Macos 26 CI fails on ostream_iterator with -std=c++23 #206
Description
I am working on lttoolbox update for MacPorts. Current version lttoolbox 3.8.2 builds on macos 14 and 15 CI, but fails on macos 26 CI in acx.cc:
https://github.com/Dave-Allured/macports-ports/actions/runs/19790870027. The compiler is AppleClang 17.0.0. Flag -std=c++23 is included in the macos 26 build. Here is a very brief log excerpt. See full log file at above link for more details.
cd /opt/local/var/macports/build/lttoolbox-63ad2f6c/work/build/lttoolbox && /usr/bin/clang++ -DHAVE_GETOPT_LONG -DLTTOOLBOX_EXPORTS -DPACKAGE_VERSION=\"3.8.2\" -DSIZET_NOT_CSTDINT -D_GNU_SOURCE -D_POSIX_C_SOURCE=200112 -Dlttoolbox_EXPORTS -I/opt/local/include/libxml2 -I/opt/local/include/utf8cpp -I/opt/local/var/macports/build/lttoolbox-63ad2f6c/work/lttoolbox-3.8.2 -I/opt/local/var/macports/build/lttoolbox-63ad2f6c/work/lttoolbox-3.8.2/lttoolbox -pipe -Os -DNDEBUG -I/opt/local/include -stdlib=libc++ -isysroot/Library/Developer/CommandLineTools/SDKs/MacOSX26.sdk -Wall -Wextra -Wno-missing-field-initializers -Wno-deprecated -Wno-unused-parameter -fPIC -Wno-unused-result -flto -fvisibility-inlines-hidden -std=c++23 -arch arm64 -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX26.sdk -mmacosx-version-min=26.0 -fPIC -MD -MT lttoolbox/CMakeFiles/lttoolbox.dir/acx.cc.o -MF CMakeFiles/lttoolbox.dir/acx.cc.o.d -o CMakeFiles/lttoolbox.dir/acx.cc.o -c /opt/local/var/macports/build/lttoolbox-63ad2f6c/work/lttoolbox-3.8.2/lttoolbox/acx.cc
In file included from /opt/local/var/macports/build/lttoolbox-63ad2f6c/work/lttoolbox-3.8.2/lttoolbox/acx.cc:17:
In file included from /opt/local/var/macports/build/lttoolbox-63ad2f6c/work/lttoolbox-3.8.2/lttoolbox/acx.h:20:
In file included from /opt/local/var/macports/build/lttoolbox-63ad2f6c/work/lttoolbox-3.8.2/lttoolbox/sorted_vector.hpp:25:
In file included from /Library/Developer/CommandLineTools/SDKs/MacOSX26.sdk/usr/include/c++/v1/iterator:698:
/Library/Developer/CommandLineTools/SDKs/MacOSX26.sdk/usr/include/c++/v1/__iterator/ostream_iterator.h:62:20: error: invalid operands to binary expression ('ostream_type' (aka 'basic_ostream<char, std::char_traits<char>>') and 'const char')
62 | *__out_stream_ << __value;
| ~~~~~~~~~~~~~~ ^ ~~~~~~~
Github Copilot suggests:
- Summary — why it fails on macOS 26 and not macOS 15
- The compiler error originates from uses of operator<< / ostream_iterator in lttoolbox (acx.cc → sorted_vector.hpp → std::iterator headers). Newer Clang/libc++ shipped with macOS 26 has stricter overload resolution and/or different template/overload candidates than the toolchain on macOS 15. Code that relied on permissive implicit conversions (e.g. passing a char or a C-string where the ostream_iterator's value_type or the stream operator overloads expected a different type) now fails to compile.
- In short: newer standard library + stricter overload resolution exposes a type mismatch when the code writes values/delimiters to an ostream via ostream_iterator. Older SDKs accepted it; the macOS 26 toolchain does not.
I do not understand C++ well enough to see the correct fix for this code. I will try downgrading the C++ standard to get this build to pass. Please let me know if a better fix is created.