> Everything is pinned to exact source revisions.

While you're here, how do you do this with nix-pkgs?

I looked into using nixos for nodejs deployments recently, and was amazed to find that the versions of node in the nix-pkgs repo are just pinned to X.Y.0 releases, with no discernable way to update to a bugfix release after .0 , so... I don't see how this could possibly be used for production deployments?

https://nixos.org/nixos/packages.html?channel=nixpkgs-unstab...

What I really want is to be able to tell nix to give me nodejs at version 10.16.3 and have it do the right thing every time.

I'm happy to be wrong on any of this.

While the nix package manager supports the coexistence of multiple versions of a package, the nixpkgs package collection does not contain every single versions of every package. However, it does make it very easy to refer to past versions of a package by importing package specifications from an older version of nixpkgs.

I think this is a reasonable choice, considering that the main purpose of nixpkgs is to provide packages for the NixOS distribution. It's impossible to actively maintain every single version of every package.

I think its a coincidence. Check nodejs commit history: https://github.com/NixOS/nixpkgs/commits/f3282c8d1e0ce6ba5d9... there are minor versions also

Right, so if I'm understanding correctly, I'd need to pin the whole nix-pkgs system to the particular git revision which contains the version I need?

That's it, also you can cherry pick different software from different git revisions.

Do you have any public examples of doing this? Or docs?

Closest I found was to pin the nix-channel entirely, but not different components to different versions.

You could do something like:

    let pinnedPkgs = import (builtins.fetchTarball {...}) {};
        node = pinnedPkgs.nodejs-10_x;

to refer to a specific version of node.

https://nixos.wiki/wiki/FAQ/Pinning_Nixpkgs

Thanks that helps.

I've mostly stuck to nix-shell -p foo bar baz to setup my environments. It's holding me back and I should pull the trigger on a shell.nix file, just gotta learn the language.

Agreed. Super painful to learn and still learning, but once it clicks, it's totally worth it. Amazing tool.

Occasionally I still run into weird non-deterministic issues with builds, though: https://github.com/NixOS/nixpkgs/issues/71178

You'd think "pinning" a python version + channel would avoid this.

How do you specify Python dependencies and their versions in Nix?

A quick and dirty way would be:

$ nix run "(import <nixpkgs> {}).python37.withPackages([ pandas statsmodels ])"

This would drop you into a shell with Python 3.7, pandas, and statsmodels installed.

For more complex use cases, you should specify your dependencies in a shell.nix file or write your own nix package.

And then to expand, if you wish to pin one of those packages to a specific rev, the easiest way is to create an "overlay" (it's a Nix design pattern) that you apply to nixpkgs to override whatever version is in your nixpkgs version.

Ditto, roughly.