Extend Rust FFI

Do idiomatic C++ copy and move constructors for a few things, so
wrapping structs' defaults can work.

src/libutil/hash.hh

@@ -44,6 +44,12 @@ struct Hash
        string. */
     Hash(const std::string & s, HashType type = htUnknown);
 
+    Hash(const Hash &) = default;
+
+    Hash(Hash &&) = default;
+
+    Hash & operator = (const Hash &) = default;
+
     void init();
 
     /* Check whether a hash is set. */

src/libutil/rust-ffi.hh

@@ -30,7 +30,10 @@ protected:
 
     // Must not be called directly.
     Value()
-    { }
+    {
+        // Precaution, in case this is used improperly
+        evacuate();
+    }
 
     Value(Value && other)
         : raw(other.raw)
@@ -38,6 +41,19 @@ protected:
         other.evacuate();
     }
 
+    // Not all Rust types are Clone / Copy, but our base Value class needs to
+    // have a copy constructor so that ones which do implement Copy/Clone
+    // can be copied/cloned.
+    Value(const Value & other)
+        : raw(other.raw)
+    {
+    }
+    void operator =(const Value & other)
+    {
+        if (!isEvacuated())
+            drop(this);
+    }
+
     void operator =(Value && other)
     {
         if (!isEvacuated())
@@ -76,6 +92,16 @@ struct Vec : Value<3 * sizeof(void *), drop>
     {
         return ((const T * *) &this->raw)[0];
     }
+
+protected:
+
+    // Must not be called directly.
+    Vec<T, drop>();
+
+    Vec<T, drop>(Vec<T, drop> && other) = default;
+
+    // Delete until we know how to do this properly.
+    Vec<T, drop>(const Vec<T, drop> & other) = delete;
 };
 
 /* A Rust slice. */
@@ -144,7 +170,7 @@ struct Result
         std::exception_ptr * exc;
     };
 
-    Result() : tag(Uninit) { }; // FIXME: remove
+    Result() = delete;
 
     Result(const Result &) = delete;
 
@@ -171,7 +197,7 @@ struct Result
     }
 
     /* Rethrow the wrapped exception or return the wrapped value. */
-    T unwrap()
+    T unwrap() &&
     {
         if (tag == Ok) {
             tag = Uninit;