From 81eb9f952bdf49eb9e62fe7297d162970e83e889 Mon Sep 17 00:00:00 2001
From: Michael Jones <jonesmz@users.noreply.github.com>
Date: Mon, 13 Jul 2026 10:04:33 -0500
Subject: [PATCH] Guard use of char8_t in concepts.hpp with if
 defined(__cpp_char8_t)

---
 include/boost/parser/concepts.hpp                      |  2 ++
 include/boost/parser/detail/text/concepts.hpp          | 10 ++++++----
 .../boost/parser/detail/text/transcode_iterator.hpp    |  8 ++++++--
 include/boost/parser/detail/text/transcode_view.hpp    |  4 ++++
 4 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/include/boost/parser/concepts.hpp b/include/boost/parser/concepts.hpp
index 296ca92f..cb770515 100644
--- a/include/boost/parser/concepts.hpp
+++ b/include/boost/parser/concepts.hpp
@@ -22,7 +22,9 @@ namespace boost { namespace parser {
     concept code_unit =
         std::same_as<std::remove_cv_t<T>, char> ||
         std::same_as<std::remove_cv_t<T>, wchar_t> ||
+#if defined(__cpp_char8_t)
         std::same_as<std::remove_cv_t<T>, char8_t> ||
+#endif
         std::same_as<std::remove_cv_t<T>, char16_t>||
         std::same_as<std::remove_cv_t<T>, char32_t>;
 
diff --git a/include/boost/parser/detail/text/concepts.hpp b/include/boost/parser/detail/text/concepts.hpp
index 2913dda4..3c025d9d 100644
--- a/include/boost/parser/detail/text/concepts.hpp
+++ b/include/boost/parser/detail/text/concepts.hpp
@@ -27,11 +27,13 @@ namespace boost::parser::detail { namespace text { BOOST_PARSER_DETAIL_TEXT_NAME
 #endif
 
     template<typename T, format F>
-    concept code_unit = (std::same_as<T, char8_t> && F == format::utf8) ||
+    concept code_unit = (std::same_as<T, char> && F == format::utf8) ||
+                        (std::same_as<T, wchar_t> && F == wchar_t_format) ||
+#if defined(__cpp_char8_t)
+                        (std::same_as<T, char8_t> && F == format::utf8) ||
+#endif
                         (std::same_as<T, char16_t> && F == format::utf16) ||
-                        (std::same_as<T, char32_t> && F == format::utf32) ||
-                        (std::same_as<T, char> && F == format::utf8) ||
-                        (std::same_as<T, wchar_t> && F == wchar_t_format);
+                        (std::same_as<T, char32_t> && F == format::utf32);
 
     template<typename T>
     concept utf8_code_unit = code_unit<T, format::utf8>;
diff --git a/include/boost/parser/detail/text/transcode_iterator.hpp b/include/boost/parser/detail/text/transcode_iterator.hpp
index f979b5a4..ab3f0896 100644
--- a/include/boost/parser/detail/text/transcode_iterator.hpp
+++ b/include/boost/parser/detail/text/transcode_iterator.hpp
@@ -976,7 +976,7 @@ namespace boost::parser::detail { namespace text {
 
     /** An out iterator that converts UTF-32 to UTF-8. */
 #if BOOST_PARSER_DETAIL_TEXT_USE_CONCEPTS
-    template<std::output_iterator<char8_t> Iter>
+    template<std::output_iterator<char8_type> Iter>
 #else
     template<typename Iter>
 #endif
@@ -1501,7 +1501,7 @@ namespace boost::parser::detail { namespace text {
 
     /** An out iterator that converts UTF-16 to UTF-8. */
 #if BOOST_PARSER_DETAIL_TEXT_USE_CONCEPTS
-    template<std::output_iterator<char8_t> Iter>
+    template<std::output_iterator<char8_type> Iter>
 #else
     template<typename Iter>
 #endif
@@ -2295,11 +2295,13 @@ namespace boost::parser::detail { namespace text { BOOST_PARSER_DETAIL_TEXT_NAME
 
 namespace boost::parser::detail { namespace text { BOOST_PARSER_DETAIL_TEXT_NAMESPACE_V2 {
 
+#if defined(__cpp_char8_t)
     template<std::output_iterator<char8_t> O>
     constexpr utf_32_to_8_out_iterator<O> utf_32_to_8_out(O it)
     {
         return utf_32_to_8_out_iterator<O>(it);
     }
+#endif
 
     template<std::output_iterator<char32_t> O>
     constexpr utf_8_to_32_out_iterator<O> utf_8_to_32_out(O it)
@@ -2319,11 +2321,13 @@ namespace boost::parser::detail { namespace text { BOOST_PARSER_DETAIL_TEXT_NAME
         return utf_16_to_32_out_iterator<O>(it);
     }
 
+#if defined(__cpp_char8_t)
     template<std::output_iterator<char8_t> O>
     constexpr utf_16_to_8_out_iterator<O> utf_16_to_8_out(O it)
     {
         return utf_16_to_8_out_iterator<O>(it);
     }
+#endif
 
     template<std::output_iterator<char16_t> O>
     constexpr utf_8_to_16_out_iterator<O> utf_8_to_16_out(O it)
diff --git a/include/boost/parser/detail/text/transcode_view.hpp b/include/boost/parser/detail/text/transcode_view.hpp
index 275a5273..44d24570 100644
--- a/include/boost/parser/detail/text/transcode_view.hpp
+++ b/include/boost/parser/detail/text/transcode_view.hpp
@@ -375,8 +375,10 @@ namespace boost::parser::detail { namespace text {
     };
 
 #if BOOST_PARSER_DETAIL_TEXT_USE_CONCEPTS
+#if defined(__cpp_char8_t)
     template<class R>
     char8_view(R &&) -> char8_view<detail::all_t<R>>;
+#endif
     template<class R>
     char16_view(R &&) -> char16_view<detail::all_t<R>>;
     template<class R>
@@ -413,8 +415,10 @@ namespace boost::parser::detail { namespace text {
         template<class T>
         constexpr bool is_charn_view = false;
 #if BOOST_PARSER_DETAIL_TEXT_USE_CONCEPTS
+#if defined(__cpp_char8_t)
         template<class V>
         constexpr bool is_charn_view<char8_view<V>> = true;
+#endif
 #endif
         template<class V>
         constexpr bool is_charn_view<char16_view<V>> = true;