bug#2833: 23.0.92; Bug in Directory Variables

[Chong Yidong]

The following patch changes the directory local variables code so that
the cache stores the file atime.  Before using each cache entry, we
check that against the file modtime.

This is not an ideal time to make changes of this sort, but I think this
problem (i.e., inability to detect changes in .dir-locals.el files) is
quite a serious one.  So please help me review this patch.

*** trunk/lisp/files.el.~1.1044.~       2009-04-08 10:42:40.000000000 -0400
--- trunk/lisp/files.el 2009-04-08 22:50:03.000000000 -0400
***************
*** 3187,3194 ****
  (defvar dir-locals-class-alist '()
    "Alist mapping class names (symbols) to variable lists.")
  
! (defvar dir-locals-directory-alist '()
!   "Alist mapping directory roots to variable classes.")
  
  (defsubst dir-locals-get-class-variables (class)
    "Return the variable list for CLASS."
--- 3187,3199 ----
  (defvar dir-locals-class-alist '()
    "Alist mapping class names (symbols) to variable lists.")
  
! (defvar dir-locals-directory-cache '()
!   "List of cached directory roots for directory-local variable files.
! Each element in this list has the form (DIR ATIME CLASS), where
! DIR is the name of the directory, ATIME is the time when this
! cache entry was created (as a floating point number, per
! `float-time'), and CLASS is the name of a project class (a
! symbol).")
  
  (defsubst dir-locals-get-class-variables (class)
    "Return the variable list for CLASS."
***************
*** 3241,3247 ****
    (setq directory (file-name-as-directory (expand-file-name directory)))
    (unless (assq class dir-locals-class-alist)
      (error "No such class `%s'" (symbol-name class)))
!   (push (cons directory class) dir-locals-directory-alist))
  
  (defun dir-locals-set-class-variables (class variables)
    "Map the type CLASS to a list of variable settings.
--- 3246,3252 ----
    (setq directory (file-name-as-directory (expand-file-name directory)))
    (unless (assq class dir-locals-class-alist)
      (error "No such class `%s'" (symbol-name class)))
!   (push (list directory (float-time) class) dir-locals-directory-cache))
  
  (defun dir-locals-set-class-variables (class variables)
    "Map the type CLASS to a list of variable settings.
***************
*** 3284,3295 ****
  across different environments and users.")
  
  (defun dir-locals-find-file (file)
!   "Find the directory-local variables FILE.
! This searches upward in the directory tree.
! If a local variables file is found, the file name is returned.
! If the file is already registered, a cons from
! `dir-locals-directory-alist' is returned.
! Otherwise this returns nil."
    (setq file (expand-file-name file))
    (let* ((dir-locals-file-name
          (if (eq system-type 'ms-dos)
--- 3289,3304 ----
  across different environments and users.")
  
  (defun dir-locals-find-file (file)
!   "Find the directory-local variables for FILE.
! This searches upward in the directory tree from FILE.
! 
! If the file is already registered and has not been modified since
!  we added it to `dir-locals-directory-cache', this returns a cons
!  cell of the form (DIRECTORY . CLASS), using the entry in
!  `dir-locals-directory-cache'.
! Otherwise, if a local variables file is found, the file name is
!  returned.
! Otherwise, this returns nil."
    (setq file (expand-file-name file))
    (let* ((dir-locals-file-name
          (if (eq system-type 'ms-dos)
***************
*** 3300,3318 ****
      ;; `locate-dominating-file' may have abbreviated the name.
      (when locals-file
        (setq locals-file (expand-file-name dir-locals-file-name locals-file)))
!     (dolist (elt dir-locals-directory-alist)
        (when (and (eq t (compare-strings file nil (length (car elt))
                                        (car elt) nil nil
                                        (memq system-type
                                              '(windows-nt cygwin ms-dos))))
                 (> (length (car elt)) (length (car dir-elt))))
        (setq dir-elt elt)))
!     (if (and locals-file dir-elt)
!       (if (> (length (file-name-directory locals-file))
!              (length (car dir-elt)))
!           locals-file
!         dir-elt)
!       (or locals-file dir-elt))))
  
  (defun dir-locals-read-from-file (file)
    "Load a variables FILE and register a new class and instance.
--- 3309,3338 ----
      ;; `locate-dominating-file' may have abbreviated the name.
      (when locals-file
        (setq locals-file (expand-file-name dir-locals-file-name locals-file)))
!     ;; Find the best cached value in `dir-locals-directory-cache'.
!     (dolist (elt dir-locals-directory-cache)
        (when (and (eq t (compare-strings file nil (length (car elt))
                                        (car elt) nil nil
                                        (memq system-type
                                              '(windows-nt cygwin ms-dos))))
                 (> (length (car elt)) (length (car dir-elt))))
        (setq dir-elt elt)))
!     (let ((use-cache (and dir-elt
!                         (or (null locals-file)
!                             (<= (length (file-name-directory locals-file))
!                                 (length (car dir-elt)))))))
!       (if use-cache
!         ;; Check the validity of the cache.
!         (if (and (file-readable-p (car dir-elt))
!                  (< (float-time (nth 5 (file-attributes (car dir-elt))))
!                     (nth 1 dir-elt)))
!             ;; This cache entry is OK.
!             (cons (nth 0 dir-elt) (nth 2 dir-elt))
!           ;; This cache entry is invalid; clear it.
!           (setq dir-locals-directory-cache
!                 (delq dir-elt dir-locals-directory-cache))
!           locals-file)
!       locals-file))))
  
  (defun dir-locals-read-from-file (file)
    "Load a variables FILE and register a new class and instance.