bug#19140: dir-locals-collect-variables discrepancy in handling non-file buffers

[Ivan Shmakov]

Package:  emacs
Severity: minor

        Please consider the patch MIMEd.

        * lisp/files.el (dir-locals-collect-variables): Use
        default-directory in place of the file name while working on
        non-file buffers (as hack-dir-local-variables already does.)

        The issue I observe is as follows.  First, I create ~/foo and
        ~/foo/ru directories, and a ~/foo/.dir-locals.el file like:

((nil
  (ispell-local-dictionary  . "esperanto"))
 ("ru"
  (nil
   (ispell-local-dictionary . "russian"))))

        Then:

(with-temp-buffer
  (cd "~/foo/ru/")
  (hack-dir-local-variables-non-file-buffer)
  ;; .
  dir-local-variables-alist)

        The result is '((ispell-local-dictionary . "esperanto")),
        contrary to the expected '((… . "russian")).

        This does not happen for buffers associated with files:

(with-current-buffer (find-file-noselect "~/foo/ru/bar")
  (hack-dir-local-variables)
  ;; .
  dir-local-variables-alist)

        Reading the code suggests that dir-locals-collect-variables
        fails to handle the (stringp key) case properly when ‘file-name’
        is nil, which is what my patch is intended to fix.

-- 
FSF associate member #7257  np. Conclusion — Apocalyptica    … B6A0 230E 334A

--- a/lisp/files.el
+++ b/lisp/files.el
@@ -3567,8 +3569,10 @@
 (defun dir-locals-collect-variables (class-variables root variables)
   "Collect entries from CLASS-VARIABLES into VARIABLES.
 ROOT is the root directory of the project.
 Return the new variables list."
-  (let* ((file-name (buffer-file-name))
+  (let* ((file-name (or (buffer-file-name)
+                       ;; handle non-file buffers, too
+                       default-directory))
         (sub-file-name (if file-name
                             ;; FIXME: Why not use file-relative-name?
                            (substring file-name (length root)))))