fix(nix-cache-server): patch nix-serve-ng for cppnix 2.30+ API drift

[Joaqim]

No description provided.

[Joaqim]

nix-cache-server now compiles against cppnix 2.30+. vira's transform pipeline patches nix-serve-ng-1.1.0 at build time, but three of the cbits/nix.cpp FFI bridges reference cppnix APIs that have since drifted. Without these sed substitutions, a fresh nix build against cppnix 2.30+ fails — most visibly with std::basic_string constructor ambiguity under gcc-15.

The three drifted call sites

Site	Symptom	Resolution
nix.cpp:153 settings.nixStore	Field removed from cppnix Settings singleton (globals.hh)	Use getStore()->storeDir from StoreDirConfig (store-dir-config.hh:33)
nix.cpp:209 std::vector<std::string> sigs(begin, end)	ValidPathInfo::sigs is now std::set<nix::Signature> (path-info.hh:105)	Project each element through nix::Signature::to_string()
nix.cpp:229,231 std::string = signDetached(...)	SecretKey::signDetached returns nix::Signature (local-keys.hh:78)	Append .to_string()

The patch

Three sed -i lines in packages/nix-cache-server/haskell-module.nix, alongside the existing #include rewrites:

${pkgs.gnused}/bin/sed -i 's|copyString(settings\.nixStore, output);|copyString(getStore()->storeDir, output);|' $out/cbits/nix.cpp
${pkgs.gnused}/bin/sed -i 's|std::vector<std::string> sigs(validPathInfo->sigs\.begin(), validPathInfo->sigs\.end());|std::vector<std::string> sigs; for (const auto \& s : validPathInfo->sigs) sigs.push_back(s.to_string());|' $out/cbits/nix.cpp
${pkgs.gnused}/bin/sed -i 's|signDetached(message);|signDetached(message).to_string();|' $out/cbits/nix.cpp

The third sed catches both pre- and post-Lix-2.94 branches since they share the trailing pattern.

Why this went undetected

.github/workflows/website.yaml builds only the docs site — CI never realises .#default or nix-cache-server. Runtime artefacts come prebuilt from cache.nixos.asia/oss declared in flake.nix:2-5, so fresh cppnix source rebuilds are never exercised. Upstream aristanetworks/nix-serve-ng has effectively become Lix-only — aristanetworks/nix-serve-ng#64 flagging cppnix 2.30+ incompatibility has been unanswered since 2026.

Consider adding a CI job that builds .#default (or just nix-cache-server) on Linux against cppnix in a fresh sandbox, so future API drift surfaces in CI rather than at deployment time on downstream forks.

Reproduction

nix build github:Joaqim/vira/cppnix-2.30-api-compat

Verified locally on cppnix 2.34.6: full build succeeds end-to-end, 3135-line build log shows zero error markers, produces vira-0.1.0.0 cleanly. Deployed and running as a systemd user service.

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Generated by Claude Code (model claude-opus-4-7). API-drift diagnosis, sed-patch design, and local build verification were AI-orchestrated; patches were reviewed against cppnix 2.34.6 headers before opening this draft.

[srid]

Thanks!

Upstream aristanetworks/nix-serve-ng has effectively become Lix-only — issue aristanetworks/nix-serve-ng#64 flagging cppnix 2.30+ incompatibility is unanswered since 2026-04-26.

Given this, I wonder if there's a alternative or fork that is official-Nix friendly?

[srid]

By the way, I offered to contribute to upstream (so as to obviate mainaining this patch here), but so far they have not responded to me: aristanetworks/nix-serve-ng#48

[Joaqim]

Yes, your opened issue surfaced during diagnosis, I choose to follow your established solution with just patching downstream instead.

[srid]

@Joaqim Did you run CI on this PR? Because it fails with: