Fix collision with global convert function (#425)

fmt/format.h

@@ -1155,7 +1155,9 @@ struct ConvertToIntImpl2<T, true> {
 
 template<typename T>
 struct ConvertToInt {
-  enum { enable_conversion = sizeof(convert(get<T>())) == sizeof(Yes) };
+  enum {
+    enable_conversion = sizeof(fmt::internal::convert(get<T>())) == sizeof(Yes)
+  };
   enum { value = ConvertToIntImpl2<T, enable_conversion>::value };
 };
 

test/format-test.cc

@@ -1653,3 +1653,11 @@ FMT_VARIADIC(void, custom_format, const char *)
 TEST(FormatTest, CustomArgFormatter) {
   custom_format("{}", 42);
 }
+
+void convert(int);
+
+// Check if there is no collision with convert function in the global namespace.
+TEST(FormatTest, ConvertCollision) {
+  fmt::format("{}", 42);
+}
+