format: fix error reporting with wide strings

src/format.cpp

@@ -29,9 +29,12 @@ template <typename CharT> using string = std::basic_string<CharT>;
 template <typename CharT> using iterator = typename std::basic_string<CharT>::const_iterator;
 template <typename CharT> using expressions = std::vector<Format::Expression<CharT>>;
 
-std::string invalidCharacter(char c)
+template <typename CharT>
+std::string invalidCharacter(CharT c)
 {
-	return "invalid character '" + boost::lexical_cast<std::string>(c) + "'";
+	return "invalid character '"
+	     + convertString<char, CharT>::apply(boost::lexical_cast<string<CharT>>(c))
+	     + "'";
 }
 
 template <typename CharT>

src/format.h

@@ -21,12 +21,12 @@
 #ifndef NCMPCPP_HAVE_FORMAT_H
 #define NCMPCPP_HAVE_FORMAT_H
 
-#include <boost/locale/encoding_utf.hpp>
 #include <boost/variant.hpp>
 
 #include "menu.h"
 #include "song.h"
 #include "strbuffer.h"
+#include "utility/functional.h"
 #include "utility/wide_string.h"
 
 namespace Format {
@@ -125,7 +125,7 @@ struct Printer: boost::static_visitor<bool>
 		StringT tags;
 		if (m_song != nullptr)
 		{
-			tags = convertString<std::is_same<char, CharT>::value, std::string>::apply(
+			tags = convertString<CharT, char>::apply(
 				m_song->getTags(st.function())
 			);
 		}
@@ -177,20 +177,6 @@ struct Printer: boost::static_visitor<bool>
 	}
 
 private:
-	// convert string to appropriate type
-	template <bool AreSame, typename ValueT>
-	struct convertString {
-		static const StringT &apply(const ValueT &s) {
-			return s;
-		}
-	};
-	template <typename ValueT>
-	struct convertString<false, ValueT> {
-		static StringT apply(const ValueT &s) {
-			return boost::locale::conv::utf_to_utf<CharT>(s);
-		}
-	};
-
 	// generic version for streams (buffers, menus)
 	template <typename ValueT, typename OutputStreamT>
 	struct output_ {

src/utility/functional.h

@@ -21,6 +21,7 @@
 #ifndef NCMPCPP_UTILITY_FUNCTIONAL_H
 #define NCMPCPP_UTILITY_FUNCTIONAL_H
 
+#include <boost/locale/encoding_utf.hpp>
 #include <utility>
 
 // identity function object
@@ -34,4 +35,23 @@ struct id_
 	}
 };
 
+// convert string to appropriate type
+template <typename TargetT, typename SourceT>
+struct convertString
+{
+	static std::basic_string<TargetT> apply(const std::basic_string<SourceT> &s)
+	{
+		return boost::locale::conv::utf_to_utf<TargetT>(s);
+	}
+};
+template <typename TargetT>
+struct convertString<TargetT, TargetT>
+{
+	static const std::basic_string<TargetT> &apply(const std::basic_string<TargetT> &s)
+	{
+		return s;
+	}
+};
+
+
 #endif // NCMPCPP_UTILITY_FUNCTIONAL_H