[cfe-dev] clang built from source in Mac OSX 10.14 with apple-clang/Xcode missing stdlib from include search path

[Jens Jorgensen via cfe-dev]

I recently cloned llvm from git and did a build of clang on my Macbook
(OSX 10.14.6). I have Xcode (11.0) installed and built using Xcode's
included apple-clang. The build worked fine but when I went to compile
my project I got an error where it was trying to #include a stdlib
header file. I'm not really sure but I think this is because in MacOS
Mojave by default the os has System Integrity Protection enabled which
among other things prevents modification to at least some locations
under /usr (root user unable to ln -s ... /usr/include/c++, tried that).
So Xcode does not install or symlink the standard library headers into
/usr/include. apple-clang as installed already includes the installed
stdlib header directories in its search path. Looking at the current git
source I don't see a way to build clang to set a directory to look in
for the stdlib. I did try -DGCC_INSTALL_PREFIX=... and that did not do
the trick, apparently because it does not end up keeping that path for
searching include <...>.

I made a local git branch and made some changes to allow me to build a
clang++ that includes the installed location in the include search path
but before I log a bug/submit a change for review I wanted to see what
constraints around this would end up being acceptable. Should the cmake
scripts automatically pick this up by default on OSX if building with
the Xcode-supplied compiler? Should it be structured/would it be useful
to introduce a top-level #define to set this default stdlib search path
in clang/include/clang/Config/config.h.cmake?

For reference, here's a comparison on a test.cpp file containing simple
#include <string>:

~/src/clang-build-20190828/bin/clang++  -v -c /tmp/test.cpp
clang version 10.0.0 (https://github.com/llvm/llvm-project.git
92ed86d239cdd6ed97dae3084f6537088da88677)
Target: x86_64-apple-darwin18.7.0
Thread model: posix
InstalledDir: /Users/user/src/clang-build-20190828/bin
 "/Users/user/src/clang-build-20190828/bin/clang-10" -cc1 -triple
x86_64-apple-macosx10.14.0 -Wdeprecated-objc-isa-usage
-Werror=deprecated-objc-isa-usage -emit-obj -mrelax-all -disable-free
-disable-llvm-verifier -discard-value-names -main-file-name test.cpp
-mrelocation-model pic -pic-level 2 -mthread-model posix
-mframe-pointer=all -masm-verbose -munwind-tables -target-cpu penryn
-dwarf-column-info -debugger-tuning=lldb -ggnu-pubnames
-target-linker-version 450.3 -v -coverage-notes-file
/Users/user/src/llvm-project/test.gcno -resource-dir
/Users/user/src/clang-build-20190828/lib/clang/10.0.0 -stdlib=libc++
-internal-isystem
/Users/user/src/clang-build-20190828/bin/../include/c++/v1
-internal-isystem /usr/include/c++/v1 -internal-isystem
/usr/local/include -internal-isystem
/Users/user/src/clang-build-20190828/lib/clang/10.0.0/include
-internal-externc-isystem /usr/include -fdeprecated-macro
-fdebug-compilation-dir /Users/user/src/llvm-project -ferror-limit 19
-fmessage-length 80 -stack-protector 1 -fblocks
-fencode-extended-block-signature -fregister-global-dtors-with-atexit
-fobjc-runtime=macosx-10.14.0 -fcxx-exceptions -fexceptions
-fmax-type-align=16 -fdiagnostics-show-option -fcolor-diagnostics -o
test.o -x c++ /tmp/test.cpp
clang -cc1 version 10.0.0 based upon LLVM 10.0.0svn default target
x86_64-apple-darwin18.7.0
ignoring nonexistent directory
"/Users/user/src/clang-build-20190828/bin/../include/c++/v1"
ignoring nonexistent directory "/usr/include/c++/v1"
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /Users/user/src/clang-build-20190828/lib/clang/10.0.0/include
 /usr/include
 /System/Library/Frameworks (framework directory)
 /Library/Frameworks (framework directory)
End of search list.
/tmp/test.cpp:1:10: fatal error: 'string' file not found
#include <string>
         ^~~~~~~~
1 error generated.

 and with the Xcode clang:

clang++  -v -c /tmp/test.cpp
Apple clang version 11.0.0 (clang-1100.0.33.8)
Target: x86_64-apple-darwin18.7.0
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 x86_64-apple-macosx10.14.0 -Wdeprecated-objc-isa-usage
-Werror=deprecated-objc-isa-usage -emit-obj -mrelax-all -disable-free
-disable-llvm-verifier -discard-value-names -main-file-name test.cpp
-mrelocation-model pic -pic-level 2 -mthread-model posix
-mdisable-fp-elim -fno-strict-return -masm-verbose -munwind-tables
-target-cpu penryn -dwarf-column-info -debugger-tuning=lldb
-ggnu-pubnames -target-linker-version 512.4 -v -coverage-notes-file
/Users/jbj1/src/llvm-project/test.gcno -resource-dir
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/11.0.0
-stdlib=libc++ -internal-isystem
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1
-Wno-framework-include-private-from-public
-Wno-atimport-in-framework-header -Wno-extra-semi-stmt
-Wno-quoted-include-in-framework-header -fdeprecated-macro
-fdebug-compilation-dir /Users/jbj1/src/llvm-project -ferror-limit 19
-fmessage-length 80 -stack-protector 1 -mdarwin-stkchk-strong-link
-fblocks -fencode-extended-block-signature
-fregister-global-dtors-with-atexit -fobjc-runtime=macosx-10.14.0
-fcxx-exceptions -fexceptions -fmax-type-align=16
-fdiagnostics-show-option -fcolor-diagnostics -o test.o -x c++ /tmp/test.cpp
clang -cc1 version 11.0.0 (clang-1100.0.33.8) default target
x86_64-apple-darwin18.7.0
ignoring nonexistent directory "/usr/include/c++/v1"
#include "..." search starts here:
#include <...> search starts here:
 /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1
 /usr/local/include
 /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/clang/11.0.0/include
 /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include
 /usr/include
 /System/Library/Frameworks (framework directory)
 /Library/Frameworks (framework directory)
End of search list.


-- 
Jens B. Jorgensen
jbj1 at ultraemail.net