Impure Build Due To validator_client/slashing_protection/Makefile

[patr-ck]

Description

The validator_client/slashing_protection/Makefile is curling a tarball during build. This impurity is making it impossible to write a nix expression to build lighthouse (which requires build purity).

Version

Stable Rust
Lighthouse v1.0.0

Present Behaviour

Not possible to write a nix expression for lighthouse.

Expected Behaviour

Possible to write a nix expression for lighthouse.

Steps to resolve

Remove the curl in the validator_client/slashing_protection/Makefile, and get that information is a pure way. For example, include the other repo as a submodule.

[michaelsproul]

I agree we need to remove that make and curl combo from the standard Lighthouse build as it's also holding up our Windows build too (#1237). That tarball is only required for testing, which is why I took the slightly hackier approach. I'm reluctant to just switch to a Git submodule, because we've found the UX of requiring users to clone with --recursive quite cumbersome. Instead I'm more inclined to move the make/curl/whatever to the test runner itself rather than the build script. That way you can compile Lighthouse without needing to download/have that tarball.

As a temporary work-around, could you include a Nix-native download step for that tarball in your Nix expression? It's pinned by git commit hash, so should have a consistent content hash for Nix to check. e.g.

b456887b2e4cb4a2dec22e7842ec10850ea8b99b78dcdbb3dcd20892e1aab266  interchange-tests-b8413ca42dc92308019d0d4db52c87e9e125c4e9.tar.gz

This is based on a brief dabble in Nix a few years ago, so apologies if that's not idiomatic. We'll fix it properly as well.