[package] boost/1.76.0: build fails on MacOS Catalina, clang not found

[jakecobb]

Package and Environment Details (include every applicable attribute)

• Package Name/Version: boost/1.76.0
• Operating System+version: MacOS Catalina
• Compiler+version: apple-clang
• Conan version: conan 1.36.0
• Python version: Python 3.8.6

Conan profile (output of conan profile show default or conan profile show <profile> if custom profile is in use)

Configuration for profile default:

[settings]
os=Macos
os_build=Macos
arch=x86_64
arch_build=x86_64
compiler=apple-clang
compiler.version=11.0
compiler.libcxx=libc++
build_type=Release
[options]
[build_requires]
[env]

Steps to reproduce (Include if Applicable)

The build generates an invalid user-config.jam file with this line:

using "clang-darwin" :  :   -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk -arch x86_64 :
<archiver>"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ar" <ranlib>"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ranlib"  ;

Giving an error when it tries to run -isysroot as a command:

warning: toolset clang-darwin initialization:
warning: can not find user-provided command '-isysroot' '/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk' '-arch' 'x86_64'

warning: initialized from /Users/jake/.conan/data/boost/1.76.0/_/_/source/source_subfolder/tools/build/user-config.jam:5

sh: -y: invalid option

Longer log output

boost/1.76.0: 

WARN: replace_in_file didn't find pattern '/* thread_local */' in '/Users/jake/.conan/data/boost/1.76.0/_/_/source/source_subfolder/boost/stacktrace/detail/libbacktrace_impls.hpp' file.
WARN: replace_in_file didn't find pattern '/* static __thread */' in '/Users/jake/.conan/data/boost/1.76.0/_/_/source/source_subfolder/boost/stacktrace/detail/libbacktrace_impls.hpp' file.
boost/1.76.0: WARN: Patching user-config.jam
boost/1.76.0: WARN: 
using zlib : 1.2.11 : <include>"/Users/jake/.conan/data/zlib/1.2.11/_/_/package/0aa7be2d0914b6f3128105e305c90b9cb0cae86d/include" <search>"/Users/jake/.conan/data/zlib/1.2.11/_/_/package/0aa7be2d0914b6f3128105e305c90b9cb0cae86d/lib" <name>z ;
using bzip2 : 1.0.8 : <include>"/Users/jake/.conan/data/bzip2/1.0.8/_/_/package/e26f883c3e136952d830bcdc838898582f2a8d80/include" <search>"/Users/jake/.conan/data/bzip2/1.0.8/_/_/package/e26f883c3e136952d830bcdc838898582f2a8d80/lib" <name>bz2 ;
using "clang-darwin" :  :   -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacO
SX.platform/Developer/SDKs/MacOSX10.15.sdk -arch x86_64 : 
<archiver>"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ar" <ranlib>"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ranlib"  ;
boost/1.76.0: WARN: b2 -q target-os=darwin architecture=x86 address-model=64 binary-format=mach-o abi=sysv --layout=system --user-config=/Users/jake/.conan/data/boost/1.76.0/_/_/source/source_subfolder/tools/build/user-config.jam -sNO_ZLIB=0 -sNO_BZIP2=0 -sNO_LZMA=1 -sNO_ZSTD=1 boost.locale.iconv=on boost.locale.icu=off --disable-icu threading=multi visibility=hidden link=shared variant=debug --with-atomic --with-chrono --with-container --with-context --with-contract --with-coroutine --with-date_time --with-exception --with-filesystem --with-iostreams --with-locale --with-log --with-program_options --with-random --with-regex --with-serialization --with-stacktrace --with-system --with-test --with-thread --with-timer --with-type_erasure --with-wave
 toolset=clang-darwin pch=on -sICONV_PATH=/Users/jake/.conan/data/libiconv/1.16/_/_/package/0aa7be2d0914b6f3128105e305c90b9cb0cae86d linkflags="-stdlib=libc++" cxxflags="-fPIC -stdlib=libc++ -DBOOST_STACKTRACE_ADDR2LINE_LOCATION=/usr/bin/addr2line" install --prefix=/Users/jake/.conan/data/boost/1.76.0/_/_/package/919e25258b36635e511e92527cc7d25469a26c9c -j8 --abbreviate-paths -d0 --debug-configuration --build-dir="/Users/jake/.conan/data/boost/1.76.0/_/_/build/919e25258b36635e511e92527cc7d25469a26c9c"
boost/1.76.0: ERROR: Package '919e25258b36635e511e92527cc7d25469a26c9c' build failed
boost/1.76.0: WARN: Build folder /Users/jake/.conan/data/boost/1.76.0/_/_/build/919e25258b36635e511e92527cc7d25469a26c9c
ERROR: boost/1.76.0: Error in build() method, line 774
	self.run(full_command, run_environment=True)
	ConanException: Error 1 while executing DYLD_LIBRARY_PATH="/Users/jake/.conan/data/bzip2/1.0.8/_/_/package/e26f883c3e136952d830bcdc838898582f2a8d80/lib:/Users/jake/.conan/data/zlib/1.2.11/_/_/package/0aa7be2d0
914b6f3128105e305c90b9cb0cae86d/lib:/Users/jake/.conan/data/libiconv/1.16/_/_/package/0aa7be2d0914b6f3128105e305c90b9cb0cae86d/lib" DYLD_FRAMEWORK_PATH="" b2 -q target-os=darwin architecture=x86 address-model=64 binary-format=mach-o abi=sysv --layout=system --user-config=/Users/jake/.conan/data/boost/1.76.0/_/_/source/source_subfolder/tools/build/user-config.jam -sNO_ZLIB=0 -sNO_BZIP2=0 -sNO_LZMA=1 -sNO_ZSTD=1 boost.locale.iconv=on boost.locale.icu=off --disable-icu threading=multi visibility=hidden link=shared variant=debug --with-atomic --with-chrono --with-container --with-context --with-contract --with-coroutine --with-date_time --with-exception --with-filesystem --with-iostreams --with-locale --with-log --with-program_options --with-random --with-regex --with-serialization --with-stacktrace --with-system --with-test --with-thread --with-timer --with-type_erasure --with-wave toolset=clang-darwin pch=on -sICONV_PATH=/Users/jake/.conan/data/libiconv/1.16/_/_/package/0aa7be2d0914b6f3128105e305c90b9cb0cae86d 
linkflags="-stdlib=libc++" cxxflags="-fPIC -stdlib=libc++ -DBOOST_STACKTRACE_ADDR2LINE_LOCATION=/usr/bin/addr2line" install --prefix=/Users/jake/.conan/data/boost/1.76.0/_/_/package/919e25258b36635e511e92527cc7d25469a26c9c -j8 --abbreviate-paths -d0 --debug-configuration --build-dir="/Users/jake/.conan/data/boost/1.76.0/_/_/build/919e25258b36635e511e92527cc7d25469a26c9c"

It seems like the compiler detection here is failing:

    @property
    def _cxx(self):
        if "CXX" in os.environ:
            return os.environ["CXX"]
        if tools.is_apple_os(self.settings.os) and self.settings.compiler == "apple-clang":
            return tools.XCRun(self.settings).cxx

I'm not sure what the internals of XCRun run exactly, but I do find clang this way:

$ xcrun --find clang
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang
$ xcrun --find clang++
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang++

[jakecobb]

Sorry, let me look into this more, I may have misinterpreted the output.

[jakecobb]

Ok, I've updated the title and description. b2 is not the issue, it's a blank compiler command in the user-config.jam file.

[jakecobb]

I believe this is related to a CMake GUI issue: https://gitlab.kitware.com/cmake/cmake/-/issues/21449

It is setting the CC and CXX environment variables to empty, which means the recipe returns the empty string. It works as expected running cmake from the command line where these variables are not in the environment (typical). The recipe could work around it with:

    @property
    def _cxx(self):
        if os.environ.get("CXX"):
            return os.environ["CXX"]