There are a number of code samples throughout nix.dev. How do we know they still work? We don't! This commit introduces a way for us to extract these code samples into files and then run tests against them in CI. This will hopefully help us catch regressions in future updates to nix, NixOS and/or this guide. Additionally, I included a darwin specific nix-shell configuration that I use personally on my M1 Mac to work on this repo. Might be useful for someone.
2.5 KiB
Set up a development environment
Let's build a Python web application using the Flask web framework as an exercise.
Create a new file called default.nix
. This file is conventionally used for specifying packages. Add the code:
{ pkgs ? import <nixpkgs> {} }:
pkgs.python3Packages.buildPythonApplication {
pname = "myapp";
src = ./.;
version = "0.1";
propagatedBuildInputs = [ pkgs.python3Packages.flask ];
}
You will also need a simple Flask app as myapp.py
:
#! /usr/bin/env python
from flask import Flask
app = Flask(__name__)
@app.route("/")
def hello():
return "Hello, Nix!"
def run():
app.run(host="0.0.0.0")
if __name__ == "__main__":
run()
And a setup.py
script:
from setuptools import setup
setup(
name='myapp',
version='0.1',
py_modules=['myapp'],
entry_points={
'console_scripts': ['myapp = myapp:run']
},
)
Now build the package with:
nix-build
This will create a symbolic link result
to our package's path in the Nix store, which looks like /nix/store/6i4l781jwk5vbia8as32637207kgkllj-myapp-0.1
. Look around to see what's inside.
You may notice we can run the application from the package like this: ./result/bin/myapp.py
. But we can also use the default.nix
as a shell environment to get the same result:
nix-shell default.nix
python myapp.py
In this context, Nix takes on the role that you would otherwise use pip or virtualenv for. Nix installs required dependencies and separates the environment from others on your system.
You can check this Nix configuration into version control and share it with others to make sure you are all running the same software. This is a great way to prevent configuration drift between different team members & contributors, especially when a project has many dependencies.
You can also run a bash script like this one in your CI to make sure your default.nix
keeps working in the future.
#!/usr/bin/env nix-shell
#! nix-shell -i bash
set -euo pipefail
# start myapp in background and save the process id
python myapp.py >> /dev/null 2>&1 &
pid=$!
if [[ $(curl --retry 3 --retry-delay 1 --retry-connrefused http://127.0.0.1:5000) == "Hello, Nix!" ]]; then
echo "SUCCESS: myapp.py is serving the expected string"
kill $pid
exit 0
else
echo "FAIL: myapp.py is not serving the expected string"
kill $pid
exit 1
fi