clangd doesn't find hardware_destructive_interference_size

[tarun-t]

Here's a minimal example:

#include <new>
#include <iostream>
int main() {
	std::cout << std::hardware_destructive_interference_size << std::endl;
	return 0;
}

Here's the output of clangd --check=test.cpp

I[11:35:55.284] Ubuntu clangd version 18.1.3 (++20240322073153+ef6d1ec07c69-1~exp1~20240322193300.86)
I[11:35:55.284] Features: linux+grpc
I[11:35:55.284] PID: 7556
I[11:35:55.284] Working directory: /home/tarun/
I[11:35:55.284] argv[0]: clangd
I[11:35:55.284] argv[1]: --check=test.cpp
I[11:35:55.284] Entering check mode (no LSP server)
I[11:35:55.284] Testing on source file /home/tarun//test.cpp
I[11:35:55.284] Loading compilation database...
I[11:35:55.284] Failed to find compilation database for /home/tarun/test.cpp
I[11:35:55.284] Generic fallback command is: [/home/tarun/] /usr/lib/llvm-18/bin/clang++ --driver-mode=g++ -std=c++23 -resource-dir=/usr/lib/llvm-18/lib/clang/18 -- /home/tarun/test.cpp
I[11:35:55.284] Parsing command...
I[11:35:55.285] internal (cc1) args are: -cc1 -triple x86_64-pc-linux-gnu -fsyntax-only -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 -debugger-tuning=gdb -fdebug-compilation-dir=/home/tarun/ -fcoverage-compilation-dir=/home/tarun/ -resource-dir /usr/lib/llvm-18/lib/clang/18 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/13/../../../../include/c++/13 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/13/../../../../include/x86_64-linux-gnu/c++/13 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/13/../../../../include/c++/13/backward -internal-isystem /usr/lib/llvm-18/lib/clang/18/include -internal-isystem /usr/local/include -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/13/../../../../x86_64-linux-gnu/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -std=c++23 -fdeprecated-macro -ferror-limit 19 -fgnuc-version=4.2.1 -fno-implicit-modules -fskip-odr-check-in-gmf -fcxx-exceptions -fexceptions -no-round-trip-args -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -x c++ /home/tarun/test.cpp
I[11:35:55.285] Building preamble...
I[11:35:55.437] Built preamble of size 4703320 for file /home/tarun/test.cpp version null in 0.15 seconds
I[11:35:55.437] Indexing headers...
I[11:35:55.472] Building AST...
E[11:35:55.495] [no_member] Line 4: no member named 'hardware_destructive_interference_size' in namespace 'std'
I[11:35:55.495] Indexing AST...
I[11:35:55.495] Building inlay hints
I[11:35:55.495] Building semantic highlighting
I[11:35:55.495] Testing features at each token (may be slow in large files)
I[11:35:55.497] All checks completed, 1 errors

Thanks in advance!

[HighCommander4]

I believe this is a feature that requires compiler support, and clang does not support it, i.e this code will not compile with clang as the compiler.

Since clangd uses clang's parser, that means clangd does not support it either.

[tarun-t]

Have changed the compiler to g++, can confirm that it compiles but clangd tells me it can't find it in g++ as well.

I[13:35:45.789] Ubuntu clangd version 18.1.3 (++20240322073153+ef6d1ec07c69-1~exp1~20240322193300.86)
I[13:35:45.789] Features: linux+grpc
I[13:35:45.789] PID: 7064
I[13:35:45.789] Working directory: /home/tarun/
I[13:35:45.789] argv[0]: clangd
I[13:35:45.789] argv[1]: --check=test.cpp
I[13:35:45.789] Entering check mode (no LSP server)
I[13:35:45.789] Testing on source file /home/tarun/test.cpp
I[13:35:45.789] Loading compilation database...
I[13:35:45.789] Failed to find compilation database for /home/tarun/test.cpp
I[13:35:45.789] Generic fallback command is: [/home/tarun/] /usr/lib/llvm-18/bin/g++ --driver-mode=g++ -std=c++23 -resource-dir=/usr/lib/llvm-18/lib/clang/18 -- /home/tarun/test.cpp
I[13:35:45.789] Parsing command...
I[13:35:45.790] internal (cc1) args are: -cc1 -triple x86_64-pc-linux-gnu -fsyntax-only -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 -debugger-tuning=gdb -fdebug-compilation-dir=/home/tarun/ -fcoverage-compilation-dir=/home/tarun/SPSCQueue -resource-dir /usr/lib/llvm-18/lib/clang/18 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/13/../../../../include/c++/13 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/13/../../../../include/x86_64-linux-gnu/c++/13 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/13/../../../../include/c++/13/backward -internal-isystem /usr/lib/llvm-18/lib/clang/18/include -internal-isystem /usr/local/include -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/13/../../../../x86_64-linux-gnu/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -std=c++23 -fdeprecated-macro -ferror-limit 19 -fgnuc-version=4.2.1 -fno-implicit-modules -fskip-odr-check-in-gmf -fcxx-exceptions -fexceptions -no-round-trip-args -faddrsig -D__GCC_HAVE_DWARF2_CFI_ASM=1 -x c++ /home/tarun/test.cpp
I[13:35:45.790] Building preamble...
I[13:35:45.942] Built preamble of size 4703320 for file /home/tarun/test.cpp version null in 0.15 seconds
I[13:35:45.942] Indexing headers...
I[13:35:45.978] Building AST...
E[13:35:46.002] [no_member] Line 4: no member named 'hardware_destructive_interference_size' in namespace 'std'
I[13:35:46.002] Indexing AST...
I[13:35:46.002] Building inlay hints
I[13:35:46.002] Building semantic highlighting
I[13:35:46.002] Testing features at each token (may be slow in large files)
I[13:35:46.057] All checks completed, 1 errors

[HighCommander4]

To clarify, clangd is built on clang's parser and thus always uses clang's parser to parse your code, that's the only thing it can do.

Whether the compiler in the compile command is clang or gcc only makes a fairly minor difference (e.g. it can affect the which standard library headers are used by default).

So, there is no way to get clangd to accept this code without clang accepting it.

[HighCommander4]

@tarun-t just as a heads up, clang trunk added support for hardware_destructive_interference_size recently: llvm/llvm-project#89446

So this should start working with clang(d) 19

[tarun-t]

Thanks for the update @HighCommander4