bug#52054: clangd cannot find <stddef.h>

[Ludovic Courtès]

Hello,

‘clangd’ fails to find <stddef.h>, as shown here:

--8<---------------cut here---------------start------------->8---
$ printf '#include <stdlib.h>\nint foo (int x) {return x+2; }' > t.c
$ guix shell -C -D hello --with-c-toolchain=hello=clang-toolchain clang:extra 
strace
guix shell: warning: transformation 'with-c-toolchain' had no effect on 
strace@5.8
guix shell: warning: transformation 'with-c-toolchain' had no effect on 
clang@12.0.1
[env]$ clang -c t.c
[env]$ clangd --check=t.c
I[10:02:40.349] clangd version 12.0.1
I[10:02:40.349] PID: 3
I[10:02:40.349] Working directory: /home/ludo/tmp/clangd-bug
I[10:02:40.349] argv[0]: clangd
I[10:02:40.349] argv[1]: --check=t.c
I[10:02:40.349] Entering check mode (no LSP server)
I[10:02:40.349] Testing on source file /home/ludo/tmp/clangd-bug/t.c
I[10:02:40.349] Loading compilation database...
I[10:02:40.349] Failed to find compilation database for 
/home/ludo/tmp/clangd-bug/t.c
I[10:02:40.349] Generic fallback command is: 
/gnu/store/nk5lp7wisgdlvds5camvcchgh19hnn23-clang-12.0.1/bin/clang 
/home/ludo/tmp/clangd-bug/t.c -fsyntax-only 
-resource-dir=/gnu/store/hnw2acjhfpj5l2zrazj5fvq5ksy002f1-clang-12.0.1-extra/lib/clang/12.0.1
I[10:02:40.350] Parsing command...
I[10:02:40.352] internal (cc1) args are: -cc1 -triple x86_64-unknown-linux-gnu 
-fsyntax-only -disable-free -disable-llvm-verifier -discard-value-names 
-main-file-name t.c -mrelocation-model static -mframe-pointer=all -fmath-errno 
-fno-rounding-math -mconstructor-aliases -munwind-tables -target-cpu x86-64 
-tune-cpu generic -fno-split-dwarf-inlining -debugger-tuning=gdb -resource-dir 
/gnu/store/hnw2acjhfpj5l2zrazj5fvq5ksy002f1-clang-12.0.1-extra/lib/clang/12.0.1 
-c-isystem /gnu/store/xl7wammzljnp0rg496n96h5m69y25isg-profile/include 
-cxx-isystem /gnu/store/xl7wammzljnp0rg496n96h5m69y25isg-profile/include 
-internal-isystem /usr/local/include -internal-isystem 
/gnu/store/hnw2acjhfpj5l2zrazj5fvq5ksy002f1-clang-12.0.1-extra/lib/clang/12.0.1/include
 -internal-externc-isystem 
/gnu/store/fa6wj5bxkj5ll1d7292a70knmyl7a0cr-glibc-2.31/include 
-fdebug-compilation-dir /home/ludo/tmp/clangd-bug -ferror-limit 19 
-fgnuc-version=4.2.1 -faddrsig -x c /home/ludo/tmp/clangd-bug/t.c
I[10:02:40.352] Building preamble...
I[10:02:40.368] Indexing headers...
E[10:02:40.382] [pp_file_not_found] Line 1: in included file: 'stddef.h' file 
not found
I[10:02:40.382] Building AST...
I[10:02:40.386] Indexing AST...
I[10:02:40.386] Testing features at each token (may be slow in large files)
I[10:02:40.387] All checks completed, 1 errors
[env]$ ls 
/gnu/store/hnw2acjhfpj5l2zrazj5fvq5ksy002f1-clang-12.0.1-extra/lib/clang/12.0.1
ls: cannot access 
'/gnu/store/hnw2acjhfpj5l2zrazj5fvq5ksy002f1-clang-12.0.1-extra/lib/clang/12.0.1':
 No such file or directory
[env]$ readlink -f $(type -P clang)
/gnu/store/nk5lp7wisgdlvds5camvcchgh19hnn23-clang-12.0.1/bin/clang-12
[env]$ find -L /gnu/store/nk5lp7wisgdlvds5camvcchgh19hnn23-clang-12.0.1/ -name 
stddef.h
/gnu/store/nk5lp7wisgdlvds5camvcchgh19hnn23-clang-12.0.1/lib/clang/12.0.1/include/stddef.h
[env]$ exit
$ guix describe
Generacio 195   Nov 22 2021 00:37:58    (nuna)
  guix 24aa7b3
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: 24aa7b3c21309b63cc6e8e18d6417d2cddccf6c6
--8<---------------cut here---------------end--------------->8---

Above, the directory passed as ‘-resource-dir’ does not exist: instead
of ‘…-clang-12.0.1-extra’ it should be ‘…-clang-12.0.1’.

This directory name is determined in ‘clangd/CompileCommands.cpp’:

--8<---------------cut here---------------start------------->8---
std::string detectStandardResourceDir() {
  static int Dummy; // Just an address in this process.
  return CompilerInvocation::GetResourcesPath("clangd", (void *)&Dummy);
}

[…]

CommandMangler CommandMangler::detect() {
  CommandMangler Result;
  Result.ClangPath = detectClangPath();
  Result.ResourceDir = detectStandardResourceDir();
  Result.Sysroot = detectSysroot();
  return Result;
}

[…]

  if (ResourceDir && !Has("-resource-dir"))
    Cmd.push_back(("-resource-dir=" + *ResourceDir));
--8<---------------cut here---------------end--------------->8---

We should either fix ‘GetResourcesPath’ or patch the file above so it
returns the Clang directory name known at build time.

Ludo’.