Fix file-name-case-insensitive-p in ffap (bug#56443)

Don't crash if the file name argument to file-name-case-insensitive-p,
after expansion, doesn't have a parent directory.  This occurs
when calling ffap on something that looks like an email address.

* src/fileio.c (Ffile_name_case_insensitive_p): Return nil if no file
or parent directory could be found.
* test/src/fileio-tests.el (fileio-tests--identity-expand-handler)
(fileio--file-name-case-insensitive-p): New test.

1 files changed, 16 insertions, 0 deletions

diff --git a/test/src/fileio-tests.el b/test/src/fileio-tests.el
index c137ce06f1a..08582c8a862 100644
--- a/test/src/fileio-tests.el
+++ b/test/src/fileio-tests.el
@@ -201,4 +201,20 @@ Also check that an encoding error can appear in a symlink."
     (insert-file-contents "/dev/urandom" nil nil 10)
     (should (= (buffer-size) 10))))
 
+(defun fileio-tests--identity-expand-handler (_ file &rest _)
+  file)
+(put 'fileio-tests--identity-expand-handler 'operations '(expand-file-name))
+
+(ert-deftest fileio--file-name-case-insensitive-p ()
+  ;; Check that we at least don't crash if given nonexisting files
+  ;; without a directory (bug#56443).
+
+  ;; Use an identity file-name handler, as if called by `ffap'.
+  (let* ((file-name-handler-alist
+          '(("^mailto:" . fileio-tests--identity-expand-handler)))
+         (file "mailto:snowball@hell.com"))
+    ;; Check that `expand-file-name' is identity for this name.
+    (should (equal (expand-file-name file nil) file))
+    (file-name-case-insensitive-p file)))
+
 ;;; fileio-tests.el ends here