status-react/nix/DETAILS.md

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Description

This document describes the layout of our Nix setup.

Folders

There are four main folders in the nix directory:

Files

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

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

Scripts

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

Start

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.

Shells

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

nix-shell -A shells.default default.nix

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

Building

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

  1. make jsbundle is called by developer
  2. make calls nix/scripts/build.sh targets.mobile.jsbundle
  3. build.sh calls nix-build --attr targets.mobile.jsbundle with extra arguments
  4. nix-build builds the derivation from nix/mobile/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-mobile-559a3a441/tmp.xAnrPuNtAP' \
  --option extra-sandbox-paths '/home/joe/.gradle/status-im.keystore /tmp/tmp-status-mobile-559a3a441/tmp.xAnrPuNtAP' \
  default.nix

Some of those are required which is why just calling:

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

Would fail.

Garbage Collection

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-mobile}"

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.