From 805e84f6795d286019ed865016f2703239c6b9fe Mon Sep 17 00:00:00 2001
From: Barry Revzin <barry.revzin@gmail.com>
Date: Mon, 19 Jun 2023 13:36:58 -0500
Subject: [PATCH] Adding guards around if constexpr

---
 include/fmt/core.h | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/include/fmt/core.h b/include/fmt/core.h
index 86dcd7a3..5fe659ff 100644
--- a/include/fmt/core.h
+++ b/include/fmt/core.h
@@ -1539,8 +1539,10 @@ constexpr auto encode_types() -> unsigned long long {
          (encode_types<Context, Args...>() << packed_arg_bits);
 }
 
+#if defined(__cpp_if_constexpr)
 // This type is intentionally undefined, only used for errors
 template <typename T, typename Char> struct type_is_unformattable_for;
+#endif
 
 template <bool PACKED, typename Context, typename T, FMT_ENABLE_IF(PACKED)>
 FMT_CONSTEXPR FMT_INLINE auto make_arg(T& val) -> value<Context> {
@@ -1548,9 +1550,11 @@ FMT_CONSTEXPR FMT_INLINE auto make_arg(T& val) -> value<Context> {
 
   constexpr bool formattable_char =
       !std::is_same<arg_type, unformattable_char>::value;
+#if defined(__cpp_if_constexpr)
   if constexpr (not formattable_char) {
     type_is_unformattable_for<T, typename Context::char_type> _;
   }
+#endif
   static_assert(formattable_char, "Mixing character types is disallowed.");
 
   // Formatting of arbitrary pointers is disallowed. If you want to format a
@@ -1558,16 +1562,20 @@ FMT_CONSTEXPR FMT_INLINE auto make_arg(T& val) -> value<Context> {
   // formatting of `[const] volatile char*` printed as bool by iostreams.
   constexpr bool formattable_pointer =
       !std::is_same<arg_type, unformattable_pointer>::value;
+#if defined(__cpp_if_constexpr)
   if constexpr (not formattable_pointer) {
     type_is_unformattable_for<T, typename Context::char_type> _;
   }
+#endif
   static_assert(formattable_pointer,
                 "Formatting of non-void pointers is disallowed.");
 
   constexpr bool formattable = !std::is_same<arg_type, unformattable>::value;
+#if defined(__cpp_if_constexpr)
   if constexpr (not formattable) {
     type_is_unformattable_for<T, typename Context::char_type> _;
   }
+#endif
   static_assert(
       formattable,
       "Cannot format an argument. To make type T formattable provide a "
@@ -2532,6 +2540,7 @@ FMT_CONSTEXPR auto parse_format_specs(ParseContext& ctx)
       mapped_type_constant<T, context>::value != type::custom_type,
       decltype(arg_mapper<context>().map(std::declval<const T&>())),
       typename strip_named_arg<T>::type>;
+#if defined(__cpp_if_constexpr)
   if constexpr (std::is_default_constructible_v<
                     formatter<mapped_type, char_type>>) {
     return formatter<mapped_type, char_type>().parse(ctx);
@@ -2539,6 +2548,9 @@ FMT_CONSTEXPR auto parse_format_specs(ParseContext& ctx)
     type_is_unformattable_for<T, char_type> _;
     return ctx.begin();
   }
+#else
+  return formatter<mapped_type, char_type>().parse(ctx);
+#endif
 }
 
 // Checks char specs and returns true iff the presentation type is char-like.