Walk up the directory tree

Question

The file tree is as follwing:

- foo
  - lorem
    - ipsum <-
  - baz <-
- bar
- baz

The currently visited file is ipsum. Now

Answer 1

(defun parent-directory (dir)
  (unless (equal "/" dir)
    (file-name-directory (directory-file-name dir))))

(defun find-file-in-heirarchy (current-dir fname)
  "Search for a file named FNAME upwards through the directory hierarchy, starting from CURRENT-DIR" 
  (let ((file (concat current-dir fname))
        (parent (parent-directory (expand-file-name current-dir))))
    (if (file-exists-p file)
        file
      (when parent
        (find-file-in-heirarchy parent fname)))))

If the result is not nil, you can extract the file's directory using file-name-directory, like so:

(let ((file (find-file-in-heirarchy (buffer-file-name) "baz")))
  (when file
    (file-name-directory file)))

Answer 2

You want locate-dominating-file.