[kdevelop] [Bug 360074] New: Include paths detected wrongly with clang and libc++

[John via KDE Bugzilla]

https://bugs.kde.org/show_bug.cgi?id=360074

Bug ID: 360074
Summary: Include paths detected wrongly with clang and libc++
Product: kdevelop
Version: 4.90.91
Platform: Archlinux Packages
OS: Linux
Status: UNCONFIRMED
Severity: normal
Priority: NOR
Component: Language Support: CPP (Clang-based)
Assignee: kdevelop-bugs-***@kde.org
Reporter: ***@gmail.com

When i use clang with libc++, KDevelop still uses the libstdc++ headers causing
all kinds of problems with library types that aren't yet included in libstdc++.

After an initial investigation i am guessing the include paths are discovered
from GccLikeCompiler::includes. Unfortunately using "clang++ -E -v" only shows
the default settings that clang was compiled with, which is the libstdc++
setup.

Using "clang++ -Wp,-v" however shows the include paths that are actually used.
The same options also work for g++ too. The only problem is that it then
expects an input file so i would suggest "clang++ -Wp,-v dummy.cpp
-fsyntax-only"

Reproducible: Always

[Milian Wolff via KDE Bugzilla]

https://bugs.kde.org/show_bug.cgi?id=360074

--- Comment #1 from Milian Wolff <***@milianw.de> ---
I think you just need to pass `-stdlib=libc++` to the compiler from the
compiler settings dialog. That should - hopefully - work.

I'll keep this bug open, as we should make it simpler to switch between the
libs, and potentially read that data from CMake directly, if possible.

[John via KDE Bugzilla]

https://bugs.kde.org/show_bug.cgi?id=360074

--- Comment #2 from John <***@gmail.com> ---
I am not using CMake.

I already am adding -stdlib=libc++ to the parser command line (Right click
project -> Open Configuration -> Language support -> C/C++ Parser and setting a
custom profile with -stdlib=libc++).

I think the problem is simply that clang returns the wrong details with -E -v.
Note the warning about not using the the stdlib argument.

[***@aglap ~]$ clang++ -E -v
clang version 3.7.1 (tags/RELEASE_371/final)
Target: x86_64-unknown-linux-gnu
Thread model: posix
Found candidate GCC installation:
/usr/bin/../lib/gcc/x86_64-unknown-linux-gnu/5.3.0
Found candidate GCC installation:
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.3.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-unknown-linux-gnu/5.3.0
Found candidate GCC installation: /usr/lib64/gcc/x86_64-unknown-linux-gnu/5.3.0
Selected GCC installation: /usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.3.0
Candidate multilib: .;@m64
Selected multilib: .;@m64

[***@aglap ~]$ clang++ -E -v -stdlib=libc++
clang version 3.7.1 (tags/RELEASE_371/final)
Target: x86_64-unknown-linux-gnu
Thread model: posix
Found candidate GCC installation:
/usr/bin/../lib/gcc/x86_64-unknown-linux-gnu/5.3.0
Found candidate GCC installation:
/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.3.0
Found candidate GCC installation: /usr/lib/gcc/x86_64-unknown-linux-gnu/5.3.0
Found candidate GCC installation: /usr/lib64/gcc/x86_64-unknown-linux-gnu/5.3.0
Selected GCC installation: /usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.3.0
Candidate multilib: .;@m64
Selected multilib: .;@m64
clang-3.7: warning: argument unused during compilation: '-stdlib=libc++'

[***@aglap ~]$ clang++ -Wp,-v dummy.cpp -fsyntax-only
clang -cc1 version 3.7.1 based upon LLVM 3.7.1 default target
x86_64-unknown-linux-gnu
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:

/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.3.0/../../../../include/c++/5.3.0

/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.3.0/../../../../include/c++/5.3.0/x86_64-unknown-linux-gnu

/usr/bin/../lib64/gcc/x86_64-unknown-linux-gnu/5.3.0/../../../../include/c++/5.3.0/backward
/usr/local/include
/usr/bin/../lib/clang/3.7.1/include
/usr/include
End of search list.

[***@aglap ~]$ clang++ -Wp,-v dummy.cpp -fsyntax-only -stdlib=libc++
clang -cc1 version 3.7.1 based upon LLVM 3.7.1 default target
x86_64-unknown-linux-gnu
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/bin/../include/c++/v1
/usr/local/include
/usr/bin/../lib/clang/3.7.1/include
/usr/include
End of search list.

[John via KDE Bugzilla]

https://bugs.kde.org/show_bug.cgi?id=360074

--- Comment #3 from John <***@gmail.com> ---
My apologies. It is still not working, although i may well be completely wrong
about the cause of the problem because if the detection is through
GccLikeCompiler::includes, then i don't think it would succeed at parsing any
of the -E -v output anyway because it doesn't match what the code is looking
for.

[Milian Wolff via KDE Bugzilla]

https://bugs.kde.org/show_bug.cgi?id=360074

--- Comment #4 from Milian Wolff <***@milianw.de> ---
Your command is wrong/incomplete:

clang++ -std=c++11 -xc++ -dM -E -v /dev/null

vs

clang++ -std=c++11 -stdlib=libc++ -xc++ -dM -E -v /dev/null

I get different output as expected.