Multiple errors on gcc 8.2/8.3

[phprus]

gcc: 8.2.1
os: openSUSE 15.1

First of error:

[ 21%] Building CXX object test/CMakeFiles/locale-test.dir/locale-test.cc.o
/home/phprus/tmp/fmt/fmt-7.1.0/test/locale-test.cc: In member function ‘virtual void LocaleTest_Format_Test::TestBody()’:
/home/phprus/tmp/fmt/fmt-7.1.0/test/locale-test.cc:59:61: error: no matching function for call to ‘format_to(std::back_insert_iterator<std::__cxx11::basic_string<char> >, std::locale&, const char [5], int)’
   fmt::format_to(std::back_inserter(s), loc, "{:L}", 1234567);
                                                             ^
In file included from /home/phprus/tmp/fmt/fmt-7.1.0/include/fmt/format.h:44,
                 from /home/phprus/tmp/fmt/fmt-7.1.0/include/fmt/locale.h:13,
                 from /home/phprus/tmp/fmt/fmt-7.1.0/test/locale-test.cc:8:
/home/phprus/tmp/fmt/fmt-7.1.0/include/fmt/core.h:1994:13: note: candidate: ‘template<class OutputIt, class S, class ... Args, bool enable> typename std::enable_if<enable, OutputIt>::type fmt::v7::format_to(OutputIt, const S&, Args&& ...)’
 inline auto format_to(OutputIt out, const S& format_str, Args&&... args) ->
             ^~~~~~~~~
/home/phprus/tmp/fmt/fmt-7.1.0/include/fmt/core.h:1994:13: note:   template argument deduction/substitution failed:
/home/phprus/tmp/fmt/fmt-7.1.0/include/fmt/core.h:1993:74: error: no type named ‘type’ in ‘struct fmt::v7::detail::char_t_impl<std::locale, void>’
           bool enable = detail::is_output_iterator<OutputIt, char_t<S>>::value>
                                                                          ^~~~~
/home/phprus/tmp/fmt/fmt-7.1.0/include/fmt/core.h:1993:74: error: could not convert template argument ‘<expression error>’ from ‘<type error>’ to ‘bool’
In file included from /home/phprus/tmp/fmt/fmt-7.1.0/include/fmt/locale.h:13,
                 from /home/phprus/tmp/fmt/fmt-7.1.0/test/locale-test.cc:8:
/home/phprus/tmp/fmt/fmt-7.1.0/include/fmt/format.h:3822:48: note: candidate: ‘template<class S, class ... Args, long unsigned int SIZE, class Char> typename fmt::v7::buffer_context<Char>::iterator fmt::v7::format_to(fmt::v7::basic_memory_buffer<Char, SIZE>&, const S&, Args&& ...)’
 inline typename buffer_context<Char>::iterator format_to(
                                                ^~~~~~~~~
/home/phprus/tmp/fmt/fmt-7.1.0/include/fmt/format.h:3822:48: note:   template argument deduction/substitution failed:
/home/phprus/tmp/fmt/fmt-7.1.0/test/locale-test.cc:59:61: note:   ‘std::back_insert_iterator<std::__cxx11::basic_string<char> >’ is not derived from ‘fmt::v7::basic_memory_buffer<Char, SIZE>’
   fmt::format_to(std::back_inserter(s), loc, "{:L}", 1234567);
                                                             ^
In file included from /home/phprus/tmp/fmt/fmt-7.1.0/test/locale-test.cc:8:
/home/phprus/tmp/fmt/fmt-7.1.0/include/fmt/locale.h:56:17: note: candidate: ‘template<class OutputIt, class S, class ... Args, class Char, typename std::enable_if<fmt::v7::detail::is_output_iterator<OutputIt, Char>::value, int>::type <anonymous> > OutputIt fmt::v7::format_to(OutputIt, const std::locale&, const S&, Args&& ...)’
 inline OutputIt format_to(OutputIt out, const std::locale& loc,
                 ^~~~~~~~~
/home/phprus/tmp/fmt/fmt-7.1.0/include/fmt/locale.h:56:17: note:   template argument deduction/substitution failed:
In file included from /home/phprus/tmp/fmt/fmt-7.1.0/include/fmt/format.h:44,
                 from /home/phprus/tmp/fmt/fmt-7.1.0/include/fmt/locale.h:13,
                 from /home/phprus/tmp/fmt/fmt-7.1.0/test/locale-test.cc:8:
/home/phprus/tmp/fmt/fmt-7.1.0/include/fmt/core.h:277:62: error: no type named ‘type’ in ‘struct std::enable_if<false, int>’
 #define FMT_ENABLE_IF(...) enable_if_t<(__VA_ARGS__), int> = 0
                                                              ^
/home/phprus/tmp/fmt/fmt-7.1.0/include/fmt/locale.h:55:11: note: in expansion of macro ‘FMT_ENABLE_IF’
           FMT_ENABLE_IF(detail::is_output_iterator<OutputIt, Char>::value)>
           ^~~~~~~~~~~~~

[vitaut]

Looks like the same gcc 8 bug as in #1949.

[phprus]

Yes...
Possible patch:

Index: fmt/include/fmt/locale.h
===================================================================
--- fmt.orig/include/fmt/locale.h
+++ fmt/include/fmt/locale.h
@@ -51,10 +51,10 @@ inline OutputIt vformat_to(
 }
 
 template <typename OutputIt, typename S, typename... Args,
-          typename Char = char_t<S>,
-          FMT_ENABLE_IF(detail::is_output_iterator<OutputIt, Char>::value)>
-inline OutputIt format_to(OutputIt out, const std::locale& loc,
-                          const S& format_str, Args&&... args) {
+          bool enable = detail::is_output_iterator<OutputIt, char_t<S>>::value>
+inline auto format_to(OutputIt out, const std::locale& loc,
+                          const S& format_str, Args&&... args) ->
+    typename std::enable_if<enable, OutputIt>::type {
   const auto& vargs = fmt::make_args_checked<Args...>(format_str, args...);
   return vformat_to(out, loc, to_string_view(format_str), vargs);
 }
Index: fmt/include/fmt/core.h
===================================================================
--- fmt.orig/include/fmt/core.h
+++ fmt/include/fmt/core.h
@@ -1968,10 +1968,11 @@ inline void vprint_mojibake(std::FILE*, 
 // GCC 8 and earlier cannot handle std::back_insert_iterator<Container> with
 // vformat_to<ArgFormatter>(...) overload, so SFINAE on iterator type instead.
 template <typename OutputIt, typename S, typename Char = char_t<S>,
-          FMT_ENABLE_IF(detail::is_output_iterator<OutputIt, Char>::value)>
-OutputIt vformat_to(
+          bool enable = detail::is_output_iterator<OutputIt, Char>::value>
+auto vformat_to(
     OutputIt out, const S& format_str,
-    basic_format_args<buffer_context<type_identity_t<Char>>> args) {
+    basic_format_args<buffer_context<type_identity_t<Char>>> args) ->
+    typename std::enable_if<enable, OutputIt>::type {
   decltype(detail::get_buffer<Char>(out)) buf(detail::get_buffer_init(out));
   detail::vformat_to(buf, to_string_view(format_str), args);
   return detail::get_iterator(buf);
@@ -2023,10 +2024,11 @@ inline format_to_n_result<OutputIt> vfor
  \endrst
  */
 template <typename OutputIt, typename S, typename... Args,
-          FMT_ENABLE_IF(detail::is_output_iterator<OutputIt, char_t<S>>::value)>
-inline format_to_n_result<OutputIt> format_to_n(OutputIt out, size_t n,
+          bool enable = detail::is_output_iterator<OutputIt, char_t<S>>::value>
+inline auto format_to_n(OutputIt out, size_t n,
                                                 const S& format_str,
-                                                const Args&... args) {
+                                                const Args&... args) ->
+    typename std::enable_if<enable, format_to_n_result<OutputIt>>::type {
   const auto& vargs = fmt::make_args_checked<Args...>(format_str, args...);
   return vformat_to_n(out, n, to_string_view(format_str), vargs);
 }
Index: fmt/include/fmt/color.h
===================================================================
--- fmt.orig/include/fmt/color.h
+++ fmt/include/fmt/color.h
@@ -589,10 +589,11 @@ OutputIt vformat_to(
   \endrst
 */
 template <typename OutputIt, typename S, typename... Args,
-          FMT_ENABLE_IF(detail::is_output_iterator<OutputIt, char_t<S>>::value&&
+          bool enable = (detail::is_output_iterator<OutputIt, char_t<S>>::value&&
                             detail::is_string<S>::value)>
-inline OutputIt format_to(OutputIt out, const text_style& ts,
-                          const S& format_str, Args&&... args) {
+inline auto format_to(OutputIt out, const text_style& ts,
+                          const S& format_str, Args&&... args) ->
+    typename std::enable_if<enable, OutputIt>::type {
   return vformat_to(out, ts, to_string_view(format_str),
                     fmt::make_args_checked<Args...>(format_str, args...));
 }
Index: fmt/include/fmt/compile.h
===================================================================
--- fmt.orig/include/fmt/compile.h
+++ fmt/include/fmt/compile.h
@@ -667,14 +667,15 @@ OutputIt format_to(OutputIt out, const S
   return format_to(out, compiled, args...);
 }
 
-template <typename OutputIt, typename CompiledFormat, typename... Args,
-          FMT_ENABLE_IF(detail::is_output_iterator<
-                        OutputIt, typename CompiledFormat::char_type>::value&&
-                            std::is_base_of<detail::basic_compiled_format,
-                                            CompiledFormat>::value)>
-format_to_n_result<OutputIt> format_to_n(OutputIt out, size_t n,
-                                         const CompiledFormat& cf,
-                                         const Args&... args) {
+template <typename OutputIt, typename CompiledFormat, typename... Args>
+typename std::enable_if<(detail::is_output_iterator<
+                         OutputIt, typename CompiledFormat::char_type>::value&&
+                             std::is_base_of<detail::basic_compiled_format,
+                                             CompiledFormat>::value),
+                        format_to_n_result<OutputIt>
+>::type format_to_n(OutputIt out, size_t n,
+                    const CompiledFormat& cf,
+                    const Args&... args) {
   auto it =
       format_to(detail::truncating_iterator<OutputIt>(out, n), cf, args...);
   return {it.base(), it.count()};

[vitaut]

Could you submit a PR?