Fix type safety when using custom formatters (#394)

test/custom-formatter-test.cc

@@ -45,10 +45,13 @@ class CustomPrintfArgFormatter :
   }
 };
 
-std::string custom_vformat(const char *format_str, fmt::format_args args) {
+typedef fmt::BasicFormatter<char, CustomArgFormatter> CustomFormatter;
+
+std::string custom_vformat(const char *format_str,
+                           fmt::basic_format_args<CustomFormatter> args) {
   fmt::MemoryWriter writer;
   // Pass custom argument formatter as a template arg to BasicFormatter.
-  fmt::BasicFormatter<char, CustomArgFormatter> formatter(args, writer);
+  CustomFormatter formatter(args, writer);
   formatter.format(format_str);
   return writer.str();
 }
@@ -59,9 +62,14 @@ std::string custom_format(const char *format_str, const Args & ... args) {
   return custom_vformat(format_str, va);
 }
 
-std::string custom_vsprintf(const char* format_str, fmt::format_args args) {
+typedef fmt::PrintfFormatter<char, CustomPrintfArgFormatter>
+  CustomPrintfFormatter;
+
+std::string custom_vsprintf(
+    const char* format_str,
+    fmt::basic_format_args<CustomPrintfFormatter> args) {
   fmt::MemoryWriter writer;
-  fmt::PrintfFormatter<char, CustomPrintfArgFormatter> formatter(args, writer);
+  CustomPrintfFormatter formatter(args, writer);
   formatter.format(format_str);
   return writer.str();
 }

test/format-test.cc

@@ -1633,16 +1633,19 @@ class MockArgFormatter :
   MOCK_METHOD1(visit_int, void (int value));
 };
 
-void vcustom_format(const char *format_str, fmt::format_args args) {
+typedef fmt::BasicFormatter<char, MockArgFormatter> CustomFormatter;
+
+void custom_vformat(const char *format_str,
+                    fmt::basic_format_args<CustomFormatter> args) {
   fmt::MemoryWriter writer;
-  fmt::BasicFormatter<char, MockArgFormatter> formatter(args, writer);
+  CustomFormatter formatter(args, writer);
   formatter.format(format_str);
 }
 
 template <typename... Args>
 void custom_format(const char *format_str, const Args & ... args) {
   auto va = fmt::make_format_args<fmt::BasicFormatter<char>>(args...);
-  return vcustom_format(format_str, va);
+  return custom_vformat(format_str, va);
 }
 
 TEST(FormatTest, CustomArgFormatter) {

test/ostream-test.cc

@@ -67,7 +67,7 @@ struct TestArgFormatter : fmt::BasicArgFormatter<TestArgFormatter, char> {
 TEST(OStreamTest, CustomArg) {
   fmt::MemoryWriter writer;
   typedef fmt::BasicFormatter<char, TestArgFormatter> Formatter;
-  Formatter formatter(fmt::format_args(), writer);
+  Formatter formatter(fmt::basic_format_args<Formatter>(), writer);
   fmt::FormatSpec spec;
   TestArgFormatter af(formatter, spec, "}");
   af.visit(fmt::internal::MakeArg<Formatter>(TestEnum()));