time-travel-manifest: Use a separate Git checkout cache.

* etc/time-travel-manifest.scm (guix-instance-compiler): Parameterize
%REPOSITORY-CACHE-DIRECTORY.

1 files changed, 13 insertions, 2 deletions

diff --git a/etc/time-travel-manifest.scm b/etc/time-travel-manifest.scm
index 3d7ecff370..f09659d20d 100644
--- a/etc/time-travel-manifest.scm
+++ b/etc/time-travel-manifest.scm
@@ -20,7 +20,11 @@
 ;;; releases from the current Guix, as per 'guix time-machine'.
 
 (use-modules (srfi srfi-9) (ice-9 match)
-             (guix channels) (guix gexp))
+             (guix channels) (guix gexp)
+             ((guix store) #:select (%store-monad))
+             ((guix monads) #:select (mparameterize return))
+             ((guix git) #:select (%repository-cache-directory))
+             ((guix build utils) #:select (mkdir-p)))
 
 ;; Representation of the latest channels.  This type exists just so we can
 ;; refer to such records in a gexp.
@@ -33,7 +37,14 @@
                                               system target)
   (match instance
     (($ <guix-instance> channels)
-     (latest-channel-derivation channels))))
+     ;; When this manifest is evaluated by Cuirass, make sure it does not
+     ;; fiddle with the cached checkout that Cuirass is also using since
+     ;; concurrent accesses are unsafe.
+     (mparameterize %store-monad ((%repository-cache-directory
+                                   (string-append (%repository-cache-directory)
+                                                  "/time-travel")))
+       (return (mkdir-p (%repository-cache-directory)))
+       (latest-channel-derivation channels)))))
 
 (define (guix-instance->manifest-entry instance)
   "Return a manifest entry for INSTANCE."