Error in static_assert for std::ranges::contiguous_range for rust::Slice on MacOS #1535
Description
We are running into a compilation error in CI on MacOS with cxx version 1.0.160 with c++20.
The failure happens in this static_assert with the following error:
In file included from /Applications/Xcode_15.4.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__iterator/concepts.h:34:
/Applications/Xcode_15.4.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__memory/pointer_traits.h:118:22: error: implicit instantiation of undefined template 'std::__pointer_traits_element_type<rust::Slice<const unsigned char>::iterator>'
typedef typename __pointer_traits_element_type<pointer>::type element_type;
^
/Applications/Xcode_15.4.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__memory/pointer_traits.h:182:20: note: in instantiation of template class 'std::pointer_traits<rust::Slice<const unsigned char>::iterator>' requested here
decltype((void)pointer_traits<_Pointer>::to_address(std::declval<const _Pointer&>()))
^
/Applications/Xcode_15.4.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__memory/pointer_traits.h:195:59: note: during template argument deduction for class template partial specialization '_HasToAddress<_Pointer, decltype((void)pointer_traits<_Pointer>::to_address(std::declval<const _Pointer &>()))>' [with _Pointer = rust::Slice<const unsigned char>::iterator]
static const bool value = _HasArrow<_Pointer>::value || _HasToAddress<_Pointer>::value;
^
/Applications/Xcode_15.4.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__memory/pointer_traits.h:195:59: note: in instantiation of template class 'std::_HasToAddress<rust::Slice<const unsigned char>::iterator>' requested here
/Applications/Xcode_15.4.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__type_traits/conjunction.h:27:32: note: in instantiation of template class 'std::_IsFancyPointer<rust::Slice<const unsigned char>::iterator>' requested here
__expand_to_true<__enable_if_t<_Pred::value>...> __and_helper(int);
^
/Applications/Xcode_15.4.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__type_traits/conjunction.h:38:39: note: while substituting explicitly-specified template arguments into function template '__and_helper'
using _And _LIBCPP_NODEBUG = decltype(std::__and_helper<_Pred...>(0));
^
/Applications/Xcode_15.4.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__memory/pointer_traits.h:200:5: note: (skipping 4 contexts in backtrace; use -ftemplate-backtrace-limit=0 to see all)
_And<is_class<_Pointer>, _IsFancyPointer<_Pointer> >::value
^
/Applications/Xcode_15.4.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__iterator/concepts.h:193:7: note: in instantiation of requirement here
{ _VSTD::to_address(__i) } -> same_as<add_pointer_t<iter_reference_t<_Ip>>>;
^~~~~~~~~~~~~~~~~~~~~~
/Applications/Xcode_15.4.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__config:897:17: note: expanded from macro '_VSTD'
# define _VSTD std
^
/Applications/Xcode_15.4.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__iterator/concepts.h:192:3: note: while substituting template arguments into constraint expression here
requires(const _Ip& __i) {
^~~~~~~~~~~~~~~~~~~~~~~~~~
/Applications/Xcode_15.4.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__ranges/concepts.h:122:5: note: while checking the satisfaction of concept 'contiguous_iterator<rust::Slice<const unsigned char>::iterator>' requested here
contiguous_iterator<iterator_t<_Tp>> &&
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Applications/Xcode_15.4.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__ranges/concepts.h:122:5: note: while substituting template arguments into constraint expression here
contiguous_iterator<iterator_t<_Tp>> &&
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Users/runner/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/cxx-1.0.160/src/../include/cxx.h:282:15: note: while checking the satisfaction of concept 'contiguous_range<rust::Slice<const unsigned char>>' requested here
static_assert(std::ranges::contiguous_range<rust::Slice<const uint8_t>>);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/Applications/Xcode_15.4.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__memory/pointer_traits.h:38:8: note: template is declared here
struct __pointer_traits_element_type;
^
1 error generated.
error: failed to run custom build command for `cxx v1.0.160`
error occurred in cc-rs: command did not execute successfully (status code exit status: 1): env -u IPHONEOS_DEPLOYMENT_TARGET LC_ALL="C" "c++" "-O2" "-ffunction-sections" "-fdata-sections" "-fPIC" "-gdwarf-2" "-fno-omit-frame-pointer" "--target=arm64-apple-macosx" "-mmacosx-version-min=14.5" "-std=c++20" "-Wall" "-Wextra" "-o" "/Users/runner/work/miri/miri/target/debug/build/cxx-efb7933382949e42/out/c16f17691ff6f04b-cxx.o" "-c" "/Users/runner/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/cxx-1.0.160/src/cxx.cc"
Here is the full log from CI in case it's needed.
This failing CI run uses the exact same MacOS image (macos-14-arm64, Version: 20250630.1634) that was used in a successful cxx CI run a few hours ago. The most significant difference seems to be using C++20, since the failing static_assert only applies to this/higher versions. From what I can tell from this ci.yml, the combination of MacOS + C++20 isn't tested in cxx CI, which is likely why the problem didn't show up there.