nix build of the in-repo flake fails on release tags since v2.4.x (vergen NotPresent + missing libffi/libxml2 at link time)

[afool41]

Describe the bug

Title

nix build of the in-repo flake fails on release tags since v2.4.x (vergen NotPresent + missing libffi/libxml2 at link time)

Steps to reproduce

Description

The flake shipped in this repository no longer builds from a release tag tarball. Building v2.3.0 with Nix works, but v2.4.1 fails for two independent reasons. Both appear to be regressions introduced in the 2.4.x cycle and both only show up in environments without a .git directory and with a hermetic dependency set — i.e. exactly what nix build produces. main currently has the same flake.nix and build.rs, so this is still unfixed as of today.

Reproduction

nix build github:paradigmxyz/reth/v2.4.1#reth

(Also reproducible via a flake input pinned to the tag; same failures.)

Failure 1: vergen hard-fails without a git repository

crates/node/core/build.rs reads the git-derived variables with env::var(...)?:

let sha = env::var("VERGEN_GIT_SHA")?;

Nix fetches the tag as a tarball, so there is no .git. With the vergen version used up to v2.3.0, the emitter still populated the VERGEN_GIT_* variables with placeholder values when git information was unavailable, so the build script succeeded (with warnings). After the vergen bump in 2.4.x (BuildBuilder::default() → Build::builder() style API), the variables are simply not set when git is missing, and the build script aborts:

warning: reth-node-core@2.4.1: could not find repository at '.../crates/node/core'; class=Repository (6); code=NotFound (-3)
warning: reth-node-core@2.4.1: Unable to set VERGEN_GIT_DESCRIBE
warning: reth-node-core@2.4.1: Unable to set VERGEN_GIT_SHA
warning: reth-node-core@2.4.1: Unable to set VERGEN_GIT_DIRTY
error: failed to run custom build command for `reth-node-core v2.4.1`
...
--- stderr
Error: NotPresent

Workaround that confirms the diagnosis: setting VERGEN_DEFAULT_ON_ERROR=true (or pre-seeding VERGEN_GIT_SHA / VERGEN_GIT_DIRTY / VERGEN_GIT_DESCRIBE in the build environment) gets past this stage.

Suggested fix: make build.rs tolerate missing git info (fall back to defaults instead of ? on env::var), or set VERGEN_DEFAULT_ON_ERROR / provide the values inside the flake derivation. This would also fix any other from-tarball packaging (not just Nix).

Failure 2: link error — mold: fatal: library not found: ffi

With the vergen issue worked around, the build now compiles the entire workspace and fails at the final link of the reth binary:

error: linking with '.../clang' failed: exit status: 1
  = note: mold: fatal: library not found: ffi

The final link line contains -lffi and -lxml2, pulled in via the statically linked LLVM (llvm-sys / revmc-llvm, new in the 2.4.x dependency tree together with the withLlvm22 overlay added to flake.nix). The flake adds llvm.dev / llvm.lib to the build, but not libffi and libxml2, so in the hermetic Nix build sandbox the linker cannot find them.

Workaround that confirms the diagnosis: adding libffi and libxml2 to buildInputs of the reth derivation makes the build succeed:

buildInputs = old.buildInputs or [] ++ [ pkgs.libffi pkgs.libxml2 ];

Suggested fix: add pkgs.libffi and pkgs.libxml2 to buildInputs in the withLlvm22 override (or wherever the LLVM link deps are declared) in flake.nix.

Full workaround used locally

For reference, this overrideAttrs on packages.<system>.reth produces a working v2.4.1 build:

(reth.packages.${system}.reth).overrideAttrs (old: {
  # Failure 1
  VERGEN_GIT_SHA      = "8eb210175687c9f0c889a3b6795c16781d830e3a"; # commit of tag v2.4.1
  VERGEN_GIT_DIRTY    = "false";
  VERGEN_GIT_DESCRIBE = "v2.4.1";
  VERGEN_DEFAULT_ON_ERROR = "true";
  # Failure 2
  buildInputs = (old.buildInputs or []) ++ [ pkgs.libffi pkgs.libxml2 ];
})

Environment

• NixOS (nixos-unstable), x86_64-linux
• Building via the repo's own flake.nix at tag v2.4.1
• v2.3.0 builds fine from the same setup

Happy to open a PR for either fix if that helps.

Node logs

Platform(s)

Linux (x86)

Container Type

Not running in a container

What version/commit are you on?

v2.4.1 8eb2101

What database version are you on?

database version: 2

Which chain / network are you on?

ethereum mainnet

What type of node are you running?

Full via --full flag

What prune config do you use, if any?

No response

If you've built Reth from source, provide the full command you used

No response

Code of Conduct

• I agree to follow the Code of Conduct