git: 'commit-difference' really excludes the ancestors of #:excluded.

* guix/git.scm (commit-difference): Initialize VISITED to the closure of
OLD and EXCLUDED, as written in the docstring.
* tests/git.scm ("commit-difference, excluded commits"): Adjust
accordingly.

2 files changed, 4 insertions, 3 deletions

diff --git a/guix/git.scm b/guix/git.scm
index 1671f57d9f4..0d8e617cc9c 100644
--- a/guix/git.scm
+++ b/guix/git.scm
@@ -416,7 +416,9 @@ Essentially, this computes the set difference between the closure of NEW and
 that of OLD."
   (let loop ((commits (list new))
              (result '())
-             (visited (commit-closure old (list->setq excluded))))
+             (visited (fold commit-closure
+                            (setq)
+                            (cons old excluded))))
     (match commits
       (()
        (reverse result))
diff --git a/tests/git.scm b/tests/git.scm
index 4a806abcc30..aa4f03ca62c 100644
--- a/tests/git.scm
+++ b/tests/git.scm
@@ -119,8 +119,7 @@
                     (list commit3 commit4))
              (lset= eq? (commit-difference commit4 commit1 (list commit3))
                     (list commit4))
-             (lset= eq? (commit-difference commit4 commit1 (list commit5))
-                    (list commit2 commit3 commit4)))))))
+             (null? (commit-difference commit4 commit1 (list commit5))))))))
 
 (unless (which (git-command)) (test-skip 1))
 (test-equal "commit-relation"