Make specifiers support in tuple_join an opt-in

include/fmt/ranges.h

@@ -625,6 +625,13 @@ template <typename Char, typename... T> struct tuple_join_view : detail::view {
 template <typename Char, typename... T>
 using tuple_arg_join = tuple_join_view<Char, T...>;
 
+// Define FMT_TUPLE_JOIN_SPECIFIERS to enable experimental format specifiers
+// support in tuple_join. It is disabled by default because of issues with
+// the dynamic width and precision.
+#ifndef FMT_TUPLE_JOIN_SPECIFIERS
+#  define FMT_TUPLE_JOIN_SPECIFIERS 0
+#endif
+
 template <typename Char, typename... T>
 struct formatter<tuple_join_view<Char, T...>, Char> {
   template <typename ParseContext>
@@ -654,11 +661,13 @@ struct formatter<tuple_join_view<Char, T...>, Char> {
                               std::integral_constant<size_t, N>)
       -> decltype(ctx.begin()) {
     auto end = std::get<sizeof...(T) - N>(formatters_).parse(ctx);
+#if FMT_TUPLE_JOIN_SPECIFIERS
     if (N > 1) {
       auto end1 = do_parse(ctx, std::integral_constant<size_t, N - 1>());
       if (end != end1)
         FMT_THROW(format_error("incompatible format specs for tuple elements"));
     }
+#endif
     return end;
   }
 

test/ranges-test.cc

@@ -225,6 +225,7 @@ TEST(ranges_test, join_tuple) {
   auto t4 = std::tuple<float>(4.0f);
   EXPECT_EQ(fmt::format("{}", fmt::join(t4, "/")), "4");
 
+#  if FMT_TUPLE_JOIN_SPECIFIERS
   // Specs applied to each element.
   auto t5 = std::tuple<int, int, long>(-3, 100, 1);
   EXPECT_EQ(fmt::format("{:+03}", fmt::join(t5, ", ")), "-03, +100, +01");
@@ -237,6 +238,7 @@ TEST(ranges_test, join_tuple) {
   int y = -1;
   auto t7 = std::tuple<int, int&, const int&>(3, y, y);
   EXPECT_EQ(fmt::format("{:03}", fmt::join(t7, ", ")), "003, -01, -01");
+#  endif
 }
 
 TEST(ranges_test, join_initializer_list) {