Workaround a bug in gcc

include/fmt/core.h

@@ -1360,6 +1360,10 @@ using buffer_context =
 using format_context = buffer_context<char>;
 using wformat_context = buffer_context<wchar_t>;
 
+// Workaround a bug in gcc: https://stackoverflow.com/q/62767544/471164.
+#define FMT_BUFFER_CONTEXT(Char) \
+  basic_format_context<std::back_insert_iterator<detail::buffer<Char>>, Char>
+
 /**
   \rst
   An array of references to arguments. It can be implicitly converted into
@@ -1768,9 +1772,9 @@ std::basic_string<Char> vformat(
 std::string vformat(string_view format_str, format_args args);
 
 template <typename Char>
-typename buffer_context<Char>::iterator vformat_to(
+typename FMT_BUFFER_CONTEXT(Char)::iterator vformat_to(
     buffer<Char>& buf, basic_string_view<Char> format_str,
-    basic_format_args<buffer_context<type_identity_t<Char>>> args);
+    basic_format_args<FMT_BUFFER_CONTEXT(type_identity_t<Char>)> args);
 
 template <typename Char, typename Args,
           FMT_ENABLE_IF(!std::is_same<Char, char>::value)>

include/fmt/format.h

@@ -3482,9 +3482,9 @@ extern template int snprintf_float<long double>(long double value,
 
 template <typename S, typename Char = char_t<S>,
           FMT_ENABLE_IF(detail::is_string<S>::value)>
-inline typename buffer_context<Char>::iterator vformat_to(
+inline typename FMT_BUFFER_CONTEXT(Char)::iterator vformat_to(
     detail::buffer<Char>& buf, const S& format_str,
-    basic_format_args<buffer_context<type_identity_t<Char>>> args) {
+    basic_format_args<FMT_BUFFER_CONTEXT(type_identity_t<Char>)> args) {
   return detail::vformat_to(buf, to_string_view(format_str), args);
 }
 

src/format.cc

@@ -44,8 +44,9 @@ template FMT_API char detail::decimal_point_impl(locale_ref);
 
 template FMT_API void detail::buffer<char>::append(const char*, const char*);
 
-template FMT_API format_context::iterator detail::vformat_to(
-    detail::buffer<char>&, string_view, basic_format_args<format_context>);
+template FMT_API FMT_BUFFER_CONTEXT(char)::iterator detail::vformat_to(
+    detail::buffer<char>&, string_view,
+    basic_format_args<FMT_BUFFER_CONTEXT(char)>);
 
 template FMT_API int detail::snprintf_float(double, int, detail::float_specs,
                                             detail::buffer<char>&);