libc++ woes with Xcode 14

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Created Dec ’22

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We are writing server-side C++ code that runs on Linux in production but some of the developers use Macs. We standardized on Clang 14 (or the equivalent Apple Clang) and libc++ as the runtime library. The dev environment is either VSCode or CLion.

I have clang 14 installed via Xcode, and even though it also installed libc++ 14, it chooses to use libc++ 13 instead (from a different directory).

% printf "#include <version>\nint main(){}" | /usr/bin/clang++ -std=c++20 -stdlib=libc++ -E -x c++ -dM - | grep _LIBCPP_VERSION
#define _LIBCPP_VERSION 13000

Some investigation (grep output trimmed:

% grep -R -H "#define _LIBCPP_VERSION" --include=__config --exclude-dir=System / 2>/dev/null

/Library/Developer/CommandLineTools/usr/include/c++/v1/__config:#define _LIBCPP_VERSION 14000
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__config:#define _LIBCPP_VERSION 13000
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/__config:#define _LIBCPP_VERSION 14000

So 14.0 is installed, but the directory with 13.0 is selected:

% printf "#include <__config>\nint main(){}" | /usr/bin/clang++ -std=c++20 -stdlib=libc++ -E -x c++ - | grep "2 3"
# 14 "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1/__config" 2 3

Let's see what else clang has to say:

% /usr/bin/clang++ -v
Apple clang version 14.0.0 (clang-1400.0.29.102)
Target: arm64-apple-darwin21.6.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin

% clang++ -print-search-dirs
programs: =/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
libraries: =/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/14.0.0

So for some reason, clang takes the libraries from one directory, but the standard headers from another.

I could try using -nostdlibinc and specifying the "correct" include directory explicitly, but I am not sure what the side effects will be and I'd rather understand what's going on.

Boost

Answer 1

Alex-O OP

Dec ’22

More: Clang apparently looks in both the platform and the toolchain directories:

% printf "#include <version>\nint main(){}" | /usr/bin/clang++ -std=c++20 -stdlib=libc++ -x c++ --verbose -
Apple clang version 14.0.0 (clang-1400.0.29.102)
Target: arm64-apple-darwin21.6.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
 "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang" -cc1 -triple arm64-apple-macosx12.0.0 -Wundef-prefix=TARGET_OS_ -Wdeprecated-objc-isa-usage -Werror=deprecated-objc-isa-usage -Werror=implicit-function-declaration -emit-obj -mrelax-all --mrelax-relocations -disable-free -clear-ast-before-backend -disable-llvm-verifier -discard-value-names -main-file-name - -mrelocation-model pic -pic-level 2 -mframe-pointer=non-leaf -fno-strict-return -fno-rounding-math -funwind-tables=2 -fobjc-msgsend-selector-stubs -target-sdk-version=12.3 -fvisibility-inlines-hidden-static-local-var -target-cpu apple-m1 -target-feature +v8.5a -target-feature +fp-armv8 -target-feature +neon -target-feature +crc -target-feature +crypto -target-feature +dotprod -target-feature +fp16fml -target-feature +ras -target-feature +lse -target-feature +rdm -target-feature +rcpc -target-feature +zcm -target-feature +zcz -target-feature +fullfp16 -target-feature +sm4 -target-feature +sha3 -target-feature +sha2 -target-feature +aes -target-abi darwinpcs -fallow-half-arguments-and-returns -debugger-tuning=lldb -target-linker-version 819.6 -v -resource-dir /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/14.0.0 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk -I/usr/local/include -stdlib=libc++ -internal-isystem /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1 -internal-isystem /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/local/include -internal-isystem /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/14.0.0/include -internal-externc-isystem /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include -internal-externc-isystem /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include -Wno-reorder-init-list -Wno-implicit-int-float-conversion -Wno-c99-designator -Wno-final-dtor-non-final-class -Wno-extra-semi-stmt -Wno-misleading-indentation -Wno-quoted-include-in-framework-header -Wno-implicit-fallthrough -Wno-enum-enum-conversion -Wno-enum-float-conversion -Wno-elaborated-enum-base -Wno-reserved-identifier -Wno-gnu-folding-constant -Wno-cast-function-type -Wno-bitwise-instead-of-logical -std=c++20 -fdeprecated-macro -fdebug-compilation-dir=/Users/<redacted>/work/local/cppversion -ferror-limit 19 -stack-protector 1 -fstack-check -mdarwin-stkchk-strong-link -fblocks -fencode-extended-block-signature -fregister-global-dtors-with-atexit -fgnuc-version=4.2.1 -fno-cxx-modules -fno-implicit-modules -fcxx-exceptions -fexceptions -fmax-type-align=16 -fcommon -fcolor-diagnostics -clang-vendor-feature=+messageToSelfInClassMethodIdReturnType -clang-vendor-feature=+disableInferNewAvailabilityFromInit -clang-vendor-feature=+disableNonDependentMemberExprInCurrentInstantiation -fno-odr-hash-protocols -clang-vendor-feature=+enableAggressiveVLAFolding -clang-vendor-feature=+revert09abecef7bbf -clang-vendor-feature=+thisNoAlignAttr -clang-vendor-feature=+thisNoNullAttr -mllvm -disable-aligned-alloc-awareness=1 -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o /var/folders/cw/72b4rmqd4pq7z8fblm3nwgjh0000gq/T/--9f4670.o -x c++ -
clang -cc1 version 14.0.0 (clang-1400.0.29.102) default target arm64-apple-darwin21.6.0
ignoring nonexistent directory "/usr/local/include"
ignoring nonexistent directory "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/local/include"
ignoring nonexistent directory "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/Library/Frameworks"
#include "..." search starts here:
#include <...> search starts here:
 /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/c++/v1
 /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/14.0.0/include
 /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include
 /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include
 /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks (framework directory)
End of search list.
 "/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld" -demangle -lto_library /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/libLTO.dylib -no_deduplicate -dynamic -arch arm64 -platform_version macos 12.0.0 12.3 -syslibroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk -o a.out -L/usr/local/lib /var/folders/cw/72b4rmqd4pq7z8fblm3nwgjh0000gq/T/--9f4670.o -lc++ -lSystem /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/14.0.0/lib/darwin/libclang_rt.osx.a

Is there a way to change those defaults?

0

Answer 2

Alex-O OP

Dec ’22

Specifically, libc++ 14 adds support for the C++20 std::format

0