# Description

This folder contains configuration for [Nix](https://nixos.org/), a purely functional package manager used by the Status app for its build process.

## Configuration

The main config file is [`nix/nix.conf`](/nix/nix.conf) and its main purpose is defining the [binary caches](https://nixos.org/nix/manual/#ch-basic-package-mgmt) which allow download of packages to avoid having to compile them yourself locally.

__NOTE:__ If you are in Asia you might want to add the `https://nix-cache-cn.status.im/` to be first in order of `substituters`. Removing `cache.nixos.org` could also help.

## Build arguments

We leverage the standard nixpkgs `config` argument for our own parameterization of the builds (e.g. to pass a build number or build type). Here is a sample structure of the `config` attribute set:

```nix
config = {
  status-im = {
    ci = "1";                 # This flag is present when running in a CI environment
    build-type = "pr";        # Build type (influences which .env file gets used for feature flags)
    status-go = {
      src-override = "$GOPATH/src/github.com/status-im/status-go";
    };
    status-react = {
      build-number = "9999";  # Build number to be assigned to the app bundle
      gradle-opts = "";       # Gradle options passed for Android builds
    };
  };
};
```

## Shell

In order to access an interactive Nix shell a user should run `make shell`.

The Nix shell is started in this repo via the [`nix/scripts/shell.sh`](/nix/scripts/shell.sh) script, which is a wrapper around the `nix-shell` command and is intended for use with our main [`Makefile`](/Makefile). This allows for an implicit use of `nix-shell` as the default shell in the `Makefile`.

Normally the shell starts without any specific target platform, if you want to change that you should export the `TARGET` env variable with appropriate value:

```bash
make shell TARGET=android
```

This way your shell and all other nix commands should run in a setup that is tailored towards Android development.

For valid values you can check the [`nix/shells.nix`](/nix/shells.nix) file.

## Using a local status-go repository

If you need to use a locally checked-out status-go repository as a dependency of status-react, you can achieve that by defining the `STATUS_GO_SRC_OVERRIDE`
environment variable.

```sh
export STATUS_GO_SRC_OVERRIDE=$GOPATH/src/github.com/status-im/status-go
# Any command that you run from now on
# will use the specified status-go location
make release-android
```

or for a one-off build:

```sh
make release-android STATUS_GO_SRC_OVERRIDE=$GOPATH/src/github.com/status-im/status-go
```

## Known Issues

### MacOS 10.15 "Catalina"

There is an unsolved issue with the root(`/`) file system in `10.15` being read-only:
https://github.com/NixOS/nix/issues/2925

Our current recommended workaround is putting `/nix` under `/opt/nix` and symlinking it via `/etc/synthetic.conf`:

```bash
sudo mkdir /opt/nix
sudo chown ${USER} /opt/nix
sudo sh -c "echo 'nix\t/opt/nix' >> /etc/synthetic.conf"
reboot
```

After the system reboots you should see the `/nix` symlink in place:

```bash
 % ls -l /nix
lrwxr-xr-x  1 root  wheel  8 Oct 11 13:53 /nix -> /opt/nix
```

In order to be able to use Nix with a symlinked `/nix` you need to include this in your shell:

```bash
export NIX_IGNORE_SYMLINK_STORE=1
```

Add it to your `.bashrc` or any other shell config file.

__NOTE__: Your old `/nix` directory will end up in `/Users/Shared/Relocated Items/Security/nix` after OS upgrade.

### Cache Downloads Timing Out

If copying from Nix Cache times out you can adjust the timeout by changing [`nix/nix.conf`](/nix/nix.conf):
```conf
stalled-download-timeout = 9001
```