fmt::join support FMT_COMPILE (#2720)

include/fmt/format.h

@@ -2818,8 +2818,8 @@ struct formatter<join_view<It, Sentinel, Char>, Char> {
   }
 
   template <typename FormatContext>
-  auto format(const join_view<It, Sentinel, Char>& value, FormatContext& ctx)
-      -> decltype(ctx.out()) {
+  auto format(const join_view<It, Sentinel, Char>& value,
+              FormatContext& ctx) const -> decltype(ctx.out()) {
     auto it = value.begin;
     auto out = ctx.out();
     if (it != value.end) {

include/fmt/ostream.h

@@ -86,7 +86,7 @@ struct fallback_formatter<T, Char, enable_if_t<is_streamable<T, Char>::value>>
   using formatter<basic_string_view<Char>, Char>::parse;
 
   template <typename OutputIt>
-  auto format(const T& value, basic_format_context<OutputIt, Char>& ctx)
+  auto format(const T& value, basic_format_context<OutputIt, Char>& ctx) const
       -> OutputIt {
     auto buffer = basic_memory_buffer<Char>();
     format_value(buffer, value, ctx.locale());
@@ -96,7 +96,7 @@ struct fallback_formatter<T, Char, enable_if_t<is_streamable<T, Char>::value>>
 
   // DEPRECATED!
   template <typename OutputIt>
-  auto format(const T& value, basic_printf_context<OutputIt, Char>& ctx)
+  auto format(const T& value, basic_printf_context<OutputIt, Char>& ctx) const
       -> OutputIt {
     auto buffer = basic_memory_buffer<Char>();
     format_value(buffer, value, ctx.locale());

test/compile-test.cc

@@ -201,6 +201,11 @@ TEST(compile_test, named) {
 #  endif
 }
 
+TEST(compile_test, join) {
+  unsigned char data[] = {0x1, 0x2, 0xaf};
+  EXPECT_EQ("0102af", fmt::format(FMT_COMPILE("{:02x}"), fmt::join(data, "")));
+}
+
 TEST(compile_test, format_to) {
   char buf[8];
   auto end = fmt::format_to(buf, FMT_COMPILE("{}"), 42);