deduplication: Place link files under /gnu/store/.links.

Previously they'd always be placed next to TO-REPLACE, which would lead
to EPERM in some cases.

* guix/store/deduplication.scm (replace-with-link): Add #:swap-directory
parameter and honor it.  Add call to 'make-file-writable'.  Catch
'system-error' around 'rename-file'.
(deduplicate): Pass #:swap-directory and remove uses of
'false-if-system-error'.
* tests/store-deduplication.scm ("deduplicate"): Add 'chmod' call.

1 files changed, 4 insertions, 0 deletions

diff --git a/tests/store-deduplication.scm b/tests/store-deduplication.scm
index 23617231994..4ca2ec0f61e 100644
--- a/tests/store-deduplication.scm
+++ b/tests/store-deduplication.scm
@@ -47,6 +47,10 @@
                      (lambda (port)
                        (put-bytevector port data))))
                  identical)
+       ;; Make the parent of IDENTICAL read-only.  This should not prevent
+       ;; deduplication for inserting its hard link.
+       (chmod (dirname (second identical)) #o544)
+
        (call-with-output-file unique
          (lambda (port)
            (put-bytevector port (string->utf8 "This is unique."))))