fetchurl: output not reproducible

[davidak]

I have this data installed

[davidak@gaming:~]$ tree /nix/store/3xhqg2pw8xfvv1k1sbgagr97aasbab7g-Agave-Regular.ttf
/nix/store/3xhqg2pw8xfvv1k1sbgagr97aasbab7g-Agave-Regular.ttf
└── share
    └── fonts
        └── truetype
            └── Agave-Regular.ttf

now i change the fetchurl postFetch:

{ pkgs, lib, stdenv, fetchurl }:

stdenv.mkDerivation rec {
  pname = "agave";
  version = "16";

  src = fetchurl {
    url = "https://github.com/agarick/agave/releases/download/v${version}/Agave-Regular.ttf";
    downloadToTemp = true;
    recursiveHash = true;
    sha256 = "108jvcijnx06v1jzhnb28ql9nvmwqd83309834wcd4aii6bgf9ka";
    postFetch = ''
      install -D $downloadedFile $out/Agave-Regular.ttf
    '';
  };

  dontUnpack = true;
  dontConfigure = true;
  dontBuild = true;
  doCheck = false;
  dontFixup = true;
  #dontInstall = true;

  installPhase = ''
    runHook preInstall

    echo $src
    echo $out

    echo ------

    ls -la $src/share

    #install -D -t $out/ $src/*

    mkdir -p $out/share/fonts/truetype/
    cp $src/Agave-Regular.ttf $out/share/fonts/truetype/

    runHook postInstall
  '';



  meta = with lib; {
    description = "truetype monospaced typeface designed for X environments";
    homepage = "https://b.agaric.net/page/agave";
    license = licenses.mit;
    maintainers = with maintainers; [ dtzWill ];
    platforms = platforms.all;
  };
}

but the output of fetchurl has still the same hash and data is not changed... leading to 10 hours of debugging

...
building '/nix/store/y15ssw50vdb6wjcsags48zhmdy466yyd-agave-16.drv'...
patching sources
installing
/nix/store/3xhqg2pw8xfvv1k1sbgagr97aasbab7g-Agave-Regular.ttf
/nix/store/64c2gxl6fc3b1f46i60isvrdrx0pjp6s-agave-16
------
total 12
dr-xr-xr-x 3 nobody nogroup 4096 Jan  1  1970 .
dr-xr-xr-x 3 nobody nogroup 4096 Jan  1  1970 ..
dr-xr-xr-x 3 nobody nogroup 4096 Jan  1  1970 fonts
cp: cannot stat '/nix/store/3xhqg2pw8xfvv1k1sbgagr97aasbab7g-Agave-Regular.ttf/Agave-Regular.ttf': No such file or directory
builder for '/nix/store/y15ssw50vdb6wjcsags48zhmdy466yyd-agave-16.drv' failed with exit code 1
error: build of '/nix/store/y15ssw50vdb6wjcsags48zhmdy466yyd-agave-16.drv' failed

[Ma27]

When trying to build your code, I get the following error:

hash mismatch in fixed-output derivation '/nix/store/hakk1h2s2031njwn0zi6kxly7m4lbcw3-Agave-Regular.ttf':
  wanted: sha256-aib3lolRkcY4GSiBMVDDvG6bKEZiWfhl2AZ0KyPbEoE=
  got:    sha256-MTq4mBLSSKDNWV1XH6hBg+bvuYL+91jCx9T/CGcoJrU=
error: --- Error ------------------------------------------------------------------------ nix-build

I assume you didn't change the sha256 to a random value after modifying postFetch? If not (and a fixed-output path with the given sha256 exists in your store), nothing will be re-downloaded. See also NixOS/nix#969

[davidak]

@Ma27 yes, that's the reason. very annoying