inferior: 'cached-channel-instance' takes an open store connection.

* guix/inferior.scm (cached-channel-instance): Take an explicit 'store'
argument.
(inferior-for-channels): Wrap call to 'cached-channel-instance' in
'with-store'.
* guix/time-machine.scm (guix-time-machine): Wrap call to
'cached-channel-instance' in 'with-store'.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

guix/inferior.scm

@@ -636,15 +636,14 @@ failing when GUIX is too old and lacks the 'guix repl' command."
   (make-parameter (string-append (cache-directory #:ensure? #f)
                                  "/inferiors")))
 
-(define* (cached-channel-instance channels
+(define* (cached-channel-instance store
+                                  channels
                                   #:key
                                   (cache-directory (%inferior-cache-directory))
                                   (ttl (* 3600 24 30)))
   "Return a directory containing a guix filetree defined by CHANNELS, a list of channels.
 The directory is a subdirectory of CACHE-DIRECTORY, where entries can be reclaimed after TTL seconds.
 This procedure opens a new connection to the build daemon."
-  (with-store store
-    (let ()
   (define instances
     (latest-channel-instances store channels))
 
@@ -687,7 +686,7 @@ This procedure opens a new connection to the build daemon."
             (built-derivations (list profile))
             (symlink* (derivation->output-path profile) cached)
             (add-indirect-root* cached)
-                (return cached))))))))
+            (return cached))))))
 
 (define* (inferior-for-channels channels
                                 #:key
@@ -700,7 +699,9 @@ procedure opens a new connection to the build daemon.
 This is a convenience procedure that people may use in manifests passed to
 'guix package -m', for instance."
   (define cached
-    (cached-channel-instance channels
+    (with-store store
+      (cached-channel-instance store
+                               channels
                                #:cache-directory cache-directory
-                             #:ttl ttl))
+                               #:ttl ttl)))
   (open-inferior cached))

guix/scripts/time-machine.scm

@@ -21,6 +21,7 @@
   #:use-module (guix scripts)
   #:use-module (guix inferior)
   #:use-module (guix channels)
+  #:use-module (guix store)
   #:use-module ((guix scripts pull) #:select (channel-list))
   #:use-module (ice-9 match)
   #:use-module (srfi srfi-1)
@@ -97,6 +98,7 @@ Execute COMMAND ARGS... in an older version of Guix.\n"))
            (channels     (channel-list opts))
            (command-line (assoc-ref opts 'exec)))
       (when command-line
-        (let* ((directory  (cached-channel-instance channels))
+        (let* ((directory  (with-store store
+                             (cached-channel-instance store channels)))
                (executable (string-append directory "/bin/guix")))
           (apply execl (cons* executable executable command-line)))))))