Merge bitcoin/bitcoin#25594: refactor: Return BResult from restoreWallet

fa475e9c79 refactor: Return BResult from restoreWallet (MacroFake)
fa8de09edc Prepare BResult for non-copyable types (MacroFake)

Pull request description:

  This avoids the `error` in-out param (and if `warnings` is added to `BResult`, it will avoid passing that in-out param as well).

  Also, as it is needed for this change, prepare `BResult` for non-copyable types.

ACKs for top commit:
  w0xlt:
    reACK fa475e9c79
  ryanofsky:
    Code review ACK fa475e9c79. Changes since last review were replacing auto with explicit type and splitting commits

Tree-SHA512: 46350883572f13721ddd198f5dfb88d2fa58ebcbda416f74da3563ea15c920fb1e6ff30558526a4ac91c36c21e6afe27751a4e51b7b8bcbcbe805209f4e9014b

src/util/result.h

@@ -6,6 +6,7 @@
 #define BITCOIN_UTIL_RESULT_H
 
 #include <util/translation.h>
+
 #include <variant>
 
 /*
@@ -18,9 +19,9 @@ private:
     std::variant<bilingual_str, T> m_variant;
 
 public:
-    BResult() : m_variant(Untranslated("")) {}
-    BResult(const T& _obj) : m_variant(_obj) {}
-    BResult(const bilingual_str& error) : m_variant(error) {}
+    BResult() : m_variant{Untranslated("")} {}
+    BResult(T obj) : m_variant{std::move(obj)} {}
+    BResult(bilingual_str error) : m_variant{std::move(error)} {}
 
     /* Whether the function succeeded or not */
     bool HasRes() const { return std::holds_alternative<T>(m_variant); }
@@ -30,6 +31,11 @@ public:
         assert(HasRes());
         return std::get<T>(m_variant);
     }
+    T ReleaseObj()
+    {
+        assert(HasRes());
+        return std::move(std::get<T>(m_variant));
+    }
 
     /* In case of failure, the error cause */
     const bilingual_str& GetError() const {