From b3a133e196f4abc6c371ec13d69c9340da8041c2 Mon Sep 17 00:00:00 2001
From: Flamefire <git@grundis.de>
Date: Sat, 4 Jan 2025 12:48:27 +0100
Subject: [PATCH 1/2] Add reproducer for Clang < 15 bug with string_view &
 C++11 char types

---
 test/sv_conversion_test.cpp | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/test/sv_conversion_test.cpp b/test/sv_conversion_test.cpp
index f9cec64e..50ea714a 100644
--- a/test/sv_conversion_test.cpp
+++ b/test/sv_conversion_test.cpp
@@ -29,6 +29,29 @@ boost::core::string_view f( boost::core::string_view const& str )
     return str;
 }
 
+template<typename Char>
+boost::core::basic_string_view<Char> f( boost::core::basic_string_view<Char> const& str )
+{
+    return str;
+}
+
+template<typename Char>
+void subtest()
+{
+    std::basic_string<Char> s1( 3, Char('1') );
+    s1[1] = Char('2');
+    s1[2] = Char('3');
+
+    std::basic_string<Char> s2 = f<Char>( s1 );
+    BOOST_TEST( s1 == s2 );
+
+#if ! (defined(BOOST_CLANG) && BOOST_CLANG_VERSION < 150000)
+    // leads to undefined symbols in Clang < 15: https://github.com/llvm/llvm-project/issues/55560
+    std::basic_string<Char> s3( (f<Char>( s1 )) );
+    BOOST_TEST( s1 == s3 );
+#endif
+}
+
 int main()
 {
     {
@@ -62,5 +85,15 @@ int main()
 
 #endif
 
+#if !defined(BOOST_NO_CXX11_CHAR16_T)
+    subtest<char16_t>();
+#endif
+#if !defined(BOOST_NO_CXX11_CHAR32_T)
+    subtest<char32_t>();
+#endif
+#if defined(__cpp_char8_t) && __cpp_char8_t >= 201811L
+    subtest<char8_t>();
+#endif
+
     return boost::report_errors();
 }

From e5e0c5028d792fd9e472e25b5426d686720e0c9d Mon Sep 17 00:00:00 2001
From: Alexander Grund <Flamefire@users.noreply.github.com>
Date: Sat, 4 Jan 2025 11:58:34 +0100
Subject: [PATCH 2/2] Workaround clang bug

Clang < 15 has a bug in c++-20 mode where using the `std::basic_string` constructor taking a pointer and size leads to an undefined symbol `M_construct` when used with Unicode char types

Avoid this by using the range constructor.
---
 include/boost/core/detail/string_view.hpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/boost/core/detail/string_view.hpp b/include/boost/core/detail/string_view.hpp
index 8f9ab355..85fd3538 100644
--- a/include/boost/core/detail/string_view.hpp
+++ b/include/boost/core/detail/string_view.hpp
@@ -422,7 +422,7 @@ template<class Ch> class basic_string_view
 
     template<class A> operator std::basic_string<Ch, std::char_traits<Ch>, A>() const
     {
-        return std::basic_string<Ch, std::char_traits<Ch>, A>( data(), size() );
+        return std::basic_string<Ch, std::char_traits<Ch>, A>( begin(), end() );
     }
 
 #if !defined(BOOST_NO_CXX17_HDR_STRING_VIEW)