emacs.pkgs.melpaBuild: package-build: 2018-10-05 -> 2021-04-13

I think this is due an update.  I've chosen to update to the latest
version that has been merged into Melpa.

Unfortunately we now need to hack around it trying to run VCS
commands.

My Emacs configuration with thirty-something leaf packages seems fine
after the rebuild.

pkgs/applications/editors/emacs/elisp-packages/libgenerated.nix

@@ -67,8 +67,7 @@ in {
         lib.nameValuePair ename (
           self.callPackage ({ melpaBuild, fetchurl, ... }@pkgargs:
           melpaBuild {
-            inherit pname;
-            ename = ename;
+            inherit pname ename commit;
             version = if isNull version then "" else
               lib.concatStringsSep "." (map toString version);
             # TODO: Broken should not result in src being null (hack to avoid eval errors)

pkgs/build-support/emacs/melpa.nix

@@ -38,8 +38,8 @@ import ./generic.nix { inherit lib stdenv emacs texinfo writeText; } ({
   packageBuild = fetchFromGitHub {
     owner = "melpa";
     repo = "package-build";
-    rev = "0a22c3fbbf661822ec1791739953b937a12fa623";
-    sha256 = "0dpy5p34il600sc8ic5jdgb3glya9si3lrvhxab0swks8fdydjgs";
+    rev = "047801d301a73d4932f33f768d94a8ed26b8d524";
+    sha256 = "0ygzkpg7xc3mjjbxg1kcyz6fwbkb0prvca499f0ffmhfaiv28h59";
   };
 
   elpa2nix = ./elpa2nix.el;
@@ -70,7 +70,7 @@ import ./generic.nix { inherit lib stdenv emacs texinfo writeText; } ({
         -L "$NIX_BUILD_TOP/package-build" \
         -l "$melpa2nix" \
         -f melpa2nix-build-package \
-        $ename $version
+        $ename $version $commit
 
     runHook postBuild
     '';

pkgs/build-support/emacs/melpa2nix.el

@@ -12,5 +12,8 @@
   (if (not noninteractive)
       (error "`melpa2nix-build-package' is to be used only with -batch"))
   (pcase command-line-args-left
-    (`(,package ,version)
+    (`(,package ,version ,commit)
+     ;; Monkey-patch package-build so it doesn't shell out to git/hg.
+     (defun package-build--get-commit (&rest _)
+       commit)
      (package-build--package (package-recipe-lookup package) version))))