package-build: don't use mtime when creating tarballs

pkgs/build-support/emacs/melpa.nix

@@ -35,13 +35,26 @@ import ./generic.nix { inherit lib stdenv emacs texinfo writeText gcc; } ({
     then pname
     else ename;
 
-  packageBuild = fetchFromGitHub {
+  packageBuild = stdenv.mkDerivation {
+    name = "package-build";
+    src = fetchFromGitHub {
       owner = "melpa";
       repo = "package-build";
       rev = "c3c535e93d9dc92acd21ebc4b15016b5c3b90e7d";
       sha256 = "17z0wbqdd6fspbj43yq8biff6wfggk74xgnaf1xx6ynsp1i74is5";
     };
 
+    patches = [ ./package-build-dont-use-mtime.patch ];
+
+    dontConfigure = true;
+    dontBuild = true;
+
+    installPhase = "
+      mkdir -p $out
+      cp -r * $out
+    ";
+  };
+
   elpa2nix = ./elpa2nix.el;
   melpa2nix = ./melpa2nix.el;
 

pkgs/build-support/emacs/package-build-dont-use-mtime.patch

@@ -0,0 +1,40 @@
+diff --git a/package-build.el b/package-build.el
+index e572045..9eb0f82 100644
+--- a/package-build.el
++++ b/package-build.el
+@@ -415,7 +415,7 @@ (defun package-build--write-pkg-file (desc dir)
+       (princ ";; Local Variables:\n;; no-byte-compile: t\n;; End:\n"
+              (current-buffer)))))
+ 
+-(defun package-build--create-tar (name version directory mtime)
++(defun package-build--create-tar (name version directory)
+   "Create a tar file containing the contents of VERSION of package NAME.
+ DIRECTORY is a temporary directory that contains the directory
+ that is put in the tarball.  MTIME is used as the modification
+@@ -434,7 +434,7 @@ (defun package-build--create-tar (name version directory mtime)
+        ;; prevent a reproducable tarball as described at
+        ;; https://reproducible-builds.org/docs/archives.
+        "--sort=name"
+-       (format "--mtime=@%d" mtime)
++       "--mtime=@0"
+        "--owner=0" "--group=0" "--numeric-owner"
+        "--pax-option=exthdr.name=%d/PaxHeaders/%f,delete=atime,delete=ctime"))
+     (when (and package-build-verbose noninteractive)
+@@ -848,12 +848,11 @@ (defun package-build--build-multi-file-package (rcp version commit files source-
+                            (package-build--desc-from-library
+                             name version commit files 'tar)
+                            (error "%s[-pkg].el matching package name is missing"
+-                                  name))))
+-               (mtime (package-build--get-commit-time rcp commit)))
++                                  name)))))
+           (package-build--copy-package-files files source-dir target)
+           (package-build--write-pkg-file desc target)
+           (package-build--generate-info-files files source-dir target)
+-          (package-build--create-tar name version tmp-dir mtime)
++          (package-build--create-tar name version tmp-dir)
+           (package-build--write-pkg-readme name files source-dir)
+           (package-build--write-archive-entry desc))
+       (delete-directory tmp-dir t nil))))
+-- 
+2.37.2
+