clang: fix -Wrange-loop-analysis warnings

contrib/epee/src/byte_slice.cpp

@@ -151,7 +151,7 @@ namespace epee
     : byte_slice()
   {
     std::size_t space_needed = 0;
-    for (const auto source : sources)
+    for (const auto& source : sources)
       space_needed += source.size();
 
     if (space_needed)
@@ -160,7 +160,7 @@ namespace epee
       span<std::uint8_t> out{reinterpret_cast<std::uint8_t*>(storage.get() + 1), space_needed};
       portion_ = {out.data(), out.size()};
 
-      for (const auto source : sources)
+      for (const auto& source : sources)
       {
         std::memcpy(out.data(), source.data(), source.size());
         if (out.remove_prefix(source.size()) < source.size())

src/serialization/json_object.h

@@ -365,7 +365,7 @@ inline typename std::enable_if<sfinae::is_vector_like<Vec>::value, void>::type t
   static_assert(!std::is_same<value_type, unsigned char>::value, "encoding an array of unsigned char is faster as hex");
 
   dest.StartArray();
-  for (const auto& t : vec)
+  for (auto t : vec)
     toJsonValue(dest, t);
   dest.EndArray();
 }

tests/unit_tests/json_serialization.cpp

@@ -51,7 +51,7 @@ namespace test
             if (!cryptonote::find_tx_extra_field_by_type(extra_fields, key_field))
                 throw std::runtime_error{"invalid transaction"};
 
-            for (auto const& input : boost::adaptors::index(source.vout))
+            for (auto const input : boost::adaptors::index(source.vout))
             {
                 source_amount += input.value().amount;
                 auto const& key = boost::get<cryptonote::txout_to_key>(input.value().target);