Make sure to deal with a repository

When checking when a repository is known or not be sure that there is
actually a chance that we are looking at a repository. If the thing to
be checked is neither a `<repository>' instance nor a string it's sure
that it's also not a registered repository.

gitto/git.scm

@@ -36,6 +36,7 @@
             repo-clean?
             repo-location
             repo-name
+            repository?
             same-repository?))
 
 (define show-unchanged-branches? #f)
@@ -55,6 +56,9 @@
   (clean? #:getter repo-clean?)
   (branches #:getter repo-branches))
 
+(define (repository? repo)
+  (is-a? repo <repository>))
+
 (define-method (branch-pullable (branch <branch>))
   (force (slot-ref branch 'pullable)))
 
@@ -180,6 +184,9 @@ REPO should be of type `<repository>' and the result is a string."
 (define-method (same-repository? (x <string>) (y <repository>))
   (string= x (repo-location y)))
 
+(define-method (same-repository? x y)
+  #f)
+
 (define* (start-git dir args #:optional (extra ""))
   (open-input-pipe
    (format #f "git --work-tree=~s --git-dir=\"~a/.git\" ~a 2>/dev/null ~a"

gitto/main.scm

@@ -100,9 +100,12 @@ COMMAND."
 
 (define (known? repo)
   "Do we know REPO?"
-  (or (member repo repositories same-repository?)
-      (member (realpath (if (string? repo) repo (repo-location repo)))
-              repositories same-repository?)))
+  (and (or (repository? repo) (string? repo))
+       (or (member repo repositories same-repository?)
+           (member (realpath (if (string? repo)
+                                 repo
+                                 (repo-location repo)))
+                   repositories same-repository?))))
 
 (define (save-repositories-list)
   "Save the list of repositories."