;;; shadow.el --- Locate Emacs Lisp file shadowings.

;; Copyright (C) 1995 Free Software Foundation, Inc.

;; Author: Terry Jones <terry@santafe.edu>
;; Keywords: lisp
;; Created: 15 December 1995

;; This file is part of XEmacs.

;; XEmacs 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 3 of the License, or (at your
;; option) any later version.

;; XEmacs 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 XEmacs.  If not, see <http://www.gnu.org/licenses/>.

;;; Commentary:

;; The functions in this file detect (`find-emacs-lisp-shadows')
;; and display (`list-load-path-shadows') potential load-path
;; problems that arise when Emacs Lisp files "shadow" each other.
;;
;; For example, a file XXX.el early in one's load-path will shadow
;; a file with the same name in a later load-path directory.  When
;; this is unintentional, it may result in problems that could have
;; been easily avoided.  This occurs often (to me) when installing a
;; new version of emacs and something in the site-lisp directory
;; has been updated and added to the emacs distribution.  The old
;; version, now outdated, shadows the new one. This is obviously
;; undesirable.
;;
;; The `list-load-path-shadows' function was run when you installed
;; this version of emacs. To run it by hand in emacs:
;;
;;     M-x load-library RET shadow RET
;;     M-x list-load-path-shadows
;;
;; or run it non-interactively via:
;;
;;     emacs -batch -l shadow.el -f list-load-path-shadows
;;
;; Thanks to Francesco Potorti` <pot@cnuce.cnr.it> for suggestions,
;; rewritings & speedups.

;; 1998-08-15 Martin Buchholz: Speed up using hash tables instead of lists.

;;; Code:

(defun find-emacs-lisp-shadows (&optional path)
  "Return a list of Emacs Lisp files that create shadows.
This function does the work for `list-load-path-shadows'.

We traverse PATH looking for shadows, and return a \(possibly empty\)
even-length list of files.  A file in this list at position 2i shadows
the file in position 2i+1.  Emacs Lisp file suffixes \(.el and .elc\)
are stripped from the file names in the list.

See the documentation for `list-load-path-shadows' for further information."
  
  (let (shadows				; List of shadowings, to be returned.
	dir				; The dir being currently scanned.
	curr-files			; This dir's Emacs Lisp files.
	orig-dir			; Where the file was first seen.
	(file-dirs			; File names ever seen, with dirs.
	 (make-hash-table :size 2000 :test 'equal))
	(true-names			; Dirs ever considered.
	 (make-hash-table :size 50 :test 'equal))
	(files-seen-this-dir		; Files seen so far in this dir.
	 (make-hash-table :size 100 :test 'equal))
	)
  
    (dolist (path-elt (or path load-path))

      (setq dir (file-truename (or path-elt ".")))
      (if (gethash dir true-names)
	  ;; We have already considered this PATH redundant directory.
	  ;; Show the redundancy if we are interactive, unless the PATH
	  ;; dir is nil or "." (these redundant directories are just a
	  ;; result of the current working directory, and are therefore
	  ;; not always redundant).
	  (or noninteractive
	      (and path-elt
		   (not (string= path-elt "."))
		   (message "Ignoring redundant directory %s" path-elt)))

	(puthash dir t true-names)
	(setq dir (or path-elt "."))
	(setq curr-files (if (file-accessible-directory-p dir)
                               (directory-files dir nil ".\\.elc?$" t)))
	(and curr-files
	     (not noninteractive)
	     (message "Checking %d files in %s..." (length curr-files) dir))
	
	(clrhash files-seen-this-dir)

	(dolist (file curr-files)

	  (setq file (substring
		      file 0 (if (string= (substring file -1) "c") -4 -3)))

	  ;; FILE now contains the current file name, with no suffix.
	  (unless (or (gethash file files-seen-this-dir)
		      ;; Ignore these files.
		      (member file
			      '("subdirs"
				"auto-autoloads"
				"custom-load"
				"custom-defines"
				"dumped-lisp"
				"_pkg"
				"lpath")))
	    ;; File has not been seen yet in this directory.
	    ;; This test prevents us declaring that XXX.el shadows
	    ;; XXX.elc (or vice-versa) when they are in the same directory.
	    (puthash file t files-seen-this-dir)
	      
	    (if (setq orig-dir (gethash file file-dirs))
		;; This file was seen before, we have a shadowing.
		(setq shadows
		      (nconc shadows
			     (list (concat (file-name-as-directory orig-dir)
					   file)
				   (concat (file-name-as-directory dir)
					   file))))

	      ;; Not seen before, add it to the list of seen files.
	      (puthash file dir file-dirs))))))

    ;; Return the list of shadowings.
    shadows))


;;;###autoload
(defun list-load-path-shadows ()
  "Display a list of Emacs Lisp files that shadow other files.

This function lists potential load-path problems.  Directories in the
`load-path' variable are searched, in order, for Emacs Lisp
files.  When a previously encountered file name is found again, a
message is displayed indicating that the later file is \"hidden\" by
the earlier.

For example, suppose `load-path' is set to

\(\"/usr/gnu/emacs/site-lisp\" \"/usr/gnu/emacs/share/emacs/19.30/lisp\"\)

and that each of these directories contains a file called XXX.el.  Then
XXX.el in the site-lisp directory is referred to by all of:
\(require 'XXX\), \(autoload .... \"XXX\"\), \(load-library \"XXX\"\) etc.

The first XXX.el file prevents emacs from seeing the second \(unless
the second is loaded explicitly via load-file\).

When not intended, such shadowings can be the source of subtle
problems.  For example, the above situation may have arisen because the
XXX package was not distributed with versions of emacs prior to
19.30.  An emacs maintainer downloaded XXX from elsewhere and installed
it.  Later, XXX was updated and included in the emacs distribution.
Unless the emacs maintainer checks for this, the new version of XXX
will be hidden behind the old \(which may no longer work with the new
emacs version\).

This function performs these checks and flags all possible
shadowings.  Because a .el file may exist without a corresponding .elc
\(or vice-versa\), these suffixes are essentially ignored.  A file
XXX.elc in an early directory \(that does not contain XXX.el\) is
considered to shadow a later file XXX.el, and vice-versa.

When run interactively, the shadowings \(if any\) are displayed in a
buffer called `*Shadows*'.  Shadowings are located by calling the
\(non-interactive\) companion function, `find-emacs-lisp-shadows'."
  
  (interactive)
  (let* ((path (copy-sequence load-path))
	(tem path)
	toplevs)
    ;; If we can find simple.el in two places,
    (while tem
      (if (file-exists-p (expand-file-name "simple.el" (car tem)))
	  (setq toplevs (cons (car tem) toplevs)))
      (setq tem (cdr tem)))
    (if (> (length toplevs) 1)
	;; Cut off our copy of load-path right before
	;; the second directory which has simple.el in it.
	;; This avoids loads of duplications between the source dir
	;; and the dir where these files were copied by installation.
	(let ((break (nth (- (length toplevs) 2) toplevs)))
	  (setq tem path)
	  (while tem
	    (if (eq (nth 1 tem) break)
		(progn
		  (setcdr tem nil)
		  (setq tem nil)))
	    (setq tem (cdr tem)))))

    (let* ((shadows (find-emacs-lisp-shadows path))
	   (n (/ (length shadows) 2))
	   (msg (format "%s Emacs Lisp load-path shadowing%s found"
			(if (zerop n) "No" (concat "\n" (number-to-string n)))
			(if (= n 1) " was" "s were"))))
      (if (interactive-p)
	  (save-excursion
	    ;; We are interactive.
	    ;; Create the *Shadows* buffer and display shadowings there.
	    (let ((output-buffer (get-buffer-create "*Shadows*")))
	      (display-buffer output-buffer)
	      (set-buffer output-buffer)
	      (erase-buffer)
	      (while shadows
		(insert (format "%s hides %s\n" (car shadows)
				(car (cdr shadows))))
		(setq shadows (cdr (cdr shadows))))
	      (insert msg "\n")))
	;; We are non-interactive, print shadows via message.
	(when shadows
	  (message "This site has duplicate Lisp libraries with the same name.
If a locally-installed Lisp library overrides a library in the Emacs release,
that can cause trouble, and you should probably remove the locally-installed
version unless you know what you are doing.\n")
	  (while shadows
	    (message "%s hides %s" (car shadows) (car (cdr shadows)))
	    (setq shadows (cdr (cdr shadows))))
	  (message "%s" msg))))))

(provide 'shadow)

;;; shadow.el ends here