channels: Move ‘commit-short-id’ to (guix git).

* guix/channels.scm (commit-short-id): Move to…
* guix/git.scm (commit-short-id): … here.

Change-Id: If4b34b1d82b1aa5068d157f26e57e8aecc967061

guix/channels.scm

@@ -25,6 +25,7 @@
                            url+commit->name
                            commit-difference
                            repository-info
+                           commit-short-id
                            with-repository)
   #:autoload   (guix git-authenticate) (authenticate-repository)
   #:autoload   (guix openpgp) (openpgp-public-key-fingerprint
@@ -339,9 +340,6 @@ result is unspecified."
          (apply-patch patch checkout))
        (loop rest)))))
 
-(define commit-short-id
-  (compose (cut string-take <> 7) oid->string commit-id))
-
 (define* (authenticate-channel channel checkout commit
                                #:key (keyring-reference-prefix "origin/"))
   "Authenticate the given COMMIT of CHANNEL, available at CHECKOUT, a

guix/git.scm

@@ -67,6 +67,7 @@
             commit-relation
             commit-descendant?
             commit-id?
+            commit-short-id
 
             remote-refs
 
@@ -233,6 +234,9 @@ is a tag name.  This is based on a simple heuristic so use with care!"
   (and (= (string-length str) 40)
        (string-every char-set:hex-digit str)))
 
+(define commit-short-id
+  (compose (cut string-take <> 7) oid->string commit-id))
+
 (define (resolve-reference repository ref)
   "Resolve the branch, commit or tag specified by REF, and return the
 corresponding Git object."