cmake: Use -idirafter instead of -isystem #777
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isystem dirs are searched before the regular system dirs this exposes an interesting include ordering problem when using clang + libc++, when including C++ headers like <cstdlib> cstdlib includes stdlib.h and in case of libc++, this should be coming from libc++ as well, which is then eventually including system stdlib.h libc++ has added a check for checking this order recently, which means if cstlib ends up including system stdlib.h before libc++ provided stdlib.h it errors out | /mnt/b/yoe/master/build/tmp/work/riscv64-yoe-linux/libcereal/1.3.2+gitAUTOINC+ebef1e9298-r0/recipe-sysroot/usr/include/c++/v1/cwchar:113:5: error: <cwchar> tried including <wchar.h> but didn't find libc++'s <wcha r.h> header. This usually means that your header search paths are not configured properly. The header search paths should contain the C++ Standard Library headers before any C Standard Library, and you are probably using compiler flags that make that not be the case. | # error <cwchar> tried including <wchar.h> but didn't find libc++'s <wchar.h> header. \ | ^ The reason is that include_directories with SYSTEM property adds the directory via -system and some of these directories point to sysroot e.g. OPENSSL_INCLUDE_DIR which ends up adding -isystem <sysroot>/usr/include and causes the system stdlib.h to included before libc++ stdlib.h A fix is to use -idirafter which preserved the effects of system headers but instead of prepending, it will append to system headers and the issue is addressed Signed-off-by: Khem Raj <raj.khem@gmail.com>
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isystem dirs are searched before the regular system dirs this exposes an interesting include ordering problem when using clang + libc++, when including C++ headers like
cstdlib includes stdlib.h and in case of libc++, this should be coming from libc++ as well, which is then eventually including system stdlib.h
libc++ has added a check for checking this order recently, which means if cstlib ends up including system stdlib.h before libc++ provided stdlib.h it errors out
| /mnt/b/yoe/master/build/tmp/work/riscv64-yoe-linux/libcereal/1.3.2+gitAUTOINC+ebef1e9298-r0/recipe-sysroot/usr/include/c++/v1/cwchar:113:5: error: tried including <wchar.h> but didn't find libc++'s header. This usually means that your header search paths are not configured properly. The header search paths should contain the C++ Standard Library headers before any C Standard
Library, and you are probably using compiler flags that make that not be the case. | # error tried including <wchar.h> but didn't find libc++'s <wchar.h> header.
| ^
The reason is that include_directories with SYSTEM property adds the directory via -system and some of these directories point to sysroot e.g. OPENSSL_INCLUDE_DIR which ends up adding -isystem /usr/include and causes the system stdlib.h to included before libc++ stdlib.h
A fix is to use -idirafter which preserved the effects of system headers but instead of prepending, it will append to system headers and the issue is addressed
Signed-off-by: Khem Raj raj.khem@gmail.com