Clang on MacOS having problems with its includes - c++

Question

I have built from scratch Clang on MacOS and I am having problems with it.
Used following to configure Clang for building:
cmake -G "Unix Makefiles" -DCMAKE_INSTALL_PREFIX=/opt/clang-12 -DCMAKE_BUILD_TYPE=Release -DLLVM_TARGETS_TO_BUILD="AArch64;ARM;X86" -DLLVM_ENABLE_PROJECTS="clang;libcxx;libcxxabi;lldb" ../llvm
This is my test program:
#include <ostream>
#include <algorithm>
int main(int argc, char** argv) {
return 0;
}
OK if compiled with Clang 11.0.3 that ships with XCode clang++ -c test.cc
ERROR if using new Clang 12 (built) /opt/clang-12/bin/clang++ -c test.cc
In file included from test.cc:2:
In file included from /opt/clang-12/bin/../include/c++/v1/ostream:138:
In file included from /opt/clang-12/bin/../include/c++/v1/ios:214:
In file included from /opt/clang-12/bin/../include/c++/v1/iosfwd:95:
/opt/clang-12/bin/../include/c++/v1/wchar.h:119:15: fatal error: 'wchar.h' file not found
#include_next <wchar.h>
^~~~~~~~~
1 error generated.
Depending on what I am trying to include I get different include errors.
➜ tests /opt/clang-12/bin/clang++ -v -c test.cc
clang version 12.0.0 (https://github.com/llvm/llvm-project.git b529c5270c99e0ca18e3cbd9a5f50eb0970e560a)
Target: x86_64-apple-darwin19.6.0
Thread model: posix
InstalledDir: /opt/clang-12/bin
(in-process)
"/opt/clang-12/bin/clang-12" -cc1 -triple x86_64-apple-macosx10.15.0 -Wundef-prefix=TARGET_OS_ -Werror=undef-prefix -Wdeprecated-objc-isa-usage -Werror=deprecated-objc-isa-usage -emit-obj -mrelax-all --mrelax-relocations -disable-free -disable-llvm-verifier -discard-value-names -main-file-name test.cc -mrelocation-model pic -pic-level 2 -mframe-pointer=all -fno-rounding-math -munwind-tables -fcompatibility-qualified-id-block-type-checking -target-cpu penryn -debugger-tuning=lldb -target-linker-version 556.6 -v -resource-dir /opt/clang-12/lib/clang/12.0.0 -stdlib=libc++ -internal-isystem /opt/clang-12/bin/../include/c++/v1 -internal-isystem /usr/include/c++/v1 -internal-isystem /usr/local/include -internal-isystem /opt/clang-12/lib/clang/12.0.0/include -internal-externc-isystem /usr/include -fdeprecated-macro -fdebug-compilation-dir /Users/duddie/Projects/Audio/1voct/1voct_modular/tests -ferror-limit 19 -stack-protector 1 -fblocks -fencode-extended-block-signature -fregister-global-dtors-with-atexit -fgnuc-version=4.2.1 -fcxx-exceptions -fexceptions -fmax-type-align=16 -fcolor-diagnostics -o test.o -x c++ test.cc
clang -cc1 version 12.0.0 based upon LLVM 12.0.0git default target x86_64-apple-darwin19.6.0
ignoring nonexistent directory "/usr/include/c++/v1"
ignoring nonexistent directory "/usr/include"
#include "..." search starts here:
#include <...> search starts here:
/opt/clang-12/bin/../include/c++/v1
/usr/local/include
/opt/clang-12/lib/clang/12.0.0/include
/System/Library/Frameworks (framework directory)
/Library/Frameworks (framework directory)
End of search list.
In file included from test.cc:2:
In file included from /opt/clang-12/bin/../include/c++/v1/ostream:138:
In file included from /opt/clang-12/bin/../include/c++/v1/ios:214:
In file included from /opt/clang-12/bin/../include/c++/v1/iosfwd:95:
/opt/clang-12/bin/../include/c++/v1/wchar.h:119:15: fatal error: 'wchar.h' file not found
#include_next <wchar.h>
^~~~~~~~~
1 error generated.
ERROR if Clang 11.0.3 (XCode) or Clang 12 but target for ARM clang++ -target arm-none-eabi -c test.cc
test.cc:2:10: fatal error: 'ostream' file not found
#include <ostream>
^~~~~~~~~
1 error generated.
Any ideas what am I doing wrong?

Answer 1

Add the following to the shell profile file ~/.bash_profile or ~/.zsh_profile or any other way to set environment variable accessible to the shell you're running it in.
export SDKROOT="/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk"
Verify the correct path to the SDK on your macOS/Xcode version.
Reopen Terminal (sourcing the file may not work reliably).
Then try your compile command again.
/opt/clang-12/bin/clang++ -c test.cc
The Command Line Tools package installs the macOS system headers
inside the macOS SDK. Software that compiles with the installed tools
will search for headers within the macOS SDK provided by either Xcode
at:
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk
or the Command Line Tools at:
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk depending on which
is selected using xcode-select. The command line tools will search the
SDK for system headers by default. However, some software may fail to
build correctly against the SDK and require macOS headers to be
installed in the base system under /usr/include. If you are the
maintainer of such software, we encourage you to update your project
to work with the SDK or file a bug report for issues that are
preventing you from doing so. As a workaround, an extra package is
provided which will install the headers to the base system. In a
future release, this package will no longer be provided. You can find
this package at:
/Library/Developer/CommandLineTools/Packages/macOS_SDK_headers_for_macOS_10.14.pkg
https://developer.apple.com/documentation/xcode-release-notes/xcode-10-release-notes

Answer 2

Probably a more portable one (I found the hint at llvm-project/llvm/utils/lit/lit/util.py:399):
export SDKROOT=$(xcrun --show-sdk-path --sdk macosx)
Also, you can also add -isysroot argument to clang driver to alter the default system root for header searching:
clang++ a.cpp -isysroot $(xcrun --show-sdk-path --sdk macosx)
More details and investigation notes here

Answer 3

For what it's worth, I was able to fix the problem with MacOs Big Sur by doing
export SDKROOT='/Library/Developer/CommandLineTools/SDKs/MacOSX11.1.sdk'