Latex "\today" macro expands to December 31st, 1979

Guides
1

With latex installed through the nix package manager (on nixos), \today always expands to December 31st, 1979 instead of the current date. How can I get this to give return the correct date? Files corrected with nix build users have modification times of that date too so is this related?

MWE

Create a directory and add the mwe.tex and flake.nix (based off Exploring Nix Flakes: Build LaTeX Documents Reproducibly).

– mwe.tex –

\documentclass[11pt]{article}

\title{}
\date{\today}

\begin{document}
\maketitle
\end{document}

– mwe.tex ends here –

– flake.nix –

{
  description = "MWE for reproducing \\today macro problem";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs";
    flake-utils.url = "github:numtide/flake-utils";
  };

  outputs = { self, nixpkgs, flake-utils }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = nixpkgs.legacyPackages.${system};
        tex = pkgs.texlive.combine {
          inherit (pkgs.texlive) scheme-minimal latex-bin latexmk;
        };
      in rec {
        packages = {
          document = pkgs.stdenvNoCC.mkDerivation rec {
            name = "mwe";
            src = self;
            buildInputs = [ pkgs.coreutils tex ];
            phases = [ "unpackPhase" "buildPhase" "installPhase" ];
            buildPhase = ''
              export PATH="${pkgs.lib.makeBinPath buildInputs}";
              mkdir -p .cache/texmf-var
              env TEXMFHOME=.cache TEXMFVAR=.cache/texmf-var \
                latexmk -pdf -lualatex mwe.tex
            '';
            installPhase = ''
              mkdir -p $out
              cp mwe.pdf $out/
            '';
          };
        };
        defaultPackage = packages.document;
      });
}

– flake.nix ends here –

Then run nix build "." in the new directory. The results should be a pdf containing December 31, 1979 (or when I just ran this I actually got January 1, 1980). I get the same problem when running latexmk as myself at the command line so it’s not only when the file is compiled by a nix build user.j

3 Likes
2

I have latex install using home-manager (package texlive.combined.scheme-full). I tried your tex file and it’s not happening. The PDF contains December 16, 2021. I compiled using pdflatex.

1 Like
3

Tried it with pdflatex and xelatex and date is correct for both. Might be a problem with lualatex and not nix then.

1 Like
4

I read the article you linked, you have to export SOURCE_DATE_EPOCH:

# self.lastModified is the date of last commit
SOURCE_DATE_EPOCH=${toString self.lastModified}

or

# a date you want
SOURCE_DATE_EPOCH=$(date -d "2021-11-30" +%s)
2 Likes
5

That’s embarrassing. Thank you for pointing that out.

1 Like
6

But the problem still exists: Why doesn’t LuaLaTeX use the current (build) time by default when SOURCE_DATE_EPOCH is not set?

7

It totally should, but by default the build epoch is set by the stdenv

1 Like