This document describes the layout of our Nix setup.

There are four main folders in the nix directory:

• nix/scripts - Bash scripts for easier usage of Nix
• nix/pkgs - Packages we add to or modify in nixpkgs
• nix/deps - Project dependencies managed by Nix
• nix/lib - Our tools we merge into pkgs.lib
• nix/tools - Various tools used by our derivations and shells
• nix/status-go - Derivations for building status-go repo

There are a few main files that define the whole build environment:

• nix/nix.conf - Binary cache configuration
• nix/default.nix - Entry point for both shells and targets
• nix/shell.nix - Definition of the default Nix shell
• nix/shells.nix - Definitions of other Nix shells used in builds
• nix/targets.nix - Hierarchy of main build targets
• nix/pkgs.nix - Definition of a custom nixpkgs repo
• nix/config.nix - Default config values for instantiating nixpkgs
• nix/overlay.nix - Overrides for nixpkgs, custom packages

The default.nix and shell.nix files at th repo root are just a gateway into the nix sub folder.

There's a few scripts in nix/scripts that make use of Nix simpler:

• nix/scripts/setup.sh - Installs Nix Package manager
• nix/scripts/source.sh - Sources the Nix profile or installs Nix
• nix/scripts/build.sh - A wrapper around nix-build with sane defaults
• nix/scripts/shell.sh - A wrapper around nix-shell for Makefile
• nix/scripts/clean.sh - For cleaning Nix store after builds
• nix/scripts/purge.sh - For purging everything Nix related from system

The starting point for using our Nix shells and targets is the default.nix file.

It pulls in all the pkgs, targets and shells defined in nix/default.nix. The point is easy access to them via commands like nix-build or nix-shell, which you'll see next.

Normally shells are started using make shell TARGET=android, but that is essentially the same as calling:

nix-shell -A shells.android default.nix

The nix/scripts/shell.sh script is essentially a wrapper around that command to make it usable as shell for the Makefile.

We will use the make jsbundle-android target as an example of a derivation you can build using Nix:

1. make jsbundle-android is called by developer
2. make calls nix/scripts/build.sh targets.mobile.android.jsbundle
3. build.sh calls nix-build --attr targets.mobile.android.jsbundle with extra arguments
4. nix-build builds the derivation from nix/mobile/android/jsbundle/default.nix

The same can be done for other targets like targets.mobile.android.release. Except in that case extra arguments are required which is why the scripts/release-android.sh is used in the make release-android target.

If you run make release-android you'll see the nix-build command used:

nix-build \
  --pure \
  --fallback \
  --no-out-link \
  --show-trace \
  --attr targets.mobile.android.release \
  --argstr secrets-file '/tmp/tmp-status-react-559a3a441/tmp.xAnrPuNtAP' \
  --option extra-sandbox-paths '/home/joe/.gradle/status-im.keystore /tmp/tmp-status-react-559a3a441/tmp.xAnrPuNtAP' \
  --arg config '{ \
    status-im.build-type="nightly";
    status-im.build-number="2020022418";
    status-im.android.keystore-path="/home/joe/.gradle/status-im.keystore";
    status-im.android.abi-split="false";
    status-im.android.abi-include="armeabi-v7a;arm64-v8a;x86";
  }' \
  default.nix

Some of those are required which is why just calling:

nix-build --attr targets.mobile.android.release

Would fail.

The make nix-gc target calls nix-store --gc and normally would remove almost everything, but to prevent that we place symlinks to protected derivations in /nix/var/nix/gcroots subfolder. Specifically:

_NIX_GCROOTS="${_NIX_GCROOTS:-/nix/var/nix/gcroots/per-user/${USER}/status-react}"

Whenever nix/scripts/build.sh or nix/scripts/shell.sh are called they update symlinks named after given targets in that folder. This in combination with keep-outputs = true set in nix/nix.conf prevents garbage collection from removing too much.