clang-tools: clangd broken after staging-next 2025-11-02 merge

[jchv]

Nixpkgs version

• Unstable (25.11)

Describe the bug

clangd no longer works correctly after the staging-next merge. Including any standard header, e.g. <iostream>, fails with an error like 'iostream' file not found (clang pp_file_not_found). This is another bug that cropped up during the staging-next merge at de21549 (#457894).

Steps to reproduce

It's a bit hard to reproduce this from scratch, so I've taken two steps:

• I made a simple demo that has a shell script that will rapidly reproduce the problem. Check the README.
• I made a NixOS test (nixosTests.clangd: init #463366) based on this that I will try to get merged as soon as it passes again.

But in short, the problem occurs with almost any clangd setup I can find: clangd is no longer able to find include files after the staging merge. This seems to also be the case for any version of clangd I could find.

Expected behaviour

clangd should work I hope :)

Screenshots

No response

Relevant log output

{"jsonrpc":"2.0","method":"textDocument/publishDiagnostics","params":{"diagnostics":[{"code":"pp_file_not_found","message":"'iostream' file not found","range":{"end":{"character":19,"line":0},"start":{"character":9,"line":0}},"severity":1,"source":"clang"},{"code":"undeclared_var_use","message":"Use of undeclared identifier 'std'","range":{"end":{"character":5,"line":2},"start":{"character":2,"line":2}},"severity":1,"source":"clang"},{"code":"undeclared_var_use","message":"Use of undeclared identifier 'std'","range":{"end":{"character":37,"line":2},"start":{"character":34,"line":2}},"severity":1,"source":"clang"}],"uri":".../main.cpp","version":0}}I[23:03:57.286] --> reply:textDocument/documentHighlight(1) 11 ms

Additional context

No response

System metadata

• system: "x86_64-linux"
• host os: Linux 6.17.7, NixOS, 25.11 (Xantusia), 25.11.20251116.50a96ed
• multi-user?: yes
• sandbox: yes
• version: nix-env (Nix) 2.31.2
• channels(root): "nixos"
• channels(john): ""
• nixpkgs: /nix/store/c9asdiqw1rf5qwdjz26f57hp68ppb8fc-source

Notify maintainers

@Patryk27

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[jchv]

This is fixed by #462747, which was already cherrypicked into staging-25.11, so this issue may already be solved and just needs to make its way through staging and into channels.

It's really unfortunate that I only ever figure out that someone else has beat me to the punch with a fix after doing all of the work that would have been needed in the first place. Oh well, it is what it is...

[HuaHuaY]

Thank you for saving lots of my time. I search many websites but can't let clangd work well, until I found this issue and tried to use stable clang-tools instead of the unstable one.

[sadan4]

just ran into this after banging my head against a wall for a while, thanks!

[viperML]

I'm a bit lost about how is #462747 going to land in nixos-{25.11,unstable}, it was merged to staging 3 weeks ago already...

[Patryk27]

Hmm, the fix is present in staging-next-25.11:

https://github.com/NixOS/nixpkgs/blob/staging-next-25.11/pkgs/development/compilers/llvm/common/clang-tools/wrapper

Not sure why it hasn't been yet merged to nixos-25.11 🤔

[jchv]

I don't think there is a formal schedule for the progression of staging. The only formal document about staging processes I know of is this old RFC:

https://github.com/NixOS/rfcs/blob/master/rfcs/0026-staging-workflow.md

...which does not define when things merge.

Unfortunately that means it may take a while.

I think this tool should be able to track the progress, but as of now it doesn't seem the change has made its way to normal staging-next.

[Mythicsoul]

I found a fix that works in the meantime.

[evysgarden]

an easy fix is to use clang-tools from 25.05 while this is not merged

[jchv]

According to the nixpkgs-tracker tool this has made its way through the channels now, so as soon as we have that confirmed this issue should be good to close.