| 25 Nov 2025 |
 megmug | It's interesting though that it already works on linux | 10:57:26 |
| megmug | Also, it didn't fail immediately - the same module using stdio.h + printf works on macos | 10:58:55 |
 Randy Eckenrode | C++ modules support is fixed on staging. | 11:32:05 |
| Randy Eckenrode | https://github.com/NixOS/nixpkgs/pull/462747 | 11:32:44 |
| Randy Eckenrode | A change was made to fix clang foo.cpp that broke clang-scan-deps, which CMake uses for module support. | 11:33:50 |
| Randy Eckenrode | It had to be ported to the clang-tools wrapper, which would have gone to master if not for the large number of Linux rebuilds it caused. | 11:34:43 |
| megmug | Aha - could this possibly affect non-module projects as well then? Because I am still getting errors despite removing all the modules. clang-scan-deps fails to find some stuff (on macos). | 11:37:28 |
| Randy Eckenrode | If it uses clang-scan-deps, it will be broken. | 11:39:02 |
| Randy Eckenrode | Also clangd. | 11:39:10 |
| Randy Eckenrode | You may be able to work around it by setting env.NIX_CFLAGS_COMPILE to -isystem ${stdenv.cc.libcxx}. | 11:42:42 |
| Randy Eckenrode | * You may be able to work around it by setting env.NIX_CFLAGS_COMPILE to -isystem ${stdenv.cc.libcxx}/include/c++/v1. | 11:43:01 |
| Randy Eckenrode | (Path from memory, so may be off.) | 11:43:14 |
| megmug | Hm, or just build the nix-shell on a different version maybe? Is the change already on master branch? Or can i go back far enough to get a version that didn't have the problem? | 11:44:38 |
| Randy Eckenrode | It’s on staging. It won’t make it to master until mid-December probably. | 11:47:04 |
| Randy Eckenrode | If you use staging, you’ll have to do a stdenv bootstrap and build everything from source. | 11:47:43 |
| megmug | Do I understand correctly that the breaking change was merged on oct 9? Could it be circumvented by going back further than that? | 11:52:20 |
| megmug | On the other hand, building everything from source might not be that bad as long as it's automatic | 11:53:09 |
| Randy Eckenrode | That should also work. | 11:56:55 |
| Randy Eckenrode | It is. It just takes a while. | 11:57:18 |
| megmug | After waiting for hours to let the machine build the staging commit, i had to discover that my issue persisted. After getting a message from a teammate that the project didn't build for him on an ubuntu Windows-WSL VM, i got suspicious. I thought i had double-checked with nix-shell --pure that it would build on other machines. And i was even using ubuntu for the test. It turns out we were missing a dependency. After adding pkgs.clang-tools into the nix-shell packages, the issue was resolved for the teammate and also on the Mac! I learned that it can be really difficult to make things work across different OSes and architectures. Without Nix it would without a doubt be a lot more difficult, though. | 22:41:44 |
