clangd with compilation database and -stdlib=libc++

[Quuxplusone]

Bugzilla Link	PR43902
Status	NEW
Importance	P normal
Reported by	Fredrik Slättman (fredrik.slattman@gmail.com)
Reported on	2019-11-04 23:40:21 -0800
Last modified on	2019-11-04 23:42:25 -0800
Version	unspecified
Hardware	PC Linux
CC	llvm-bugs@lists.llvm.org
Fixed by commit(s)
Attachments	failing.log (4717 bytes, text/plain) working.log (3708 bytes, text/plain)
Blocks
Blocked by
See also

Created attachment 22768
Output from both NeoVim and clangd when it fails

When using clangd together with a compilation database which contains the
compiler flag -stdlib=libc++ clangd fails to find system headers.

I have created a git repo containing a reduced repro with logs that can be
 found here: https://github.com/fredrikslattman/clangd-libcpp.

Development Environment:
  Ubuntu 18.0.4 LTS
  LLVM/Clang-9 installed through apt-get
  CMake 3.15
  NeoVim 0.3.8 (with autozimu/LanguageClient 0.1.153)

clangd is being invoked with the --compile-commands-dir= which picks up the
correct compilation database.

[Quuxplusone]

Attached failing.log (4717 bytes, text/plain): Output from both NeoVim and clangd when it fails

[Quuxplusone]

Attached working.log (3708 bytes, text/plain): Logs from NeoVim and clangd when it works