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Suppose I have a directory with these files.
/foo/bar/baz/.dir-locals.el
/foo/bar/.dir-locals.el
/foo/.dir-locals.el
When I go to create a file in /foo/bar/baz/, I'd like to daisy chain them together such that /foo/.dir-locals.el applies first, and then /foo/bar/.dir-locals.el, and then /foo/bar/baz/.dir-locals.el
Based on the answer here, we do this by advising hack-dir-local-variables to look one directory up and load check if that .dir-locals.el file is readable. It will keep going up until it finds a directory with no readable .dir-locals.el.
Depending on the value of walk-dir-locals-upward the files can be read from the current directory upward or from the last .dir-locals.el found downward. Downward is the default so that subdirectories can clobber the settings of their parents.
(defvar walk-dir-locals-upward nil
"If non-nil, evaluate .dir-locals.el files starting in the
current directory and going up. Otherwise they will be
evaluated from the top down to the current directory.")
(defadvice hack-dir-local-variables (around walk-dir-locals-file activate)
(let* ((dir-locals-list (list dir-locals-file))
(walk-dir-locals-file (first dir-locals-list)))
(while (file-readable-p (concat "../" walk-dir-locals-file))
(progn
(setq walk-dir-locals-file (concat "../" walk-dir-locals-file))
(add-to-list 'dir-locals-list walk-dir-locals-file
walk-dir-locals-upward)
))
(dolist (file dir-locals-list)
(let ((dir-locals-file (expand-file-name file)))
(message dir-locals-file)
ad-do-it
)))
)
.dir-locals.el. Will it work if I have a tree of directories a/b/c and there exist a/.dir-locals.el and a/b/c/.dir-locals.el, but no a/b/.dir-locals.el (assume that I'm visiting a/b/c/foo.el and I want settings from a/.dir-locals.el to be applied)?
Dec 18, 2014 at 17:48
a/b/ breaks the chain. It has to stop somewhere and if you want it to keep going you can add an empty dir-locals files.
Dec 18, 2014 at 17:58
Here's a different way of doing this.
I define a function that produces the list of all the directories in the current directory hierarchy.
(defun file-name-directory-nesting-helper (name previous-name accumulator)
(if (string= name previous-name)
accumulator ; stop when names stop changing (at the top)
(file-name-directory-nesting-helper
(directory-file-name (file-name-directory name))
name
(cons name accumulator))))
(defun file-name-directory-nesting (name)
(file-name-directory-nesting-helper (expand-file-name name) "" ()))
An example is in order:
(file-name-directory-nesting "/foo/bar/baz/quux/foo.el")
;; => ("/" "/foo" "/foo/bar" "/foo/bar/baz" "/foo/bar/baz/quux" "/foo/bar/baz/quux/foo.el")
Now I can add advice to hack-dir-local-variables to make it
"pretend" that we're visiting a file at the very top of the tree,
apply directory-local settings, then step one level down, apply
settings again, and so on.
(defun hack-dir-local-variables-chained-advice (orig)
"Apply dir-local settings from the whole directory hierarchy,
from the top down."
(let ((original-buffer-file-name (buffer-file-name))
(nesting (file-name-directory-nesting (or (buffer-file-name)
default-directory))))
(unwind-protect
(dolist (name nesting)
;; make it look like we're in a directory higher up in the
;; hierarchy; note that the file we're "visiting" does not
;; have to exist
(setq buffer-file-name (expand-file-name "ignored" name))
(funcall orig))
;; cleanup
(setq buffer-file-name original-buffer-file-name))))
(advice-add 'hack-dir-local-variables :around
#'hack-dir-local-variables-chained-advice)
.dir-locals?.