Use underlying type for enums in is_signed/is_unsigned. #199
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This was referenced Sep 5, 2025
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The problem you have here, is that |
With clang >= 21, using is_signed/is_unsigned with "small" enums (having an underlying type smaller than an int) results in strong error, after being reported as warnings for years (see boostorg#171). Since boost::is_signed/is_unsigned differs explicitly from the std one, and can return "true" for enums (contrary to the std one), keep this boost behavior and implement a special check for enums. This allows in particular boost::lexical_cast to keep working when converting non-scoped enums from int to strings with clang >= 21, see boostorg/lexical_cast#87).
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@jzmaddock I changed a bit the definition, to now use underlying_type only for enums. |
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Recent versions of clang made -Wenum-constexpr-conversion errors into a
hard error, as was announced several versions ago.
Boost type_traits has two instances where it attempts to convert
out-of-range enum values, leading to errors similar to:
In file included from ../src/lib/dhcpsrv/csv_lease_file6.cc:9:
In file included from ../src/lib/dhcpsrv/dhcpsrv_log.h:11:
In file included from ../src/lib/log/macros.h:10:
In file included from ../src/lib/log/logger.h:19:
In file included from ../src/lib/log/log_formatter.h:19:
In file included from /usr/local/include/boost/lexical_cast.hpp:33:
In file included from /usr/local/include/boost/lexical_cast/try_lexical_convert.hpp:31:
In file included from /usr/local/include/boost/lexical_cast/detail/converter_numeric.hpp:31:
In file included from /usr/local/include/boost/type_traits/make_unsigned.hpp:14:
/usr/local/include/boost/type_traits/is_signed.hpp:37:25: error: in-class initializer for static data member is not a constant expression
37 | static const no_cv_t minus_one = (static_cast<no_cv_t>(-1));
| ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/include/boost/type_traits/is_signed.hpp:45:60: note: in instantiation of template class 'boost::detail::is_signed_values<isc::dhcp::Lease::Type>' requested here
45 | BOOST_STATIC_CONSTANT(bool, value = (!(::boost::detail::is_signed_values<T>::minus_one > boost::detail::is_signed_values<T>::zero)));
| ^
/usr/local/include/boost/config/detail/suffix.hpp:410:72: note: expanded from macro 'BOOST_STATIC_CONSTANT'
410 | # define BOOST_STATIC_CONSTANT(type, assignment) static const type assignment
| ^
/usr/local/include/boost/type_traits/is_signed.hpp:74:40: note: in instantiation of template class 'boost::detail::is_signed_helper<isc::dhcp::Lease::Type>' requested here
74 | BOOST_STATIC_CONSTANT(bool, value = type::value);
| ^
/usr/local/include/boost/config/detail/suffix.hpp:410:72: note: expanded from macro 'BOOST_STATIC_CONSTANT'
410 | # define BOOST_STATIC_CONSTANT(type, assignment) static const type assignment
| ^
/usr/local/include/boost/type_traits/is_signed.hpp:79:85: note: in instantiation of template class 'boost::detail::is_signed_impl<isc::dhcp::Lease::Type>' requested here
79 | template <class T> struct is_signed : public integral_constant<bool, boost::detail::is_signed_impl<T>::value> {};
| ^
/usr/local/include/boost/lexical_cast/detail/converter_lexical_streams.hpp:315:44: note: in instantiation of template class 'boost::is_signed<isc::dhcp::Lease::Type>' requested here
315 | typename boost::enable_if_c<boost::is_signed<Type>::value && !boost::is_enum<Type>::value, bool>::type
| ^
/usr/local/include/boost/lexical_cast/detail/converter_lexical.hpp:449:67: note: while substituting deduced template arguments into function template 'stream_in' [with Type = isc::dhcp::Lease::Type]
449 | -> decltype(std::declval<optimized_src_stream&>().stream_in(std::declval<lcast::exact<T>>()), optimized_src_stream{});
| ^
/usr/local/include/boost/lexical_cast/detail/converter_lexical.hpp:454:46: note: while substituting explicitly-specified template arguments into function template 'detect_type'
454 | using from_src_stream = decltype(detect_type<Source>(1));
| ^
/usr/local/include/boost/lexical_cast/try_lexical_convert.hpp:67:20: note: in instantiation of template class 'boost::detail::lexical_converter_impl<std::string, isc::dhcp::Lease::Type>' requested here
67 | return caster_type::try_convert(arg, result);
| ^
/usr/local/include/boost/lexical_cast.hpp:42:41: note: in instantiation of function template specialization 'boost::conversion::detail::try_lexical_convert<std::string, isc::dhcp::Lease::Type>' requested here
42 | if (!boost::conversion::detail::try_lexical_convert(arg, result)) {
| ^
../src/lib/util/csv_file.h:243:34: note: in instantiation of function template specialization 'boost::lexical_cast<std::string, isc::dhcp::Lease::Type>' requested here
243 | values_[at] = boost::lexical_cast<std::string>(value);
| ^
../src/lib/dhcpsrv/csv_lease_file6.cc:54:9: note: in instantiation of function template specialization 'isc::util::CSVRow::writeAt<isc::dhcp::Lease::Type>' requested here
54 | row.writeAt(getColumnIndex("lease_type"), lease.type_);
| ^
/usr/local/include/boost/type_traits/is_signed.hpp:37:38: note: integer value -1 is outside the valid range of values [0, 3] for the enumeration type 'Type'
37 | static const no_cv_t minus_one = (static_cast<no_cv_t>(-1));
| ^
This is while compiling net/kea, but other users of boost type traits
may also have the same issue.
There is an upstream bug report at:
boostorg/type_traits#202
and an outstanding pull request at:
boostorg/type_traits#199
Apply the latter as a diff, to work around the problem. Bump
PORTREVISION to make dependents recompile.
PR: 292071
Approved by: fluffy (maintainer)
MFH: 2025Q4
freebsd-git
pushed a commit
to freebsd/freebsd-ports
that referenced
this pull request
Jan 1, 2026
Recent versions of clang made -Wenum-constexpr-conversion errors into a
hard error, as was announced several versions ago.
Boost type_traits has two instances where it attempts to convert
out-of-range enum values, leading to errors similar to:
In file included from ../src/lib/dhcpsrv/csv_lease_file6.cc:9:
In file included from ../src/lib/dhcpsrv/dhcpsrv_log.h:11:
In file included from ../src/lib/log/macros.h:10:
In file included from ../src/lib/log/logger.h:19:
In file included from ../src/lib/log/log_formatter.h:19:
In file included from /usr/local/include/boost/lexical_cast.hpp:33:
In file included from /usr/local/include/boost/lexical_cast/try_lexical_convert.hpp:31:
In file included from /usr/local/include/boost/lexical_cast/detail/converter_numeric.hpp:31:
In file included from /usr/local/include/boost/type_traits/make_unsigned.hpp:14:
/usr/local/include/boost/type_traits/is_signed.hpp:37:25: error: in-class initializer for static data member is not a constant expression
37 | static const no_cv_t minus_one = (static_cast<no_cv_t>(-1));
| ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/include/boost/type_traits/is_signed.hpp:45:60: note: in instantiation of template class 'boost::detail::is_signed_values<isc::dhcp::Lease::Type>' requested here
45 | BOOST_STATIC_CONSTANT(bool, value = (!(::boost::detail::is_signed_values<T>::minus_one > boost::detail::is_signed_values<T>::zero)));
| ^
/usr/local/include/boost/config/detail/suffix.hpp:410:72: note: expanded from macro 'BOOST_STATIC_CONSTANT'
410 | # define BOOST_STATIC_CONSTANT(type, assignment) static const type assignment
| ^
/usr/local/include/boost/type_traits/is_signed.hpp:74:40: note: in instantiation of template class 'boost::detail::is_signed_helper<isc::dhcp::Lease::Type>' requested here
74 | BOOST_STATIC_CONSTANT(bool, value = type::value);
| ^
/usr/local/include/boost/config/detail/suffix.hpp:410:72: note: expanded from macro 'BOOST_STATIC_CONSTANT'
410 | # define BOOST_STATIC_CONSTANT(type, assignment) static const type assignment
| ^
/usr/local/include/boost/type_traits/is_signed.hpp:79:85: note: in instantiation of template class 'boost::detail::is_signed_impl<isc::dhcp::Lease::Type>' requested here
79 | template <class T> struct is_signed : public integral_constant<bool, boost::detail::is_signed_impl<T>::value> {};
| ^
/usr/local/include/boost/lexical_cast/detail/converter_lexical_streams.hpp:315:44: note: in instantiation of template class 'boost::is_signed<isc::dhcp::Lease::Type>' requested here
315 | typename boost::enable_if_c<boost::is_signed<Type>::value && !boost::is_enum<Type>::value, bool>::type
| ^
/usr/local/include/boost/lexical_cast/detail/converter_lexical.hpp:449:67: note: while substituting deduced template arguments into function template 'stream_in' [with Type = isc::dhcp::Lease::Type]
449 | -> decltype(std::declval<optimized_src_stream&>().stream_in(std::declval<lcast::exact<T>>()), optimized_src_stream{});
| ^
/usr/local/include/boost/lexical_cast/detail/converter_lexical.hpp:454:46: note: while substituting explicitly-specified template arguments into function template 'detect_type'
454 | using from_src_stream = decltype(detect_type<Source>(1));
| ^
/usr/local/include/boost/lexical_cast/try_lexical_convert.hpp:67:20: note: in instantiation of template class 'boost::detail::lexical_converter_impl<std::string, isc::dhcp::Lease::Type>' requested here
67 | return caster_type::try_convert(arg, result);
| ^
/usr/local/include/boost/lexical_cast.hpp:42:41: note: in instantiation of function template specialization 'boost::conversion::detail::try_lexical_convert<std::string, isc::dhcp::Lease::Type>' requested here
42 | if (!boost::conversion::detail::try_lexical_convert(arg, result)) {
| ^
../src/lib/util/csv_file.h:243:34: note: in instantiation of function template specialization 'boost::lexical_cast<std::string, isc::dhcp::Lease::Type>' requested here
243 | values_[at] = boost::lexical_cast<std::string>(value);
| ^
../src/lib/dhcpsrv/csv_lease_file6.cc:54:9: note: in instantiation of function template specialization 'isc::util::CSVRow::writeAt<isc::dhcp::Lease::Type>' requested here
54 | row.writeAt(getColumnIndex("lease_type"), lease.type_);
| ^
/usr/local/include/boost/type_traits/is_signed.hpp:37:38: note: integer value -1 is outside the valid range of values [0, 3] for the enumeration type 'Type'
37 | static const no_cv_t minus_one = (static_cast<no_cv_t>(-1));
| ^
This is while compiling net/kea, but other users of boost type traits
may also have the same issue.
There is an upstream bug report at:
boostorg/type_traits#202
and an outstanding pull request at:
boostorg/type_traits#199
Apply the latter as a diff, to work around the problem. Bump
PORTREVISION to make dependents recompile.
PR: 292071
Approved by: fluffy (maintainer)
MFH: 2025Q4
(cherry picked from commit ab93476)
fluffykhv
pushed a commit
to fluffykhv/freebsd-ports-boost
that referenced
this pull request
Jan 1, 2026
Recent versions of clang made -Wenum-constexpr-conversion errors into a
hard error, as was announced several versions ago.
Boost type_traits has two instances where it attempts to convert
out-of-range enum values, leading to errors similar to:
In file included from ../src/lib/dhcpsrv/csv_lease_file6.cc:9:
In file included from ../src/lib/dhcpsrv/dhcpsrv_log.h:11:
In file included from ../src/lib/log/macros.h:10:
In file included from ../src/lib/log/logger.h:19:
In file included from ../src/lib/log/log_formatter.h:19:
In file included from /usr/local/include/boost/lexical_cast.hpp:33:
In file included from /usr/local/include/boost/lexical_cast/try_lexical_convert.hpp:31:
In file included from /usr/local/include/boost/lexical_cast/detail/converter_numeric.hpp:31:
In file included from /usr/local/include/boost/type_traits/make_unsigned.hpp:14:
/usr/local/include/boost/type_traits/is_signed.hpp:37:25: error: in-class initializer for static data member is not a constant expression
37 | static const no_cv_t minus_one = (static_cast<no_cv_t>(-1));
| ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/include/boost/type_traits/is_signed.hpp:45:60: note: in instantiation of template class 'boost::detail::is_signed_values<isc::dhcp::Lease::Type>' requested here
45 | BOOST_STATIC_CONSTANT(bool, value = (!(::boost::detail::is_signed_values<T>::minus_one > boost::detail::is_signed_values<T>::zero)));
| ^
/usr/local/include/boost/config/detail/suffix.hpp:410:72: note: expanded from macro 'BOOST_STATIC_CONSTANT'
410 | # define BOOST_STATIC_CONSTANT(type, assignment) static const type assignment
| ^
/usr/local/include/boost/type_traits/is_signed.hpp:74:40: note: in instantiation of template class 'boost::detail::is_signed_helper<isc::dhcp::Lease::Type>' requested here
74 | BOOST_STATIC_CONSTANT(bool, value = type::value);
| ^
/usr/local/include/boost/config/detail/suffix.hpp:410:72: note: expanded from macro 'BOOST_STATIC_CONSTANT'
410 | # define BOOST_STATIC_CONSTANT(type, assignment) static const type assignment
| ^
/usr/local/include/boost/type_traits/is_signed.hpp:79:85: note: in instantiation of template class 'boost::detail::is_signed_impl<isc::dhcp::Lease::Type>' requested here
79 | template <class T> struct is_signed : public integral_constant<bool, boost::detail::is_signed_impl<T>::value> {};
| ^
/usr/local/include/boost/lexical_cast/detail/converter_lexical_streams.hpp:315:44: note: in instantiation of template class 'boost::is_signed<isc::dhcp::Lease::Type>' requested here
315 | typename boost::enable_if_c<boost::is_signed<Type>::value && !boost::is_enum<Type>::value, bool>::type
| ^
/usr/local/include/boost/lexical_cast/detail/converter_lexical.hpp:449:67: note: while substituting deduced template arguments into function template 'stream_in' [with Type = isc::dhcp::Lease::Type]
449 | -> decltype(std::declval<optimized_src_stream&>().stream_in(std::declval<lcast::exact<T>>()), optimized_src_stream{});
| ^
/usr/local/include/boost/lexical_cast/detail/converter_lexical.hpp:454:46: note: while substituting explicitly-specified template arguments into function template 'detect_type'
454 | using from_src_stream = decltype(detect_type<Source>(1));
| ^
/usr/local/include/boost/lexical_cast/try_lexical_convert.hpp:67:20: note: in instantiation of template class 'boost::detail::lexical_converter_impl<std::string, isc::dhcp::Lease::Type>' requested here
67 | return caster_type::try_convert(arg, result);
| ^
/usr/local/include/boost/lexical_cast.hpp:42:41: note: in instantiation of function template specialization 'boost::conversion::detail::try_lexical_convert<std::string, isc::dhcp::Lease::Type>' requested here
42 | if (!boost::conversion::detail::try_lexical_convert(arg, result)) {
| ^
../src/lib/util/csv_file.h:243:34: note: in instantiation of function template specialization 'boost::lexical_cast<std::string, isc::dhcp::Lease::Type>' requested here
243 | values_[at] = boost::lexical_cast<std::string>(value);
| ^
../src/lib/dhcpsrv/csv_lease_file6.cc:54:9: note: in instantiation of function template specialization 'isc::util::CSVRow::writeAt<isc::dhcp::Lease::Type>' requested here
54 | row.writeAt(getColumnIndex("lease_type"), lease.type_);
| ^
/usr/local/include/boost/type_traits/is_signed.hpp:37:38: note: integer value -1 is outside the valid range of values [0, 3] for the enumeration type 'Type'
37 | static const no_cv_t minus_one = (static_cast<no_cv_t>(-1));
| ^
This is while compiling net/kea, but other users of boost type traits
may also have the same issue.
There is an upstream bug report at:
boostorg/type_traits#202
and an outstanding pull request at:
boostorg/type_traits#199
Apply the latter as a diff, to work around the problem. Bump
PORTREVISION to make dependents recompile.
PR: 292071
Approved by: fluffy (maintainer)
MFH: 2025Q4
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With clang >= 21, using is_signed/is_unsigned with "small" enums (having an underlying type smaller than an int) results in strong error, after being reported as warnings for years (see #171).
Since boost::is_signed/is_unsigned differs explicitly from the std one, and can return "true" for enums (contrary to the std one), keep this boost behavior and implement a special check for enums.
This allows in particular boost::lexical_cast to keep working when converting non-scoped enums from int to strings with clang >= 21, see boostorg/lexical_cast#87).