nonguix: Add package-input-grafting.

* nonguix/utils.scm (package-input-grafting): New procedure.

nonguix/utils.scm

@@ -11,7 +11,8 @@
   #:use-module (guix utils)
   #:use-module (guix packages)
   #:use-module (gnu services)
-  #:export (with-transformation))
+  #:export (package-input-grafting
+            with-transformation))
 
 (define-public (to32 package64)
   "Build package for i686-linux.
@@ -26,6 +27,34 @@ Only x86_64-linux and i686-linux are supported.
                     ,@(package-arguments package64)))))
     (_ package64)))
 
+(define (package-input-grafting replacements)
+  "Return a procedure that, when passed a package, grafts its direct and
+indirect dependencies, including implicit inputs, according to REPLACEMENTS.
+REPLACEMENTS is a list of package pairs; the first element of each pair is the
+package to replace, and the second one is the replacement.
+
+Name and version of replacement packages will be padded to meet graft
+requirement."
+  (package-input-rewriting
+   (map (match-lambda
+          ((old . new)
+           `(,old . ,(package
+                       (inherit old)
+                       (replacement
+                        (package
+                          (inherit new)
+                          (name
+                           (string-pad-right
+                            (package-name new)
+                            (string-length (package-name old))
+                            #\0))
+                          (version
+                           (string-pad-right
+                            (package-version new)
+                            (string-length (package-version old))
+                            #\0))))))))
+        replacements)))
+
 ;; For concerns and direction of improvement, see this thread:
 ;; https://lists.gnu.org/archive/html/guix-devel/2024-06/msg00275.html
 (define* (with-transformation proc obj #:optional (pred package?))