Clang++ cannot compile a C++ program after do-release-upgrade to Jammy

[Jeffrey Walton]

Hi Everyone.

I was running Ubuntu 20.04/Focal x86_64, fully patched. g++ and clang++ were installed and worked as expected. I ran do-release-upgrade to move to Ubuntu 22.04/Jammy. After Jammy g++ works but clang++ does not.

I performed a 'apt-get remove --purge clang*' followed by 'apt-get install clang'. No joy.

I manually installed libc++-abi and then libclang-cpp-dev. Still no joy.

Something is sideways with Clang on Ubuntu 22.04/Jammy. And I'm out of guesses.

-----

Here is the compile error I can't seem to shake - missing C++ headers. It looks like libc++ is not wired up correctly or libstdc++ is not wired up correctly. In either case, clang++ cannot seem to find the standard C++ headers or library.

$ clang++ -c test.cpp
test.cpp:1:10: fatal error: 'iostream' file not found
#include <iostream>
         ^~~~~~~~
1 error generated.

$ cat test.cpp
#include <iostream>
#include <string>

int main(int argc, char* argv[])
{
  std::string x(argv[0] ? argv[0] : "");
  std::cout << x << std::endl;
  return 0;
}

-----

And something more verbose:

$ clang++ -v -c test.cpp
Ubuntu clang version 14.0.0-1ubuntu1
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/11
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/12
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/9
Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/12
Candidate multilib: .;@m64
Selected multilib: .;@m64
 (in-process)
 "/usr/lib/llvm-14/bin/clang" -cc1 -triple x86_64-pc-linux-gnu -emit-obj -mrelax-all --mrelax-relocations -disable-free -clear-ast-before-backend -disable-llvm-verifier -discard-value-names -main-file-name test.cpp -mrelocation-model pic -pic-level 2 -pic-is-pie -mframe-pointer=all -fmath-errno -ffp-contract=on -fno-rounding-math -mconstructor-aliases -funwind-tables=2 -target-cpu x86-64 -tune-cpu generic -mllvm -treat-scalable-fixed-error-as-warning -debugger-tuning=gdb -v -fcoverage-compilation-dir=/home/jwalton -resource-dir /usr/lib/llvm-14/lib/clang/14.0.0 -internal-isystem /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++ -internal-isystem /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/x86_64-linux-gnu -internal-isystem /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/backward -internal-isystem /usr/lib/llvm-14/lib/clang/14.0.0/include -internal-isystem /usr/local/include -internal-isystem /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../x86_64-linux-gnu/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -fdeprecated-macro -fdebug-compilation-dir=/home/jwalton -ferror-limit 19 -fgnuc-version=4.2.1 -fcxx-exceptions -fexceptions -fcolor-diagnostics -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -o test.o -x c++ test.cpp
clang -cc1 version 14.0.0 based upon LLVM 14.0.0 default target x86_64-pc-linux-gnu
ignoring nonexistent directory "/usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/x86_64-linux-gnu"
ignoring nonexistent directory "/usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++/backward"
ignoring nonexistent directory "/usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../x86_64-linux-gnu/include"
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/bin/../lib/gcc/x86_64-linux-gnu/12/../../../../include/c++
 /usr/lib/llvm-14/lib/clang/14.0.0/include
 /usr/local/include
 /usr/include/x86_64-linux-gnu
 /usr/include
End of search list.
test.cpp:1:10: fatal error: 'iostream' file not found
#include <iostream>
         ^~~~~~~~~~
1 error generated.

-----

$ command -v g++
/usr/bin/g++

$ command -v clang++
/usr/bin/clang++

$ g++ --version
g++ (Ubuntu 11.3.0-1ubuntu1~22.04) 11.3.0
Copyright (C) 2021 Free Software Foundation, Inc.

$ clang++ --version
Ubuntu clang version 14.0.0-1ubuntu1
Target: x86_64-pc-linux-gnu
Thread model: posix
InstalledDir: /usr/bin

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 22.04.1 LTS
Release: 22.04
Codename: jammy

$ apt-cache show clang
Package: clang
Architecture: amd64
Version: 1:14.0-55~exp2
Priority: optional
Section: universe/devel
Source: llvm-defaults (0.55~exp2)
Origin: Ubuntu
Maintainer: Ubuntu Developers <email address hidden>
Original-Maintainer: LLVM Packaging Team <email address hidden>
Bugs: https://bugs.launchpad.net/ubuntu/+filebug
Installed-Size: 25
Depends: clang-14 (>= 14~)
Breaks: clang-3.2, clang-3.3, clang-3.4 (<< 1:3.4.2-7~exp1), clang-3.5 (<< 1:3.5~+rc1-3~exp1)
Replaces: clang (<< 3.2-1~exp2), clang-3.2, clang-3.3, clang-3.4 (<< 1:3.4.2-7~exp1), clang-3.5 (<< 1:3.5~+rc1-3~exp1)
Filename: pool/universe/l/llvm-defaults/clang_14.0-55~exp2_amd64.deb
Size: 3558
MD5sum: 9012efb7d550940265a49a8b3b986b1d
SHA1: a27e72f7f3e0d3ba8a84cf9e5612849ef11a46d9
...

-----

Finally:

$ update-alternatives --list clang++
update-alternatives: error: no alternatives for clang++

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Nicolas Simon (nimon77)]

An hotfix that worked for me is to install libstdc++-12-dev

[Shuhao (shuhao)]

This is also affecting clang-tidy, so if you use g++ normally to do development and use clang-tidy to check, this is causing it to all fail.

[Shuhao (shuhao)]

Also interesting is that this definitely worked before. I can reproduce this problem on multiple up-to-date jammy machines. However, on my ubuntu:jammy container, it worked (although my image is cached from about 5months ago).

[Shuhao (shuhao)]

This seems related: https://askubuntu.com/questions/1441844/todays-ubuntu-22-04-updates-seem-to-break-clang-compiler.

Can confirm that installing g++-12 solves this issue.

[Kevin Lalumiere (klalumiere)]

I wrote a Stack Overflow answer on this issue: https://stackoverflow.com/a/74605488/3068259

[Jerome Droniou (jdroniou)]

I can also confirm that the problem occurs on Ubuntu 20.04 that was dist-upgraded to 22.04, but not on a clean install of 22.04. I have two machines, each with one of these installs, and on the one where 22.04 was installed from scratch my clang++ still works fine, but on the one that was upgraded 20.04->22.04, clang++ cannot find most of the standard header files (iostream, cassert, etc.).