In reply to @trofi:matrix.org

is there an easy way to make all local builds to check for reproducibility? (I'd like to check every package my system uses). I tried specifying --repeat 1 and did not notice any effect. Example command:

$ nix-build -E 'with import <nixpkgs> {}; builtins.derivation { name = "flaky-foo"; builder = "${bash}/bin/bash"; args = [ "-c" "${coreutils}/bin/date +%N > $out" ]; system = builtins.currentSystem; }' --repeat 10

I was just wondering if there's a good way to actually get an accurate SOURCE_DATE_EPOCH?

I've seen chroma uses leaveDotGit and grabs details and then deletes it to avoid issues: https://github.com/NixOS/nixpkgs/blob/nixos-unstable/pkgs/tools/text/chroma/default.nix#L17-L29

e.g. for SOURCE_DATE_EPOCH I'd swap the git command to $(git log -1 --pretty=%ct) etc https://reproducible-builds.org/docs/source-date-epoch/

I've not seen anyone propose SOURCE_DATE_EPOCH as a replacement for 1970-01-01-ing all files in nix.....

It's just that when developers want to expose a date in their version command there are a couple options: Leave it to some default like unknown, force it to the start of unix time, or use a reproducible date that's relevant to when the source code last changed which is where SOURCE_DATE_EPOCH came from

With a growing interest in reproducability projects such as ossf/scorecard are moving their scorecard version output from BuildDate: 2012-whatever-whatever to BuildDate: 1633648561
Since it's a reproducible date I don't see any reason to not fill it out beyond not being bothered