How can I provide packages to tex via nix?

I'm using nix to set up a little environment I can use for latex. I want to compile a small standalone document with tikz drawing. So I have this minimal tex file:

\documentclass{standalone}
\usepackage{tikz}
\begin{document}
  \begin{tikzpicture}
    \draw(0,0)circle(8);
  \end{tikzpicture}
\end{document}

This should need the pgf package for tikz and the standalone package for standalone. So I have my nix.shell

{ pkgs ? import <nixpkgs> {} }:
  let
    tex =
      pkgs.texlive.combine
        { inherit (pkgs.texlive) scheme-minimal pgf standalone;
        };
  in
    pkgs.mkShell
      { nativeBuildInputs =
        [ tex
        ];
      }

If I run my shell and attempt to compile with pdflatex:

[nix-shell:~/Projects/Tex]$ pdflatex example.tex 
This is pdfTeX, Version 3.141592653-2.6-1.40.22 (TeX Live 2021/NixOS.org) (preloaded format=pdflatex)
 restricted \write18 enabled.
entering extended mode
(./example.tex
LaTeX2e <2021-11-15> patch level 1
L3 programming layer <2022-02-24>

! LaTeX Error: File `standalone.cls' not found.

It seems that latex is not aware of the packages, which isn't very surprising. But I don't really know how to do this. I've looked at texlive on the nixos wiki which doesn't say very much. They have an example which looks like what I have other than the fact it is using the home manager.

How do I make the packages installed via nix available for pdflatex?

Solution

I'm not sure why, but pdflatex is not available in scheme-minimal (even though pdftex is available). This can be verified with pure nix-shell:

$ nix-shell --pure                                                                                                                     

[nix-shell:~]$ pdflatex
The program 'pdflatex' is not in your PATH. It is provided by several packages.
You can make it available in an ephemeral shell by typing one of the following:
  nix-shell -p tetex
  nix-shell -p texlive.combined.scheme-basic
  nix-shell -p texlive.combined.scheme-full
  nix-shell -p texlive.combined.scheme-gust
  nix-shell -p texlive.combined.scheme-medium
  nix-shell -p texlive.combined.scheme-small
  nix-shell -p texlive.combined.scheme-tetex

What happens in your case is that you run pdflatex from your main system, which does not have standalone available. If you change scheme-minimal to scheme-small, pdflatex will be available in the shell and everything will work.