add a dummy artiq-timestamp.nix, generate through main.nix, use in artiq-manual.nix

artiq/default.nix

@@ -23,7 +23,7 @@ let
         };
       }) {} boards;
   manualPackages = import ./pkgs/artiq-manual.nix {
-    inherit stdenv lib fetchgit git python3Packages texlive texinfo;
+    inherit stdenv lib fetchgit python3Packages texlive texinfo;
     inherit (pythonDeps) sphinxcontrib-wavedrom;
   };
   mainPackages = rec {

artiq/pkgs/artiq-manual.nix

@@ -1,4 +1,4 @@
-{ stdenv, lib, fetchgit, git, python3Packages, texlive, texinfo, sphinxcontrib-wavedrom }:
+{ stdenv, lib, fetchgit, python3Packages, texlive, texinfo, sphinxcontrib-wavedrom }:
 
 let
   artiqVersion = import ./artiq-version.nix;
@@ -18,7 +18,6 @@ let
 
     src = import ./artiq-src.nix { inherit fetchgit; };
     buildInputs = [
-      git
       python3Packages.sphinx python3Packages.sphinx_rtd_theme
       python3Packages.sphinx-argparse sphinxcontrib-wavedrom
     ] ++
@@ -27,7 +26,7 @@ let
 
     preBuild = ''
         export VERSIONEER_OVERRIDE=${artiqVersion}
-        export SOURCE_DATE_EPOCH=`${git}/bin/git log -1 --format=%ct`
+        export SOURCE_DATE_EPOCH=${import ./artiq-timestamp.nix {}}
         cd doc/manual
       '';
     makeFlags = [ target ];

artiq/pkgs/artiq-timestamp.nix

@@ -0,0 +1,16 @@
+{ pkgs ? import <nixpkgs> {} }:
+with pkgs;
+let
+  artiq-timestamp = stdenv.mkDerivation {
+    name = "artiq-timestamp";
+    src = import ./artiq-src.nix { inherit fetchgit; };
+    buildInputs = [ git ];
+    buildPhase = ''
+      TIMESTAMP=`${git}/bin/git log -1 --format=%ct`
+    '';
+    installPhase = ''
+      echo \"$TIMESTAMP\" > $out
+    '';
+  };
+in
+  builtins.readFile artiq-timestamp

main.nix

@@ -5,6 +5,7 @@ let
     ''
     cp --no-preserve=mode,ownership -R ${./artiq} $out
     REV=`git --git-dir ${artiqSrc}/.git rev-parse HEAD`
+    TIMESTAMP=`git log -1 --format=%ct`
     ARTIQ_SRC_CLEAN=`mktemp -d`
     cp -a ${artiqSrc}/. $ARTIQ_SRC_CLEAN
     chmod -R 755 $ARTIQ_SRC_CLEAN/.git
@@ -20,6 +21,7 @@ let
     }
     EOF
     echo \"5e.`cut -c1-8 <<< $REV`\" > $out/pkgs/artiq-version.nix
+    echo \"$TIMESTAMP\" > $out/pkgs/artiq-timestamp.nix
     '';
   generateTestOkHash = pkgs.runCommand "generate-test-ok-hash" { buildInputs = [ pkgs.nix ]; }
     ''