook(dest);
     }
-    bool getAddress(const CTxDestination& dest, std::string* name, isminetype* is_mine) override
+    bool getAddress(const CTxDestination& dest,
+        std::string* name,
+        isminetype* is_mine,
+        std::string* purpose) override
     {
         LOCK(m_wallet.cs_wallet);
         auto it = m_wallet.mapAddressBook.find(dest);
@@ -165,6 +168,9 @@ public:
         if (is_mine) {
             *is_mine = IsMine(m_wallet, dest);
         }
+        if (purpose) {
+            *purpose = it->second.purpose;
+        }
         return true;
     }
     std::vector<WalletAddress> getAddresses() override

src/interfaces/wallet.h

@@ -99,8 +99,9 @@ public:
 
     //! Look up address in wallet, return whether exists.
     virtual bool getAddress(const CTxDestination& dest,
-        std::string* name = nullptr,
-        isminetype* is_mine = nullptr) = 0;
+        std::string* name,
+        isminetype* is_mine,
+        std::string* purpose) = 0;
 
     //! Get wallet address list.
     virtual std::vector<WalletAddress> getAddresses() = 0;