fix(dirvish): guard nil file and reject path-traversal playlist names

cj/set-wallpaper passed `(dired-file-name-at-point)` straight to `expand-file-name`, so running it with no file at point raised a bare `wrong-type-argument` instead of a clear error. cj/dired-create-playlist-from-marked expanded the raw playlist name under `music-dir` without checking it, so a name like "../foo" or "/etc/foo" would write outside the music directory.

I added a nil-file guard to set-wallpaper and a `cj/--playlist-name-safe-p` check that rejects any name carrying a directory separator before the path is built. Both paths now fail cleanly with a user-error. Regression tests went into the existing wrapper and playlist test files.

2 files changed, 21 insertions, 0 deletions

diff --git a/tests/test-dirvish-config-playlist.el b/tests/test-dirvish-config-playlist.el
index 3876a177..d059a899 100644
--- a/tests/test-dirvish-config-playlist.el
+++ b/tests/test-dirvish-config-playlist.el
@@ -78,5 +78,20 @@ lowercase extension list."
   "Boundary: a name that's just `.m3u' becomes empty after stripping."
   (should (equal (cj/--playlist-sanitize-name ".m3u") "")))
 
+;;; cj/--playlist-name-safe-p
+
+(ert-deftest test-cj--playlist-name-safe-p-bare-name ()
+  "Normal: a bare filename is safe."
+  (should (cj/--playlist-name-safe-p "roadtrip")))
+
+(ert-deftest test-cj--playlist-name-safe-p-empty ()
+  "Boundary: an empty name is not safe."
+  (should-not (cj/--playlist-name-safe-p "")))
+
+(ert-deftest test-cj--playlist-name-safe-p-rejects-separators ()
+  "Error: any directory separator (relative, absolute, or nested) is rejected."
+  (dolist (bad '("../evil" "../../etc/cron" "/etc/passwd" "sub/dir/name"))
+    (should-not (cj/--playlist-name-safe-p bad))))
+
 (provide 'test-dirvish-config-playlist)
 ;;; test-dirvish-config-playlist.el ends here
diff --git a/tests/test-dirvish-config-wrappers.el b/tests/test-dirvish-config-wrappers.el
index 7072fcf7..bead4583 100644
--- a/tests/test-dirvish-config-wrappers.el
+++ b/tests/test-dirvish-config-wrappers.el
@@ -140,5 +140,11 @@ calls the wallpaper-setter binary."
     (should (member "/some/picture.jpg" call-process-args))
     (should (string-match-p "Wallpaper set" msg))))
 
+(ert-deftest test-dirvish-set-wallpaper-no-file-errors ()
+  "Error: with no file at point, set-wallpaper signals user-error rather
+than passing nil to expand-file-name."
+  (cl-letf (((symbol-function 'dired-file-name-at-point) (lambda () nil)))
+    (should-error (cj/set-wallpaper) :type 'user-error)))
+
 (provide 'test-dirvish-config-wrappers)
 ;;; test-dirvish-config-wrappers.el ends here