grafts: Rename files whose name matches a graft.

Fixes <http://bugs.gnu.org/23132>.
Reported by Mark H Weaver <mhw@netris.org>.

* guix/build/graft.scm (rename-matching-files): New procedure.
(rewrite-directory): Use it.
* tests/grafts.scm ("graft-derivation, renaming"): New test.

guix/build/graft.scm

@@ -83,6 +83,28 @@ writing the result to OUTPUT."
                           (put-u8 output (char->integer char))
                           result)))))
 
+(define (rename-matching-files directory mapping)
+  "Apply MAPPING to the names of all the files in DIRECTORY, where MAPPING is
+a list of store file name pairs."
+  (let* ((mapping (map (match-lambda
+                        ((source . target)
+                         (cons (basename source) (basename target))))
+                       mapping))
+         (matches (find-files directory
+                              (lambda (file stat)
+                                (assoc-ref mapping (basename file)))
+                              #:directories? #t)))
+
+    ;; XXX: This is not quite correct: if MAPPING contains "foo", and
+    ;; DIRECTORY contains "bar/foo/foo", we first rename "bar/foo" and then
+    ;; "bar/foo/foo" no longer exists so we fail.  Oh well, surely that's good
+    ;; enough!
+    (for-each (lambda (file)
+                (let ((target (assoc-ref mapping (basename file))))
+                  (rename-file file
+                               (string-append (dirname file) "/" target))))
+              matches)))
+
 (define* (rewrite-directory directory output mapping
                             #:optional (store (%store-directory)))
   "Copy DIRECTORY to OUTPUT, replacing strings according to MAPPING, a list of
@@ -127,6 +149,7 @@ file name pairs."
 
   (n-par-for-each (parallel-job-count)
                   rewrite-leaf (find-files directory (const #t)
-                                           #:directories? #t)))
+                                           #:directories? #t))
+  (rename-matching-files output mapping))
 
 ;;; graft.scm ends here

tests/grafts.scm

@@ -182,4 +182,21 @@
            (and (string=? (readlink one) repl)
                 (string=? (readlink two) one))))))
 
+(test-assert "graft-derivation, renaming"         ;<http://bugs.gnu.org/23132>
+  (let* ((build `(begin
+                   (use-modules (guix build utils))
+                   (mkdir-p (string-append (assoc-ref %outputs "out") "/"
+                                           (assoc-ref %build-inputs "in")))))
+         (orig  (build-expression->derivation %store "thing-to-graft" build
+                                              #:modules '((guix build utils))
+                                              #:inputs `(("in" ,%bash))))
+         (repl  (add-text-to-store %store "bash" "fake bash"))
+         (grafted (graft-derivation %store orig
+                                    (list (graft
+                                            (origin %bash)
+                                            (replacement repl))))))
+    (and (build-derivations %store (list grafted))
+         (let ((out (derivation->output-path grafted)))
+           (file-is-directory? (string-append out "/" repl))))))
+
 (test-end)