melpaBuild: accept recipeFile in lieu of fileSpecs

pkgs/build-support/emacs/melpa.nix

@@ -8,6 +8,8 @@ with lib;
 { pname
 , version
 
+, recipeFile ? null
+
 , files ? null
 , fileSpecs ? [ "*.el" "*.el.in" "dir"
                 "*.info" "*.texi" "*.texinfo"
@@ -43,8 +45,17 @@ import ./generic.nix { inherit lib stdenv emacs texinfo; } ({
     runHook preBuild
 
     emacs --batch -Q -l $packageBuild -l ${./melpa2nix.el} \
+    ${if recipeFile == null
+      then
+      ''
       -f melpa2nix-build-package \
       ${pname} ${version} ${targets}
+      ''
+      else
+      ''
+      -f melpa2nix-build-package-from-recipe \
+      ${pname} ${version} ${recipeFile}
+      ''}
 
     runHook postBuild
   '';

pkgs/build-support/emacs/melpa2nix.el

@@ -21,6 +21,15 @@
     (`(,package ,version . ,files)
      (melpa2nix-package-build-archive package version files))))
 
+(defun melpa2nix-build-package-from-recipe ()
+  (if (not noninteractive)
+      (error "`melpa2nix-build-package' is to be used only with -batch"))
+  (pcase command-line-args-left
+    (`(,package ,version ,recipe-file)
+     (let* ((rcp (cdr (package-build--read-from-file recipe-file)))
+            (files (package-build--config-file-list rcp)))
+       (melpa2nix-package-build-archive package version files)))))
+
 (defun melpa2nix-package-build-archive (name version files)
   "Build a package archive for package NAME."
   (package-build--message "\n;;; %s\n" name)