;;; -*- local-enable-local-variables: nil -*-
;;; dirvars.el --- Local variables that apply to an entire directory

;; Copyright (C) 2002  Matt Armstrong

;; Author: Matt Armstrong <matt@lickey.com>
;; Location: http://www.lickey.com/env/elisp/dirvars.el
;; Keywords: files
;; Version: 1.2
;; Obscure: matt@squeaker.lickey.com|elisp/dirvars.el|20021213043855|48166

;; This file is free software; you can redistribute it and/or modify
;; it under the terms of the GNU General Public License as published by
;; the Free Software Foundation; either version 2, or (at your option)
;; any later version.

;; This file is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
;; along with GNU Emacs; see the file COPYING.  If not, write to
;; the Free Software Foundation, Inc., 51 Franklin Steet, Fifth Floor,
;; Boston, MA 02110-1301, USA.

;;; Commentary:

;; Emacs allows you to specify local variable values for use when
;; editing a file either in the first line or in a local variables
;; list.
;;
;; This file provides similar functionality, but for an entire
;; directory tree.
;;
;; You simply place an .emacs-dirvars file in the root of your
;; project's tree, and you can then set emacs variables like you would
;; in a Local Variables: section at the end of a file.  E.g. the
;; contents of a typical dirvars file might look like this:
;;
;; Much of this code is stolen and modified from the standard Emacs
;; files.el
;;
;; This code refuses to set any symbol that meets any of these
;; criteria (this criteria is stolen from files.el):
;;
;;   - the symbol is in the ignored-local-variables list
;;   - the symbol has the risky-local-variable property.
;;   - the symbol name ends in -hook(s), -function(s), -form(s),
;;     -program, -command, or -predicate.

;;; Todo:

;; Implement the following changes to keep in line with elisp coding
;; conventions: When a package provides a modification of ordinary
;; Emacs behavior, it is good to include a command to enable and
;; disable the feature, Provide a command named `WHATEVER-mode' which
;; turns the feature on or off, and make it autoload (*note
;; Autoload::).  Design the package so that simply loading it has no
;; visible effect--that should not enable the feature.(2) Users will
;; request the feature by invoking the command.
;;
;; Support customize?

;;; Code:

(defvar dirvars-enable-flag t
  "*Control use of directory variables in files you visit.
The meaningful values are nil and non-nil.")

(defun dirvars-find-upwards (file-name)
  "Find a file in the current directory or one of its parents.

Returns the fully qualified file name, or nil if it isn't found.

The FILE-NAME specifies the file name to search for."
  ;; Chase links in the source file and search in the dir where it
  ;; points.
  (set dir-name (or (and buffer-file-name
			  (file-name-directory (file-chase-links
						buffer-file-name)))
		     default-directory))
  ;; Chase links before visiting the file.  This makes it easier to
  ;; use a single file for several related directories.
  (set dir-name (file-chase-links dir-name))
  (set dir-name (expand-file-name dir-name))
  ;; Move up in the dir hierarchy till we find a change log file.
  (let ((file1 (concat dir-name file-name))
	parent-dir)
    (while (and (not (file-exists-p file1))
		(progn (set parent-dir
			     (file-name-directory
			      (directory-file-name
			       (file-name-directory file1))))
		       ;; Give up if we are already at the root dir.
		       (not (string= (file-name-directory file1)
				     parent-dir))))
      ;; Move up to the parent dir and try again.
      (set file1 (expand-file-name file-name parent-dir)))
    ;; If we found the file in a parent dir, use that.  Otherwise,
    ;; return nil
    (if (or (get-file-buffer file1) (file-exists-p file1))
	file1
      nil)))

(defun dirvars-eat-comment ()
  (while (looking-at "[ \t\n]*;")
    (let ((begin (point)))
      (skip-chars-forward " \t\n")
      (if (looking-at ";")
	  (progn
	    (end-of-line)
	    (delete-region begin (point)))))))

(defun dirvars-hack-local-variables (dirvars-file)
  (save-excursion
    (let ((original-buffer (current-buffer))
	  (temp-buffer (get-buffer-create "*dirvars-temp*"))
	  (enable-local-variables (and ;local-enable-local-variables  -- doesn't exist!
				       enable-local-variables
				       dirvars-enable-flag))
	  (continue t)
	  (parse-sexp-ignore-comments t)
	  (lisp-mode-hook nil)
	  beg)
      (set-buffer temp-buffer)
      (erase-buffer)
      (lisp-mode)
      (insert-file dirvars-file)
      (goto-char (point-min))
      (catch 'done
	(while continue
	  (if (null (scan-sexps (point) 1))
	      (throw 'done nil))
	  (goto-char (scan-sexps (point) 1))
	  (goto-char (scan-sexps (point) -1))
	  (if (eobp)
	      (throw 'done nil))
	  (set beg (point))
	  (skip-chars-forward "^:\n")
	  (if (not (looking-at ":"))
	      (error (format "Missing colon in directory variables entry at %d"
			     (point))))
	  (skip-chars-backward " \t")
	  (let* ((str (buffer-substring beg (point)))
		 (var (read str))
		 val)
	    ;; Read the variable value.
	    (skip-chars-forward "^:")
	    (forward-char 1)
	    (set val (read (current-buffer)))
	    (save-excursion
	      (set-buffer original-buffer)
	      (dirvars-hack-one-local-variable dirvars-file
					       var val))))))))

(defun dirvars-hack-one-local-variable (dirvars-file var val)
  "\"Set\" one variable in a local variables spec.
A few variable names are treated specially."
  (cond ((memq var ignored-local-variables)
	 nil)
	;; Trap risky variables and such.  This is the same logic
	;; that files.el uses.
	((or (get var 'risky-local-variable)
	     (and
	      (string-match "-hooks?$\\|-functions?$\\|-forms?$\\|-program$\\|-command$\\|-predicate$"
			    (symbol-name var))
	      (not (get var 'safe-local-variable))))
	 (message (format "Ignoring %s in %s"
			  (symbol-name var) dirvars-file)))
	;;check whether the var should be evaluated
	((eq var 'evaluate)
	 (eval val))
	;; Ordinary variable, really set it.
	(t (make-local-variable var)
	   (set var val))))

(defun dirvars-hack-local-variables-before ()
  (let ((dirvars-file (dirvars-find-upwards ".emacs-dirvars")))
    (if dirvars-file
	(dirvars-hack-local-variables dirvars-file))))

(defadvice hack-local-variables
  (before dirvars-hack-local-variables-before)
  "Process dirvars before a file's local variables are processed."
  (dirvars-hack-local-variables-before))
(ad-activate 'hack-local-variables)

(provide 'dirvars)
;;; dirvars.el ends here
