;;; ffap.el --- find file (or url) at point  -*- lexical-binding: t -*-

;; Copyright (C) 1995-2024 Free Software Foundation, Inc.

;; Author: Michelangelo Grigni <mic@mathcs.emory.edu>
;; Maintainer: emacs-devel@gnu.org
;; Created: 29 Mar 1993
;; Keywords: files, hypermedia, matching, mouse, convenience

;; This file is part of GNU Emacs.

;; GNU Emacs 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.

;; GNU Emacs 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.  If not, see <https://www.gnu.org/licenses/>.

\f
;;; Commentary:

;; Command `find-file-at-point' replaces `find-file'.  With a prefix,
;; it behaves exactly like find-file.  Without a prefix, it first
;; tries to guess a default file or URL from the text around the point
;; (`ffap-require-prefix' swaps these behaviors).  This is useful for
;; following references in situations such as mail or news buffers,
;; README's, MANIFEST's, and so on.  Submit bugs or suggestions with
;; `M-x report-emacs-bug'.
;;
;; For the default installation, add this line to your init file:
;;
;; (ffap-bindings)                      ; do default key bindings
;;
;; ffap-bindings makes the following global key bindings:
;;
;; C-x C-f		find-file-at-point (abbreviated as ffap)
;; C-x C-r		ffap-read-only
;; C-x C-v		ffap-alternate-file
;;
;; C-x d		dired-at-point
;; C-x C-d		ffap-list-directory
;;
;; C-x 4 f		ffap-other-window
;; C-x 4 r		ffap-read-only-other-window
;; C-x 4 d		ffap-dired-other-window
;;
;; C-x 5 f		ffap-other-frame
;; C-x 5 r		ffap-read-only-other-frame
;; C-x 5 d		ffap-dired-other-frame
;;
;; C-x t f		ffap-other-tab
;;
;; S-mouse-3     ffap-at-mouse
;; C-S-mouse-3   ffap-menu
;;
;; ffap-bindings also adds hooks to make the following local bindings
;; in vm, gnus, and rmail:
;;
;; M-l         ffap-next, or ffap-gnus-next in gnus (l == "link")
;; M-m         ffap-menu, or ffap-gnus-menu in gnus (m == "menu")
;;
;; If you do not like these bindings, modify the variable
;; `ffap-bindings', or write your own.
;;
;; If you use ange-ftp, it is best to load or autoload it before ffap.
;; If you use ff-paths, load it afterwards.  Try apropos `C-h a ffap
;; RET' to get a list of the many option variables.  In particular, if
;; ffap is slow, try these:
;;
;; (setq ffap-alist nil)                ; faster, dumber prompting
;; (setq ffap-url-regexp nil)           ; disable URL features in ffap
;; (setq ffap-shell-prompt-regexp nil)  ; disable shell prompt stripping
;; (setq ffap-gopher-regexp nil)        ; disable gopher bookmark matching
;;
;; ffap uses `browse-url' to fetch URLs.
;; Also, you can add `ffap-menu-rescan' to various hooks to fontify
;; the file and URL references within a buffer.

\f
;;; Code:

;;; Change Log:
;; The History and Contributors moved to ffap.LOG, which also has some
;; old examples and commentary from ffap 1.5.

;;; Todo list:
;; * let "/dir/file#key" jump to key (tag or regexp) in /dir/file
;; * find file of symbol if TAGS is loaded (like above)
;; * break long menus into multiple panes (like imenu?)
;; * notice node in "(dired)Virtual Dired" (quotes, parentheses, whitespace)
;; * notice "machine.dom blah blah blah dir/file" (how?)
;; * regexp options for ffap-string-at-point, like font-lock (MCOOK)
;; * could replace `ffap-locate-file' with a quieter `locate-library'
;; * handle "$(VAR)" in Makefiles
;; * use the font-lock machinery

(eval-when-compile (require 'cl-lib))
(require 'url-parse)
(require 'thingatpt)

(defgroup ffap nil
  "Find file or URL at point."
  :group 'matching
  :group 'convenience)

\f
;;; User Variables:

(defun ffap-symbol-value (sym &optional default)
  "Return value of symbol SYM, if bound, or DEFAULT otherwise."
  (if (boundp sym) (symbol-value sym) default))

(defcustom ffap-shell-prompt-regexp
  ;; This used to test for some shell prompts that don't have a space
  ;; after them. The common root shell prompt (#) is not listed since it
  ;; also doubles up as a valid URL character.
  "[$%><]*"
  "Paths matching this regexp are stripped off the shell prompt.
If nil, ffap doesn't do shell prompt stripping."
  :type '(choice (const :tag "Disable" nil)
		  (const :tag "Standard" "[$%><]*")
		   regexp)
  :group 'ffap)

(defcustom ffap-ftp-regexp "\\`/[^/:]+:"
  "File names matching this regexp are treated as remote ffap.
If nil, ffap neither recognizes nor generates such names."
  :type '(choice (const :tag "Disable" nil)
		 (const :tag "Standard" "\\`/[^/:]+:")
		 regexp)
  :group 'ffap)

(defcustom ffap-url-unwrap-local t
  "If non-nil, convert some URLs to local file names before prompting.
Only \"file:\" and \"ftp:\" URLs are converted, and only if they
do not specify a host, or the host is either \"localhost\" or
equal to `system-name'."
  :type 'boolean
  :group 'ffap)

(defcustom ffap-url-unwrap-remote '("ftp")
  "If non-nil, convert URLs to remote file names before prompting.
If the value is a list of strings, that specifies a list of URL
schemes (e.g. \"ftp\"); in that case, only convert those URLs."
  :type '(choice (repeat string) boolean)
  :group 'ffap
  :version "24.3")

(defcustom ffap-lax-url nil
  "If non-nil, allow lax URL matching.
The default non-nil value might produce false URLs in C++ code
with symbols like \"std::find\".  On the other hand, setting
this to nil will disable recognition of URLs that are not
well-formed."
  :type 'boolean
  :group 'ffap
  :version "30.1")

(defcustom ffap-ftp-default-user "anonymous"
  "User name in FTP file names generated by `ffap-host-to-filename'.
Note this name may be omitted if it equals the default
(`ange-ftp-default-user')."
  :type 'string
  :group 'ffap)

(defcustom ffap-rfs-regexp
  ;; Remote file access built into file system?  HP rfa or Andrew afs:
  "\\`/\\(afs\\|net\\)/."
  ;; afs only: (and (file-exists-p "/afs") "\\`/afs/.")
  "Matching file names are treated as remote.  Use nil to disable."
  :type '(choice (const :tag "Disable" nil)
                 regexp)
  :group 'ffap)

(defvar ffap-url-regexp
  (concat
   "\\("
   "news\\(post\\)?:\\|mailto:\\|file:" ; no host ok
   "\\|"
   "\\(ftp\\|https?\\|telnet\\|gopher\\|gemini\\|www\\|wais\\)://" ; needs host
   "\\)")
  "Regexp matching the beginning of a URI, for ffap.
If the value is nil, disable URL-matching features in ffap.")

(defcustom ffap-foo-at-bar-prefix "mailto"
  "Presumed URL prefix type of strings like \"<foo.9z@bar>\".
Sensible values are nil, \"news\", or \"mailto\"."
  :type '(choice (const "mailto")
		 (const "news")
		 (const :tag "Disable" nil)
		 ;; string -- possible, but not really useful
		 )
  :group 'ffap)

(defvar ffap-max-region-length 1024
  "Maximum active region length.
When the region is active and larger than this value,
`ffap-string-at-point' returns an empty string.")

\f
;;; Peanut Gallery (More User Variables):
;;
;; Users of ffap occasionally suggest new features.  If I consider
;; those features interesting but not clear winners (a matter of
;; personal taste) I try to leave options to enable them.  Read
;; through this section for features that you like, put an appropriate
;; enabler in your init file.

(defcustom ffap-dired-wildcards "[*?][^/]*\\'"
  "A regexp matching filename wildcard characters, or nil.

If `find-file-at-point' gets a filename matching this pattern,
and `ffap-pass-wildcards-to-dired' is nil, it passes it on to
`find-file' with non-nil WILDCARDS argument, which expands
wildcards and visits multiple files.  To visit a file whose name
contains wildcard characters you can suppress wildcard expansion
by setting `find-file-wildcards'.  If `find-file-at-point' gets a
filename matching this pattern and `ffap-pass-wildcards-to-dired'
is non-nil, it passes it on to `dired'.

If `dired-at-point' gets a filename matching this pattern,
it passes it on to `dired'."
  :type '(choice (const :tag "Disable" nil)
		 (const :tag "Enable" "[*?][^/]*\\'")
		 ;; regexp -- probably not useful
		 )
  :group 'ffap)

(defcustom ffap-pass-wildcards-to-dired nil
  "If non-nil, pass filenames matching `ffap-dired-wildcards' to Dired."
  :type 'boolean
  :group 'ffap)

(defcustom ffap-newfile-prompt nil
  "Whether `find-file-at-point' prompts about a nonexistent file."
  :type 'boolean
  :group 'ffap)
(make-obsolete-variable 'ffap-newfile-prompt 'find-file-not-found-functions "29.1")

(defcustom ffap-require-prefix nil
  "If set, reverses the prefix argument to `find-file-at-point'.
This is nil so neophytes notice ffap.  Experts may prefer to disable
ffap most of the time."
  :type 'boolean
  :group 'ffap)

;;;###autoload
(defcustom ffap-file-finder #'find-file
  "The command called by `find-file-at-point' to find a file."
  :type 'function
  :group 'ffap
  :risky t)

(defcustom ffap-directory-finder #'dired
  "The command called by `dired-at-point' to find a directory."
  :type 'function
  :group 'ffap
  :risky t)

(defcustom ffap-url-fetcher #'browse-url
  "A function of one argument, called by ffap to fetch an URL."
  :type '(choice (const browse-url)
		 function)
  :group 'ffap
  :risky t)

(defcustom ffap-next-regexp
  ;; If you want ffap-next to find URLs only, try this:
  ;; (and ffap-url-regexp (string-match "\\\\`" ffap-url-regexp)
  ;;	  (concat "\\<" (substring ffap-url-regexp 2))))
  ;;
  ;; It pays to put a big fancy regexp here, since ffap-guesser is
  ;; much more time-consuming than regexp searching:
  "[/:.~[:alpha:]]/\\|@[[:alpha:]][-[:alnum:]]*\\."
  "Regular expression governing movements of `ffap-next'."
  :type 'regexp
  :group 'ffap)

(defcustom dired-at-point-require-prefix nil
  "If non-nil, reverse the prefix argument to `dired-at-point'.
This is nil so neophytes notice ffap.  Experts may prefer to
disable ffap most of the time."
  :type 'boolean
  :group 'ffap
  :version "20.3")

\f
;;; Obsolete:

(defun ffap-mouse-event ()		; current mouse event, or nil
  (declare (obsolete nil "28.1"))
  (and (listp last-nonmenu-event) last-nonmenu-event))

(defun ffap-event-buffer (event)
  (declare (obsolete nil "28.1"))
  (window-buffer (car (event-start event))))

\f
;;; Find Next Thing in buffer (`ffap-next'):

(defvar ffap-next-guess nil
  "Last value returned by `ffap-next-guess'.")

(defvar ffap-string-at-point-region '(1 1)
  "List (BEG END), last region returned by the function `ffap-string-at-point'.")

(defun ffap-next-guess (&optional back lim)
  "Move point to next file or URL, and return it as a string.
If nothing is found, leave point at limit and return nil.
Optional BACK argument makes search backwards.
Optional LIM argument limits the search.
Only considers strings that match `ffap-next-regexp'."
  (or lim (setq lim (if back (point-min) (point-max))))
  (let (guess)
    (while (not (or guess (eq (point) lim)))
      (funcall (if back 're-search-backward 're-search-forward)
	       ffap-next-regexp lim 'move)
      (setq guess (ffap-guesser)))
    ;; Go to end, so we do not get same guess twice:
    (goto-char (nth (if back 0 1) ffap-string-at-point-region))
    (setq ffap-next-guess guess)))

;;;###autoload
(defun ffap-next (&optional back wrap)
  "Search buffer for next file or URL, and run ffap.
Optional argument BACK says to search backwards.
Optional argument WRAP says to try wrapping around if necessary.
Interactively: use a single prefix \\[universal-argument] to search backwards,
double prefix to wrap forward, triple to wrap backwards.
Actual search is done by the function `ffap-next-guess'."
  (interactive
   (cdr (assq (prefix-numeric-value current-prefix-arg)
	      '((1) (4 t) (16 nil t) (64 t t)))))
  (let ((pt (point))
	(guess (ffap-next-guess back)))
    ;; Try wraparound if necessary:
    (and (not guess) wrap
	 (goto-char (if back (point-max) (point-min)))
	 (setq guess (ffap-next-guess back pt)))
    (if guess
	(progn
	  (sit-for 0)			; display point movement
	  (find-file-at-point (ffap-prompter guess)))
      (goto-char pt)			; restore point
      (message "No %sfiles or URLs found"
	       (if wrap "" "more ")))))

(defun ffap-next-url (&optional back wrap)
  "Like `ffap-next', but search with `ffap-url-regexp'."
  (interactive)
  (let ((ffap-next-regexp ffap-url-regexp))
    (if (called-interactively-p 'interactive)
	(call-interactively 'ffap-next)
      (ffap-next back wrap))))

\f
;;; Machines (`ffap-machine-p'):

(defun ffap-accept-or-reject-p (symbol)
  "Return non-nil if SYMBOL is `accept' or `reject'.
Otherwise, return nil.  This is intended for use as the
predicate in the `:safe' property of user options."
  (memq symbol '(accept reject)))

;; I cannot decide a "best" strategy here, so these are variables.  In
;; particular, if `Pinging...' is broken or takes too long on your
;; machine, try setting these all to accept or reject.
(defcustom ffap-machine-p-local 'reject	; this happens often
  "What `ffap-machine-p' does with hostnames that have no domain.
Value should be a symbol, one of `ping', `accept', and `reject'."
  :type '(choice (const ping)
		 (const accept)
                 (const reject))
  :safe #'ffap-accept-or-reject-p
  :group 'ffap)

(defcustom ffap-machine-p-known 'accept
  "What `ffap-machine-p' does with hostnames that have a known domain.
Value should be a symbol, one of `ping', `accept', and `reject'.
See `mail-extr.el' for the known domains."
  :type '(choice (const ping)
		 (const accept)
                 (const reject))
  :safe #'ffap-accept-or-reject-p
  :group 'ffap
  :version "29.1")

(defcustom ffap-machine-p-unknown 'reject
  "What `ffap-machine-p' does with hostnames that have an unknown domain.
Value should be a symbol, one of `ping', `accept', and `reject'.
See `mail-extr.el' for the known domains."
  :type '(choice (const ping)
		 (const accept)
		 (const reject))
  :safe #'ffap-accept-or-reject-p
  :group 'ffap)

(defun ffap-what-domain (domain)
  ;; Like what-domain in mail-extr.el, returns string or nil.
  (require 'mail-extr)
  (let ((ob (ffap-symbol-value 'mail-extr-all-top-level-domains)))
    (and ob (get (intern-soft (downcase domain) ob) 'domain-name))))

(defun ffap-machine-p (host &optional service quiet strategy)
  "Decide whether HOST is the name of a real, reachable machine.
Depending on the domain (none, known, or unknown), follow the strategy
named by the variable `ffap-machine-p-local', `ffap-machine-p-known',
or `ffap-machine-p-unknown'.  Pinging uses `open-network-stream'.
Optional SERVICE specifies the port used (default \"discard\").
Optional QUIET flag suppresses the \"Pinging...\" message.
Optional STRATEGY overrides the three variables above.
Returned values:
 t       means that HOST answered.
`accept' means the relevant variable told us to accept.
\"mesg\"   means HOST exists, but does not respond for some reason."
  (if (or (string-match "[^-[:alnum:].]" host) ; Invalid chars (?)
	  (not (string-match "[^0-9]" host))) ; 1: a number? 2: quick reject
      nil
    (let* ((domain
	    (and (string-match "\\.[^.]*$" host)
		 (downcase (substring host (1+ (match-beginning 0))))))
	   (what-domain (if domain (ffap-what-domain domain) "Local")))
      (or strategy
	  (setq strategy
		(cond ((not domain) ffap-machine-p-local)
		      ((not what-domain) ffap-machine-p-unknown)
		      (t ffap-machine-p-known))))
      (cond
       ((eq strategy 'accept) 'accept)
       ((eq strategy 'reject) nil)
       ((not (fboundp 'open-network-stream)) nil)
       ;; assume (eq strategy 'ping)
       (t
	(or quiet
	    (if (stringp what-domain)
		(message "Pinging %s (%s)..." host what-domain)
	      (message "Pinging %s ..." host)))
	(condition-case error
	    (progn
	      (delete-process
	       (open-network-stream
		"ffap-machine-p" nil host (or service "discard")))
	      t)
	  (error
	   (let ((mesg (car (cdr error))))
	     (cond
	      ;; v18:
	      ((string-match "\\(^Unknown host\\|Name or service not known$\\)"
			     mesg) nil)
	      ((string-match "not responding$" mesg) mesg)
	      ;; v19:
              ;; (file-error "Connection failed" "permission denied"
	      ;;             "nonesuch" "ffap-machine-p")
              ;; (file-error "Connection failed" "host is unreachable"
	      ;;	     "gopher.house.gov" "ffap-machine-p")
              ;; (file-error "Connection failed" "address already in use"
	      ;;	     "ftp.uu.net" "ffap-machine-p")
	      ((equal mesg "connection failed")
	       (if (string= (downcase (nth 2 error)) "permission denied")
		   nil			; host does not exist
		 ;; Other errors mean the host exists:
		 (nth 2 error)))
	      ;; Could be "Unknown service":
	      (t (signal (car error) (cdr error))))))))))))

\f
;;; Possibly Remote Resources:

(defun ffap-replace-file-component (fullname name)
  "In remote FULLNAME, replace path with NAME.  May return nil."
  (and (stringp fullname)
       (stringp name)
       (concat (file-remote-p fullname) name)))

(defun ffap-file-suffix (file)
  "Return trailing `.foo' suffix of FILE, or nil if none."
  (declare (obsolete file-name-extension "29.1"))
  (let ((pos (string-match "\\.[^./]*\\'" file)))
    (and pos (substring file pos nil))))

(defvar ffap-compression-suffixes '(".gz" ".Z")	; .z is mostly dead
  "List of suffixes tried by `ffap-file-exists-string'.")

(defun ffap-file-exists-string (file &optional nomodify)
  ;; Early jka-compr versions modified file-exists-p to return the
  ;; filename, maybe modified by adding a suffix like ".gz".  That
  ;; broke the interface of file-exists-p, so it was later dropped.
  ;; Here we document and simulate the old behavior.
  "Return FILE (maybe modified) if the file exists, else nil.
When using jka-compr (a.k.a. `auto-compression-mode'), the returned
name may have a suffix added from `ffap-compression-suffixes'.
The optional NOMODIFY argument suppresses the extra search."
  (cond
   ((or (not file)			; quietly reject nil
	(zerop (length file)))		; and also ""
    nil)
   ((file-exists-p file) file)		; try unmodified first
   ;; three reasons to suppress search:
   (nomodify nil)
   ((not (rassq 'jka-compr-handler file-name-handler-alist)) nil)
   ((member (file-name-extension file t) ffap-compression-suffixes) nil)
   (t					; ok, do the search
    (let ((list ffap-compression-suffixes) try ret)
      (while list
	(if (file-exists-p (setq try (concat file (car list))))
	    (setq ret try list nil)
	  (setq list (cdr list))))
      ret))))

(defun ffap-file-remote-p (filename)
  "If FILENAME looks remote, return it (maybe slightly improved)."
  (or (and ffap-ftp-regexp
	   (string-match ffap-ftp-regexp filename)
	   ;; Convert "/host.com://dir" to "/host:/dir", to handle a dying
	   ;; practice of advertising ftp files as "host.dom://filename".
	   (if (string-match "//" filename)
	       ;; (replace-match "/" nil nil filename)
	       (concat (substring filename 0 (1+ (match-beginning 0)))
		       (substring filename (match-end 0)))
	     filename))
      (and ffap-rfs-regexp
	   (string-match ffap-rfs-regexp filename)
	   filename)))

;;;###autoload
(defun ffap-machine-at-point ()
  "Return machine name at point if it exists, or nil."
  (let ((mach (ffap-string-at-point 'machine)))
    (and (ffap-machine-p mach) mach)))

(defsubst ffap-host-to-filename (host)
  "Convert HOST to something like \"/USER@HOST:\" or \"/HOST:\".
Looks at `ffap-ftp-default-user', returns \"\" for \"localhost\"."
  (if (equal host "localhost")
      ""
    (let ((user ffap-ftp-default-user))
      ;; Avoid including the user if it is same as default:
      (when (equal user (ffap-symbol-value 'ange-ftp-default-user))
        (setq user nil))
      (concat "/" user (and user "@") host ":"))))

(defun ffap-fixup-machine (mach)
  ;; Convert a hostname into an url, an ftp file name, or nil.
  (cond
   ((not (and ffap-url-regexp (stringp mach))) nil)
   ;; gopher.well.com
   ((string-match "\\`gopher[-.]" mach)	; or "info"?
    (concat "gopher://" mach "/"))
   ;; www.ncsa.uiuc.edu
   ((and (string-match "\\`w\\(ww\\|eb\\)[-.]" mach))
    (concat "https://" mach "/"))
   ;; More cases?
   (ffap-ftp-regexp (ffap-host-to-filename mach))
   ))

(defun ffap-url-p (string)
  "If STRING looks like an URL, return it (maybe improved), else nil."
  (when (and (stringp string) ffap-url-regexp)
    (let* ((case-fold-search t)
	   (match (string-match ffap-url-regexp string)))
      (cond ((eq match 0) string)
	    (match (substring string match))))))

;; Broke these out of ffap-fixup-url, for use of ffap-url package.
(defun ffap-url-unwrap-local (url)
  "Return URL as a local file name, or nil."
  (let* ((obj (url-generic-parse-url url))
	 (host (url-host obj))
	 (filename (car (url-path-and-query obj))))
    (when (and (member (url-type obj) '("ftp" "file"))
	       (member host `("" "localhost" ,(system-name))))
      ;; On Windows, "file:///C:/foo" should unwrap to "C:/foo"
      (if (and (memq system-type '(ms-dos windows-nt cygwin))
	       (string-match "\\`/[a-zA-Z]:" filename))
	  (substring filename 1)
	filename))))

(defun ffap-url-unwrap-remote (url)
  "Return URL as a remote file name, or nil."
  (let* ((obj    (url-generic-parse-url url))
	 (scheme (url-type obj))
	 (valid-schemes (if (listp ffap-url-unwrap-remote)
			    ffap-url-unwrap-remote
			  '("ftp")))
	 (host (url-host obj))
	 (port (url-port-if-non-default obj))
	 (user (url-user obj))
	 (filename (car (url-path-and-query obj))))
    (when (and (member scheme valid-schemes)
	       (string-match "\\`[a-zA-Z][-a-zA-Z0-9+.]*\\'" scheme)
	       (not (equal host "")))
      (concat "/" scheme ":"
	      (if user (concat user "@"))
	      host
	      (if port (concat "#" (number-to-string port)))
	      ":" filename))))

(defun ffap-fixup-url (url)
  "Clean up URL and return it, maybe as a file name."
  (cond
   ((not (stringp url)) nil)
   ((and ffap-url-unwrap-local  (ffap-url-unwrap-local url)))
   ((and ffap-url-unwrap-remote (ffap-url-unwrap-remote url)))
   (url)))

(defun ffap-fixup-email (email)
  "Clean up EMAIL and return it as a mailto: URL."
  (when (stringp email)
    (if (string-prefix-p "mailto:" email)
        email
      (concat "mailto:" email))))

\f
;;; File Name Handling:

(defun ffap-list-env (env &optional empty)
  "Return a list of strings parsed from environment variable ENV.
Optional EMPTY is the default list if (getenv ENV) is undefined, and
also is substituted for the first empty-string component, if there is one.
Uses `path-separator' to separate the path into substrings."
  ;; We cannot use parse-colon-path (files.el), since it kills
  ;; "//" entries using file-name-as-directory.
  ;; Similar: TeX-split-string, and RHOGEE's psg-list-env
  ;; in ff-paths and bib-cite.  The EMPTY arg may help mimic kpathsea.
  (if (or empty (getenv env))		; should return something
      (let ((start 0) match dir ret)
	(setq env (concat (getenv env) path-separator))
	(while (setq match (string-match path-separator env start))
	  (setq dir (substring env start match) start (1+ match))
	  ;;(and (file-directory-p dir) (not (member dir ret)) ...)
	  (setq ret (cons dir ret)))
	(setq ret (nreverse ret))
	(and empty (setq match (member "" ret))
	     (progn			; allow string or list here
	       (setcdr match (append (cdr-safe empty) (cdr match)))
	       (setcar match (or (car-safe empty) empty))))
	ret)))

(defun ffap-reduce-path (path)
  "Remove duplicates and non-directories from PATH list."
  (let (ret tem)
    (while path
      (setq tem path path (cdr path))
      (if (equal (car tem) ".") (setcar tem ""))
      (or (member (car tem) ret)
	  (not (file-directory-p (car tem)))
	  (progn (setcdr tem ret) (setq ret tem))))
    (nreverse ret)))

(defun ffap-all-subdirs (dir &optional depth)
  "Return list of all subdirectories under DIR, starting with itself.
Directories beginning with \".\" are ignored, and directory symlinks
are listed but never searched (to avoid loops).
Optional DEPTH limits search depth."
  (and (file-exists-p dir)
       (ffap-all-subdirs-loop (expand-file-name dir) (or depth -1))))

(defun ffap-all-subdirs-loop (dir depth) ; internal
  (setq depth (1- depth))
  (cons dir
	(and (not (eq depth -1))
             (apply #'nconc
		    (mapcar
                     (lambda (d)
                       (cond
                        ((not (file-directory-p d)) nil)
                        ((file-symlink-p d) (list d))
                        (t (ffap-all-subdirs-loop d depth))))
		     (directory-files dir t "\\`[^.]")
		     )))))

(defvar ffap-kpathsea-depth 1
  "Bound on depth of subdirectory search in `ffap-kpathsea-expand-path'.
Set to 0 to avoid all searching, or nil for no limit.")

(defun ffap-kpathsea-expand-path (path)
  "Replace each \"//\"-suffixed dir in PATH by a list of its subdirs.
The subdirs begin with the original directory, and the depth of the
search is bounded by `ffap-kpathsea-depth'.  This is intended to mimic
kpathsea, a library used by some versions of TeX."
  (apply #'nconc
	 (mapcar
          (lambda (dir)
            (if (string-match "[^/]//\\'" dir)
                (ffap-all-subdirs (substring dir 0 -2) ffap-kpathsea-depth)
              (list dir)))
	  path)))

(defun ffap-locate-file (file nosuffix path)
  ;; The current version of locate-library could almost replace this,
  ;; except it does not let us override the suffix list.  The
  ;; compression-suffixes search moved to ffap-file-exists-string.
  "A generic path-searching function.
Returns the name of file in PATH, or nil.
Optional NOSUFFIX, if nil or t, is like the fourth argument
for `load': whether to try the suffixes (\".elc\" \".el\" \"\").
If a nonempty list, it is a list of suffixes to try instead.
PATH is a list of directories.

This uses `ffap-file-exists-string', which may try adding suffixes from
`ffap-compression-suffixes'."
  (if (file-name-absolute-p file)
      (setq path (list (file-name-directory file))
	    file (file-name-nondirectory file)))
  (let ((dir-ok (equal "" (file-name-nondirectory file)))
        (suffixes-to-try
	 (cond
	  ((consp nosuffix) nosuffix)
	  (nosuffix '(""))
	  (t '(".elc" ".el" ""))))
	suffixes try found)
    (while path
      (setq suffixes suffixes-to-try)
      (while suffixes
	(setq try (ffap-file-exists-string
		   (expand-file-name
		    (concat file (car suffixes)) (car path))))
	(if (and try (or dir-ok (not (file-directory-p try))))
	    (setq found try suffixes nil path nil)
	  (setq suffixes (cdr suffixes))))
      (setq path (cdr path)))
    found))

\f
;;; Action List (`ffap-alist'):
;;
;; These search actions depend on the major-mode or regexps matching
;; the current name.  The little functions and their variables are
;; deferred to the next section, at some loss of "code locality".

(defvar ffap-alist
  '(
    ("" . ffap-completable)		; completion, slow on some systems
    ("" . ffap-in-project)		; maybe in the root of the project
    ("\\.info\\'" . ffap-info)		; gzip.info
    ("\\`info/" . ffap-info-2)		; info/emacs
    ("\\`[-[:lower:]]+\\'" . ffap-info-3) ; (emacs)Top [only in the parentheses]
    ("\\.elc?\\'" . ffap-el)		; simple.el, simple.elc
    (emacs-lisp-mode . ffap-el-mode)	; rmail, gnus, simple, custom
    ;; (lisp-interaction-mode . ffap-el-mode) ; maybe
    (finder-mode . ffap-el-mode)	; type `C-h p' and try it
    (help-mode . ffap-el-mode)		; maybe useful
    (c++-mode . ffap-c++-mode)         ; search ffap-c++-path
    (cc-mode . ffap-c-mode)		; same
    ("\\.\\([chCH]\\|cc\\|hh\\)\\'" . ffap-c-mode) ; stdio.h
    (fortran-mode . ffap-fortran-mode)
    ("\\.[fF]\\'" . ffap-fortran-mode)
    (plain-tex-mode . ffap-tex-mode)    ; search ffap-tex-path
    (latex-mode . ffap-latex-mode)	; similar
    (plain-TeX-mode . ffap-tex-mode)    ; AUCTeX v14 counterpart
    (LaTeX-mode . ffap-latex-mode)      ; ditto
    ("\\.\\(tex\\|sty\\|doc\\|cls\\)\\'" . ffap-tex)
    ("\\.bib\\'" . ffap-bib)		; search ffap-bib-path
    ("\\`\\." . ffap-home)		; .emacs, .bashrc, .profile
    ;; This used to have a blank, but ffap-string-at-point doesn't
    ;; handle blanks.
    ;; https://lists.gnu.org/r/emacs-devel/2008-01/msg01058.html
    ("\\`[Rr][Ff][Cc][-#]?\\([0-9]+\\)"	; no $
     . ffap-rfc)			; "100% RFC2100 compliant"
    (dired-mode . ffap-dired)		; maybe in a subdirectory
    )
  "Alist of (KEY . FUNCTION) pairs parsed by `ffap-file-at-point'.
If string NAME at point (maybe \"\") is not a file or URL, these pairs
specify actions to try creating such a string.  A pair matches if either
  KEY is a symbol, and it equals `major-mode', or
  KEY is a string, it should match NAME as a regexp.
On a match, (FUNCTION NAME) is called and should return a file, an
URL, or nil.  If nil, search the alist for further matches.
While calling FUNCTION, the match data is set according to KEY if KEY
is a string, so that FUNCTION can use `match-string' and friends
to extract substrings.")

(put 'ffap-alist 'risky-local-variable t)

;; Example `ffap-alist' modifications:
;;
;; (setq ffap-alist                   ; remove a feature in `ffap-alist'
;;	 (delete (assoc 'c-mode ffap-alist) ffap-alist))
;;
;; (setq ffap-alist                   ; add something to `ffap-alist'
;;	 (cons
;;	  (cons "^YSN[0-9]+$"
;;		(defun ffap-ysn (name)
;;		  (concat
;;		   "http://www.physics.uiuc.edu/"
;;                 "ysn/httpd/htdocs/ysnarchive/issuefiles/"
;;		   (substring name 3) ".html")))
;;	  ffap-alist))

\f
;;; Action Definitions:
;;
;; Define various default members of `ffap-alist'.

(defun ffap-completable (name)
  (let* ((dir (or (file-name-directory name) default-directory))
	 (cmp (file-name-completion (file-name-nondirectory name) dir)))
    (and cmp (concat dir cmp))))

(declare-function project-root "project" (project))
(defun ffap-in-project (name)
  (when-let* ((project (project-current)))
    (file-name-concat (project-root project) name)))

(defun ffap-home (name) (ffap-locate-file name t '("~")))

(defun ffap-info (name)
  (ffap-locate-file
   name '("" ".info")
   (or (ffap-symbol-value 'Info-directory-list)
       (ffap-symbol-value 'Info-default-directory-list)
       )))

(defun ffap-info-2 (name) (ffap-info (substring name 5)))

(defun ffap-info-3 (name)
  ;; This ignores the node! "(emacs)Top" same as "(emacs)Intro"
  (and (equal (ffap-string-around) "()") (ffap-info name)))

(defun ffap-el (name) (ffap-locate-file name t load-path))

(defun ffap-el-mode (name)
  ;; If name == "foo.el" we will skip it, since ffap-el already
  ;; searched for it once.  (This assumes the default ffap-alist.)
  (and (not (string-match "\\.el\\'" name))
       (ffap-locate-file name '(".el") load-path)))

;; FIXME this duplicates the logic of Man-header-file-path.
;; There should be a single central variable or function for this.
;; See also (bug#10702):
;; cc-search-directories, semantic-c-dependency-system-include-path,
;; semantic-gcc-setup
(defvar ffap-c-path
  (let ((arch (with-temp-buffer
                (when (eq 0 (ignore-errors
                              (call-process "gcc" nil '(t nil) nil
                                            "-print-multiarch")))
                  (goto-char (point-min))
                  (buffer-substring (point) (line-end-position)))))
        (base '("/usr/include" "/usr/local/include")))
    (if (zerop (length arch))
        base
      (append base (list (expand-file-name arch "/usr/include")))))
  "List of directories to search for include files.")

(defun ffap-c-mode (name)
  (ffap-locate-file name t ffap-c-path))

(defvar ffap-c++-path
  (let ((c++-include-dir (with-temp-buffer
                           (when (eq 0 (ignore-errors
                                         (call-process "g++" nil t nil "-v")))
                             (goto-char (point-min))
                             (if (re-search-forward "--with-gxx-include-dir=\
\\([^[:space:]]+\\)"
                                                      nil 'noerror)
                                 (match-string 1)
                               (when (re-search-forward "gcc version \
\\([[:digit:]]+.[[:digit:]]+.[[:digit:]]+\\)"
                                                   nil 'noerror)
                                 (expand-file-name (match-string 1)
                                                   "/usr/include/c++/")))))))
    (if c++-include-dir
        (cons c++-include-dir ffap-c-path)
      ffap-c-path))
  "List of directories to search for include files.")

(defun ffap-c++-mode (name)
  (ffap-locate-file name t ffap-c++-path))

(defvar ffap-fortran-path '("../include" "/usr/include"))

(defun ffap-fortran-mode (name)
  (ffap-locate-file name t ffap-fortran-path))

(defvar ffap-tex-path
  t				; delayed initialization
  "Path where `ffap-tex-mode' looks for TeX files.
If t, `ffap-tex-init' will initialize this when needed.")

(defvar ffap-latex-guess-rules '(("" . ".sty")
                               ("" . ".cls")
                               ("" . ".ltx")
                               ("" . ".tex")
                               ("" . "") ;; in some rare cases the
                                         ;; extension is already in
                                         ;; the buffer.
                               ("beamertheme" . ".sty")
                               ("beamercolortheme". ".sty")
                               ("beamerfonttheme". ".sty")
                               ("beamerinnertheme". ".sty")
                               ("beameroutertheme". ".sty")
                               ("" . ".ldf"))
  "List of rules for guessing a filename.
Each rule is a cons (PREFIX . SUFFIX) used for guessing a
filename from the word at point by prepending PREFIX and
appending SUFFIX.")

(defun ffap-tex-init ()
  ;; Compute ffap-tex-path if it is now t.
  (and (eq t ffap-tex-path)
       ;; this may be slow, so say something
       (message "Initializing ffap-tex-path ...")
       (setq ffap-tex-path
	     (ffap-reduce-path
	      (cons
	       "."
	       (ffap-kpathsea-expand-path
		(append
		 (ffap-list-env "TEXINPUTS")
		 ;; (ffap-list-env "BIBINPUTS")
		 (ffap-symbol-value
		  'TeX-macro-global	; AUCTeX
		  '("/usr/local/lib/tex/macros"
		    "/usr/local/lib/tex/inputs")))))))))

(defun ffap-tex-mode (name)
  (ffap-tex-init)
  (ffap-locate-file name '(".tex" "") ffap-tex-path))

(defun ffap-latex-mode (name)
  "`ffap' function suitable for latex buffers.
This uses the program kpsewhich if available.  In this case, the
variable `ffap-latex-guess-rules' is used for building a filename
out of NAME."
  (cond ((file-exists-p name)
         name)
        ((not (executable-find "kpsewhich"))
         (ffap-tex-init)
         (ffap-locate-file name '(".cls" ".sty" ".tex" "") ffap-tex-path))
        (t
         (let ((curbuf (current-buffer))
               (guess-rules ffap-latex-guess-rules)
               (preferred-suffix-rules '(("input" . ".tex")
                                         ("include" . ".tex")
                                         ("usepackage" . ".sty")
                                         ("RequirePackageWithOptions" . ".sty")
                                         ("RequirePackage" . ".sty")
                                         ("documentclass" . ".cls")
                                         ("documentstyle" . ".cls")
                                         ("LoadClass" . ".cls")
                                         ("LoadClassWithOptions" . ".cls")
                                         ("bibliography" . ".bib")
                                         ("addbibresource" . ""))))
           ;; We now add preferred suffix in front of suffixes.
           (when
               ;; The condition is essentially:
               ;; (assoc (TeX-current-macro)
               ;;        (mapcar 'car preferred-suffix-rules))
               ;; but (TeX-current-macro) can take time, so we just
               ;; check if one of the `car' in preferred-suffix-rules
               ;; is found before point on the current line.  It
               ;; should cover most cases.
               (save-excursion
                 (re-search-backward (regexp-opt
                                      (mapcar 'car preferred-suffix-rules))
                                     (line-beginning-position)
                                     t))
             (push (cons "" (cdr (assoc (match-string 0) ; i.e. "(TeX-current-macro)"
                                        preferred-suffix-rules)))
                   guess-rules))
           (with-temp-buffer
             (let ((process-environment (buffer-local-value
                                         'process-environment curbuf))
                   (exec-path (buffer-local-value 'exec-path curbuf)))
               (apply #'call-process "kpsewhich" nil t nil
                      (mapcar (lambda (rule)
                                          (concat (car rule) name (cdr rule)))
                                        guess-rules)))
             (when (< (point-min) (point-max))
               (buffer-substring (goto-char (point-min)) (line-end-position))))))))

(defun ffap-tex (name)
  (ffap-tex-init)
  (ffap-locate-file name t ffap-tex-path))

(defvar ffap-bib-path
  (ffap-list-env "BIBINPUTS"
		 (ffap-reduce-path
		  '(
		    ;; a few wild guesses, need better
		    "/usr/local/lib/tex/macros/bib" ; Solaris?
		    "/usr/lib/texmf/bibtex/bib"	; Linux?
		    ))))

(defun ffap-bib (name)
  (ffap-locate-file name t ffap-bib-path))

(defun ffap-dired (name)
  (let ((pt (point)) try)
    (save-excursion
      (and (progn
	     (beginning-of-line)
	     (looking-at " *[-d]r[-w][-x][-r][-w][-x][-r][-w][-x] "))
	   (re-search-backward "^ *$" nil t)
	   (re-search-forward "^ *\\([^ \t\n:]*\\):\n *total " pt t)
	   (file-exists-p
	    (setq try
		  (expand-file-name
		   name
		   (buffer-substring
		    (match-beginning 1) (match-end 1)))))
	   try))))

(defun ffap-lcd (name)
  (declare (obsolete nil "29.1"))
  (and
   (or
    ;; lisp-dir-apropos output buffer:
    (string-match "Lisp Code Dir" (buffer-name))
    ;; Inside an LCD entry like |~/misc/ffap.el.Z|,
    ;; or maybe the holy LCD-Datafile itself:
    (member (ffap-string-around) '("||" "|\n")))
   (concat
    ;; lispdir.el may not be loaded yet:
    (ffap-host-to-filename
     (ffap-symbol-value 'elisp-archive-host
                        "archive.cis.ohio-state.edu"))
    (file-name-as-directory
     (ffap-symbol-value 'elisp-archive-directory
                        "/pub/gnu/emacs/elisp-archive/"))
    (substring name 2))))

(defcustom ffap-rfc-path "https://www.rfc-editor.org/in-notes/rfc%s.txt"
  "A `format' string making a filename for RFC documents.
This can be an URL, an ange-ftp or Tramp remote filename to
download, or a local filename if you have the full set of RFCs
locally.  See also `ffap-rfc-directories'."
  :type 'string
  :version "28.1")

(defcustom ffap-rfc-directories nil
  "A list of directories to look for RFC files.
If a given RFC isn't in these then `ffap-rfc-path' is offered."
  :type '(repeat directory)
  :version "23.1")

(defun ffap-rfc (name)
  (let ((num (match-string 1 name)))
    (or (ffap-locate-file (format "rfc%s.txt" num) t ffap-rfc-directories)
        (format ffap-rfc-path num))))

\f
;;; At-Point Functions:

(defvar ffap-string-at-point-mode-alist
  '(
    ;; The default, used when the `major-mode' is not found.
    ;; Slightly controversial decisions:
    ;; * strip trailing "@", ":" and enclosing "{"/"}".
    ;; * no commas (good for latex)
    (file "--:\\\\${}+<>@-Z_[:alpha:]~*?#" "{<@" "@>;.,!:}")
    ;; An url, or maybe an email/news message-id:
    (url "--:=&?$+@-Z_[:alpha:]~#,%;*()!'" "^[0-9a-zA-Z]" ":;.,!?")
    ;; Find a string that does *not* contain a colon:
    (nocolon "--9$+<>@-Z_[:alpha:]~" "<@" "@>;.,!?")
    ;; A machine:
    (machine "-[:alnum:]." "" ".")
    ;; Mathematica paths: allow backquotes
    (math-mode ",-:$+<>@-Z_[:lower:]~`" "<" "@>;.,!?`:")
    ;; (La)TeX: don't allow braces
    (latex-mode "--:\\\\$+<>@-Z_[:alpha:]~*?" "<@" "@>;.,!:")
    (plain-tex-mode "--:\\\\$+<>@-Z_[:alpha:]~*?" "<@" "@>;.,!:")
    ;; AUCTeX v14 counterparts:
    (LaTeX-mode "--:\\\\$+<>@-Z_[:alpha:]~*?" "<@" "@>;.,!:")
    (plain-TeX-mode "--:\\\\$+<>@-Z_[:alpha:]~*?" "<@" "@>;.,!:")
    ;; XML: don't allow angle brackets
    (xml-mode "--:\\\\${}+@-Z_[:alpha:]~*?#" "{<@" "@>;.,!:}")
    (nxml-mode "--:\\\\${}+@-Z_[:alpha:]~*?#" "{<@" "@>;.,!:}")
    )
  "Alist of (MODE CHARS BEG END), where MODE is a symbol.
This is possibly a major-mode name, or one of the symbols
`file', `url', `machine', and `nocolon'.
Function `ffap-string-at-point' uses the data fields as follows:
1. find a maximal string of CHARS around point,
2. strip BEG chars before point from the beginning,
3. strip END chars after point from the end.
The arguments CHARS, BEG and END are handled as described in
`skip-chars-forward'.")

(defvar ffap-string-at-point nil            ; for ff-paths
  "Last string returned by the function `ffap-string-at-point'.")

(defcustom ffap-file-name-with-spaces nil
  "If non-nil, enable looking for paths with spaces in `ffap-string-at-point'.
Enabling this variable may lead to `find-file-at-point' guessing
wrong more often when trying to find a file name intermingled
with normal text, but can be useful when working on systems that
normally use spaces in file names (like Microsoft Windows and the
like)."
  :type 'boolean
  :version "28.1")

(defun ffap-search-backward-file-end (&optional dir-separator end)
  "Search backward position point where file would probably end.
Optional DIR-SEPARATOR defaults to \"/\".  The search maximum is
`line-end-position' or optional END point.

Suppose the cursor is somewhere that might be near end of file,
the guessing would position point before punctuation (like comma)
after the file extension:

  C:\\temp\\file.log, which contain ....
  =============================== (before)
  ---------------- (after)


  C:\\temp\\file.log on Windows or /tmp/file.log on Unix
  =============================== (before)
  ---------------- (after)

The strategy is to search backward until DIR-SEPARATOR which defaults to
\"/\" and then take educated guesses.

Move point and return point if an adjustment was done."
  (unless dir-separator
    (setq dir-separator "/"))
  (let ((opoint (point))
	point punct whitespace-p)
    (when (re-search-backward
	   (regexp-quote dir-separator) (line-beginning-position) t)
      ;; Move to the beginning of the match..
      (forward-char 1)
      ;; ... until typical punctuation.
      (when (re-search-forward "\\([][<>()\"'`,.:;]\\)"
			       (or end
				   (line-end-position))
			       t)
	(setq end (match-end 0))
	(setq punct (match-string 1))
	(setq whitespace-p (looking-at "[ \t\r\n]\\|$"))
	(goto-char end)
	(cond
	 ((and (string-equal punct ".")
	       whitespace-p)            ;end of sentence
	  (setq point (1- (point))))
	 ((and (string-equal punct ".")
	       (looking-at "[a-zA-Z0-9.]+")) ;possibly file extension
	  (setq point (match-end 0)))
	 (t
	  (setq point (point)))))
      (goto-char opoint)
      (when point
	(goto-char point)
	point))))

(defun ffap-search-forward-file-end (&optional dir-separator)
  "Search DIR-SEPARATOR and position point at file's maximum ending.
This includes spaces.
Optional DIR-SEPARATOR defaults to \"/\".
Call `ffap-search-backward-file-end' to refine the ending point."
  (unless dir-separator
    (setq dir-separator "/"))
  (let* ((chars                         ;expected chars in file name
	  (concat "[^][^<>()\"'`;,#*|"
		  ;; exclude the opposite as we know the separator
		  (if (string-equal dir-separator "/")
		      "\\\\"
		    "/")
		  "\t\r\n]"))
	 (re (concat
	      chars "*"
	      (if dir-separator
		  (regexp-quote dir-separator)
		"/")
	      chars "*")))
    (when (looking-at re)
      (goto-char (match-end 0)))))

(defun ffap-dir-separator-near-point ()
  "Search backward and forward for closest slash or backlash in line.
Return string slash or backslash.  Point is moved to closest position."
  (let ((point (point))
	str pos)
    (when (looking-at ".*?/")
      (setq str "/"
	    pos (match-end 0)))
    (when (and (looking-at ".*?\\\\")
               (or (null pos)
	           (< (match-end 0) pos)))
      (setq str "\\"
	    pos (match-end 0)))
    (goto-char point)
    (when (and (re-search-backward "/" (line-beginning-position) t)
               (or (null pos)
	           (< (- point (point)) (- pos point))))
      (setq str "/"
	    pos (1+ (point)))) ;1+ to keep cursor at the end of char
    (goto-char point)
    (when (and (re-search-backward "\\\\" (line-beginning-position) t)
               (or (null pos)
		   (< (- point (point)) (- pos point))))
      (setq str "\\"
	    pos (1+ (point))))
    (when pos
      (goto-char pos))
    str))

(defun ffap-string-at-point (&optional mode)
  "Return a string of characters from around point.

MODE (defaults to value of `major-mode') is a symbol used to look up
string syntax parameters in `ffap-string-at-point-mode-alist'.

If MODE is not found, we use `file' instead of MODE.

If the region is active, return a string from the region.

If the point is in a comment, ensure that the returned string does not
contain the comment start characters (especially for major modes that
have \"//\" as comment start characters).

Set the variables `ffap-string-at-point' and
`ffap-string-at-point-region'.

When the region is active and larger than `ffap-max-region-length',
return an empty string, and set `ffap-string-at-point-region' to `(1 1)'."
  (let* (dir-separator
         (args
	  (cdr
	   (or (assq (or mode major-mode) ffap-string-at-point-mode-alist)
	       (assq 'file ffap-string-at-point-mode-alist))))
         (region-selected (use-region-p))
	 (pt (point))
         (beg (if region-selected
		  (region-beginning)
		(save-excursion
	          (if (and ffap-file-name-with-spaces
			   (memq mode '(nil file)))
		      (when (setq dir-separator (ffap-dir-separator-near-point))
		        (while (re-search-backward
			        (regexp-quote dir-separator)
			        (line-beginning-position) t)
		          (goto-char (match-beginning 0))))
		    (skip-chars-backward (car args))
		    (skip-chars-forward (nth 1 args) pt))
		  (point))))
         (end (if region-selected
		  (region-end)
		(save-excursion
		  (skip-chars-forward (car args))
		  (skip-chars-backward (nth 2 args) pt)
	          (when (and ffap-file-name-with-spaces
			     (memq mode '(nil file)))
		    (ffap-search-forward-file-end dir-separator)
		    (ffap-search-backward-file-end dir-separator))
		  (point))))
         (region-len (- (max beg end) (min beg end))))

    ;; If the initial characters of the to-be-returned string are the
    ;; current major mode's comment starter characters, *and* are
    ;; not part of a comment, remove those from the returned string
    ;; (Bug#24057).
    ;; Example comments in `c-mode' (which considers lines beginning
    ;; with "//" as comments):
    ;;  //tmp - This is a comment. It does not contain any path reference.
    ;;  ///tmp - This is a comment. The "/tmp" portion in that is a path.
    ;;  ////tmp - This is a comment. The "//tmp" portion in that is a path.
    (when (and
           ;; Proceed if no region is selected by the user.
           (null region-selected)
           ;; Check if END character is part of a comment.
           (save-excursion
             (nth 4 (syntax-ppss end))))
      ;; Move BEG to beginning of comment (after the comment start
      ;; characters), or END, whichever comes first.
      (save-excursion
        (let ((state (syntax-ppss beg)))
          ;; (nth 4 (syntax-ppss)) will be nil for comment start chars.
          (unless (nth 4 state)
            (parse-partial-sexp beg end nil nil state :commentstop)
            (setq beg (point))))))

    (if (and (natnump ffap-max-region-length)
             (< region-len ffap-max-region-length)) ; Bug#25243.
        (setf ffap-string-at-point-region (list beg end)
              ffap-string-at-point
              (buffer-substring-no-properties beg end))
      (setf ffap-string-at-point-region (list 1 1)
            ffap-string-at-point ""))))

(defun ffap-string-around ()
  ;; Sometimes useful to decide how to treat a string.
  "Return string of two chars around last result of function
`ffap-string-at-point'.
Assumes the buffer has not changed."
  (save-excursion
    (format "%c%c"
	    (progn
	      (goto-char (car ffap-string-at-point-region))
	      (preceding-char))		; maybe 0
	    (progn
	      (goto-char (nth 1 ffap-string-at-point-region))
	      (following-char))		; maybe 0
	    )))

(defun ffap-copy-string-as-kill (&optional mode)
  ;; Requested by MCOOK.  Useful?
  "Call function `ffap-string-at-point', and copy result to `kill-ring'."
  (interactive)
  (let ((str (ffap-string-at-point mode)))
    (if (equal "" str)
	(message "No string found around point.")
      (kill-new str)
      ;; Older: (apply 'copy-region-as-kill ffap-string-at-point-region)
      (message "Copied to kill ring: %s"  str))))

;;;###autoload
(defun ffap-url-at-point ()
  "Return URL from around point if it exists, or nil.

Sets the variable `ffap-string-at-point-region' to the bounds of URL, if any."
  (when ffap-url-regexp
    (let ((thing-at-point-beginning-of-url-regexp ffap-url-regexp)
          (thing-at-point-default-mail-uri-scheme ffap-foo-at-bar-prefix)
          val)
      (setq val (thing-at-point-url-at-point ffap-lax-url
                                             (if (use-region-p)
                                                 (cons (region-beginning)
                                                       (region-end)))))
      (if val
          (let ((bounds (thing-at-point-bounds-of-url-at-point
                         ffap-lax-url)))
            (setq ffap-string-at-point-region
                  (list (car bounds) (cdr bounds)))))
      val)))

(defvar ffap-gopher-regexp
  "\\<\\(Type\\|Name\\|Path\\|Host\\|Port\\) *= *"
  "Regexp matching a key in a gopher bookmark.
Set to nil to disable matching gopher bookmarks.")

(defun ffap--gopher-var-on-line ()
  "Return (KEY . VALUE) of gopher bookmark on current line."
  (save-excursion
    (end-of-line)
    (skip-chars-backward " ")
    (let ((eol (point)))
      (beginning-of-line)
      (when (re-search-forward ffap-gopher-regexp eol t)
        (let ((key (match-string 1))
              (val (buffer-substring-no-properties (match-end 0) eol)))
          (cons (intern (downcase key)) val))))))

(defun ffap-gopher-at-point ()
  "If point is inside a gopher bookmark block, return its URL.

Sets the variable `ffap-string-at-point-region' to the bounds of URL, if any."
  ;; `gopher-parse-bookmark' from gopher.el is not so robust
  (when (stringp ffap-gopher-regexp)
    (save-excursion
      (let* ((beg (progn (beginning-of-line)
                         (while (and (not (bobp)) (ffap--gopher-var-on-line))
                           (forward-line -1))
                         (point)))
             (bookmark (cl-loop for keyval = (ffap--gopher-var-on-line)
                                while keyval collect keyval
                                do (forward-line 1)
                                until (eobp))))
        (when bookmark
          (setq ffap-string-at-point-region (list beg (point)))
          (let-alist (nconc bookmark '((type . "1") (port . "70")))
            (if (and .path (string-match "\\`ftp:.*@" .path))
                (concat "ftp://"
                        (substring .path 4 (1- (match-end 0)))
                        (substring .path (match-end 0)))
              (and (= (length .type) 1)
                   .host ;; (ffap-machine-p host)
                   (concat "gopher://" .host
                           (if (equal .port "70") "" (concat ":" .port))
                           "/" .type .path)))))))))

(defvar ffap-ftp-sans-slash-regexp
  (and
   ffap-ftp-regexp
   ;; Note: by now, we know it is not an url.
   ;; Icky regexp avoids: default: 123: foo::bar cs:pub
   ;; It does match on: mic@cs: cs:/pub mathcs.emory.edu: (point at end)
   "\\`\\([^:@]+@[^:@]+:\\|[^@.:]+\\.[^@:]+:\\|[^:]+:[~/]\\)\\([^:]\\|\\'\\)")
  "Strings matching this are coerced to FTP file names by ffap.
That is, ffap just prepends \"/\".  Set to nil to disable.")

(defun ffap-file-at-point ()
  "Return filename from around point if it exists, or nil.
Existence test is skipped for names that look remote.
If the filename is not obvious, it also tries `ffap-alist',
which may actually result in an URL rather than a filename."
  ;; Note: this function does not need to look for url's, just
  ;; filenames.  On the other hand, it is responsible for converting
  ;; a pseudo-url "site.com://dir" to an ftp file name
  (let* ((case-fold-search t)		; url prefixes are case-insensitive
	 (data (match-data))
	 (string (ffap-string-at-point)) ; uses mode alist
	 (name
	  (or (condition-case nil
		  (and (not (string-search "//" string)) ; foo.com://bar
		       (substitute-in-file-name string))
		(error nil))
	      string))
	 (abs (file-name-absolute-p name))
	 (default-directory default-directory)
         (oname name))
    (unwind-protect
	(cond
	 ;; Immediate rejects (/ and // and /* are too common in C/C++):
         ((member name '("" "/" "//" "/*" ".")) nil)
         ;; Immediately test local filenames.  If default-directory is
         ;; remote, you probably already have a connection.
         ((and (not abs) (ffap-file-exists-string name)))
         ;; Try stripping off line numbers; good for compilation/grep output.
         ((and (not abs) (string-match ":[0-9]" name)
               (ffap-file-exists-string (substring name 0 (match-beginning 0)))))
         ;; Try stripping off prominent (non-root - #) shell prompts
	 ;; if the ffap-shell-prompt-regexp is non-nil.
         ((and ffap-shell-prompt-regexp
	       (not abs) (string-match ffap-shell-prompt-regexp name)
               (ffap-file-exists-string (substring name (match-end 0)))))
	 ;; Accept remote names without actual checking (too slow):
	 ((and abs (ffap-file-remote-p name)))
	 ;; Ok, not remote, try the existence test even if it is absolute:
	 ((and abs (ffap-file-exists-string name)))
	 ;; Try stripping off line numbers.
	 ((and abs (string-match ":[0-9]" name)
	       (ffap-file-exists-string (substring name 0 (match-beginning 0)))))
	 ;; If it contains a colon, get rid of it (and return if exists)
	 ((and (string-match path-separator name)
	       (let ((this-name (ffap-string-at-point 'nocolon)))
                 ;; But don't interpret the first part if ":/bin" as
                 ;; the empty string.
	         (when (> (length this-name) 0)
                   (setq name this-name)
	           (ffap-file-exists-string name)))))
         ;; File does not exist, try the alist:
	 ((let ((alist ffap-alist) tem try case-fold-search)
	    (while (and alist (not try))
	      (setq tem (car alist) alist (cdr alist))
	      (if (or (eq major-mode (car tem))
		      (and (stringp (car tem))
			   (string-match (car tem) name)))
		  (and (setq try
			     (condition-case nil
				 (funcall (cdr tem) name)
			       (error nil)))
		       (setq try (or
				  (ffap-url-p try) ; not a file!
				  (ffap-file-remote-p try)
				  (ffap-file-exists-string try))))))
	    try))
         ;; Try adding a leading "/" (common omission in ftp file names).
         ;; Note that this uses oname, which still has any colon part.
         ;; This should have a lower priority than the alist stuff,
         ;; else it matches things like "ffap.el:1234:56:Warning".
         ((and (not abs)
               ffap-ftp-sans-slash-regexp
               (string-match ffap-ftp-sans-slash-regexp oname)
               (ffap-file-remote-p (concat "/" oname))))
	 ;; Alist failed?  Try to guess an active remote connection
	 ;; from buffer variables, and try once more, both as an
	 ;; absolute and relative file name on that remote host.
	 ((let* (ffap-rfs-regexp	; suppress
		 (remote-dir
		  (cond
		   ((ffap-file-remote-p default-directory))
		   ((and (eq major-mode 'internal-ange-ftp-mode)
			 (string-match "^\\*ftp \\(.*\\)@\\(.*\\)\\*$"
				       (buffer-name)))
                    (concat "/" (substring (buffer-name) 5 -1) ":")))))
	    (and remote-dir
		 (or
		  (and (string-match "\\`\\(/?~?ftp\\)/" name)
		       (ffap-file-exists-string
			(ffap-replace-file-component
			 remote-dir (substring name (match-end 1)))))
		  (ffap-file-exists-string
		   (ffap-replace-file-component remote-dir name))))))
	 ((and ffap-dired-wildcards
	       (string-match ffap-dired-wildcards name)
	       abs
	       (ffap-file-exists-string (file-name-directory
					 (directory-file-name name)))
	       name))
         ;; Try all parent directories by deleting the trailing directory
         ;; name until existing directory is found or name stops changing
         ((let ((dir name))
            (while (and dir
                        (not (ffap-file-exists-string dir))
                        (not (equal dir (setq dir (file-name-directory
                                                   (directory-file-name dir)))))))
            (and (not (string= dir "/"))
		 (ffap-file-exists-string dir))))
	 )
      (set-match-data data))))
\f
;;; Prompting (`ffap-read-file-or-url'):
;;
;; We want to complete filenames as in read-file-name, but also url's
;; which read-file-name-internal would truncate at the "//" string.
;; The solution here is to forcefully activate url-handler-mode, which
;; takes care of it for us.

(defun ffap--url-file-handler (operation &rest args)
  (let ((inhibit-file-name-handlers
         (cons 'ffap--url-file-handler inhibit-file-name-handlers))
        (inhibit-file-name-operation operation))
    (cl-case operation
      ;; We mainly just want to disable these bits:
      (substitute-in-file-name (car args))
      (expand-file-name (car args))
      (unhandled-file-name-directory temporary-file-directory)
      (otherwise
       (apply operation args)))))

(defun ffap-read-file-or-url (prompt guess)
  "Read file or URL from minibuffer, with PROMPT and initial GUESS."
  (let ((elem (cons ffap-url-regexp #'ffap--url-file-handler)))
    (unwind-protect
        (progn
          (push elem file-name-handler-alist)
          (if (ffap-url-p guess)
              ;; We're using the default file name prompter here -- it
              ;; allows you to switch back to reading a file name,
              ;; while other prompters, like ido, really expect a
              ;; file, and don't allow you to edit it if it's an URL.
              (funcall #'read-file-name-default prompt guess guess)
            (unless guess
              (setq guess default-directory))
            (unless (ffap-file-remote-p guess)
              (setq guess (abbreviate-file-name (expand-file-name guess))))
            (read-file-name prompt
                            (file-name-directory guess) nil nil
                            (file-name-nondirectory guess))))
      ;; Remove the special handler manually.  We used to just let-bind
      ;; file-name-handler-alist to preserve its value, but that caused
      ;; other modifications to be lost (e.g. when Tramp gets loaded
      ;; during the completing-read call).
      (setq file-name-handler-alist (delq elem file-name-handler-alist)))))

\f
;;; Highlighting (`ffap-highlight'):

(defvar ffap-highlight t
  "If non-nil, ffap highlights the current buffer substring.")

(defface ffap
  '((t :inherit highlight))
  "Face used to highlight the current buffer substring."
  :group 'ffap
  :version "22.1")

(defvar ffap-highlight-overlay nil
  "Overlay used by function `ffap-highlight'.")

(defun ffap-highlight (&optional remove)
  "If `ffap-highlight' is set, highlight the guess in this buffer.
That is, the last buffer substring found by `ffap-string-at-point'.
Optional argument REMOVE means to remove any such highlighting.
Uses the face `ffap' if it is defined, or else `highlight'."
  (cond
   (remove
    (and ffap-highlight-overlay
	 (delete-overlay ffap-highlight-overlay))
    )
   ((not ffap-highlight) nil)
   (ffap-highlight-overlay
    (move-overlay
     ffap-highlight-overlay
     (car ffap-string-at-point-region)
     (nth 1 ffap-string-at-point-region)
     (current-buffer)))
   (t
    (setq ffap-highlight-overlay
	  (apply 'make-overlay ffap-string-at-point-region))
    (overlay-put ffap-highlight-overlay 'face 'ffap))))

\f
;;; Main Entrance (`find-file-at-point' == `ffap'):

(defun ffap-guesser ()
  "Return file or URL or nil, guessed from text around point."
  (or (and ffap-url-regexp
	   (ffap-fixup-url (or (ffap-url-at-point)
			       (ffap-gopher-at-point))))
      (ffap-file-at-point)		; may yield url!
      (ffap-fixup-email (thing-at-point 'email))
      (ffap-fixup-machine (ffap-machine-at-point))))

(defun ffap-prompter (&optional guess suffix)
  ;; Does guess and prompt step for find-file-at-point.
  ;; Extra complication for the temporary highlighting.
  (unwind-protect
      ;; This catch will let ffap-alist entries do their own prompting
      ;; and then maybe skip over this prompt (ff-paths, for example).
      (catch 'ffap-prompter
	(ffap-read-file-or-url
	 (if ffap-url-regexp
             (format "Find file or URL%s: " (or suffix ""))
           (format "Find file%s: " (or suffix "")))
	 (prog1
             (let ((mark-active nil))
               ;; Don't use the region here, since it can be something
               ;; completely unwieldy.  If the user wants that, she could
               ;; use M-w before and then C-y.  --Stef
               (setq guess (or guess (ffap-guesser)))) ; using ffap-alist here
	   (and guess (ffap-highlight))
	   )))
    (ffap-highlight t)))

;;;###autoload
(defun find-file-at-point (&optional filename)
  "Find FILENAME, guessing a default from text around point.
If `ffap-url-regexp' is not nil, the FILENAME may also be an URL.
With a prefix, this command behaves exactly like `ffap-file-finder'.
If `ffap-require-prefix' is set, the prefix meaning is reversed.
See also the variables `ffap-dired-wildcards',
`ffap-url-unwrap-local', `ffap-url-unwrap-remote',
`ffap-file-name-with-spaces', and the functions `ffap-file-at-point'
and `ffap-url-at-point'."
  (interactive)
  (if (and (called-interactively-p 'interactive)
	   (if ffap-require-prefix (not current-prefix-arg)
	     current-prefix-arg))
      ;; Do exactly the ffap-file-finder command, even the prompting:
      (let (current-prefix-arg)		; we already interpreted it
	(call-interactively ffap-file-finder))
    (or filename (setq filename (ffap-prompter)))
    (let ((url (ffap-url-p filename)))
      (cond
       (url
	(let (current-prefix-arg)
	  (funcall ffap-url-fetcher url)))
       ((and ffap-pass-wildcards-to-dired
	     ffap-dired-wildcards
	     (string-match ffap-dired-wildcards filename))
	(funcall ffap-directory-finder filename))
       ((and ffap-dired-wildcards
	     (string-match ffap-dired-wildcards filename)
	     find-file-wildcards
	     ;; Check if it's find-file that supports wildcards arg
	     (memq ffap-file-finder '(find-file find-alternate-file)))
	(funcall ffap-file-finder (expand-file-name filename) t))
       ((or (not ffap-newfile-prompt)
	    (file-exists-p filename)
	    (y-or-n-p "File does not exist, create buffer? "))
	(funcall ffap-file-finder
                 ;; expand-file-name fixes "~/~/.emacs" bug
	         (expand-file-name filename)))
       ;; User does not want to find a non-existent file:
       ((signal 'file-missing (list "Opening file buffer"
				    "No such file or directory"
				    filename)))))))

;; Shortcut: allow `M-x ffap' rather than `M-x find-file-at-point'.
;;;###autoload
(defalias 'ffap 'find-file-at-point)

\f
;;; Menu support (`ffap-menu'):

(defcustom ffap-menu-regexp nil
  "If non-nil, regexp overriding `ffap-next-regexp' in `ffap-menu'.
Make this more restrictive for faster menu building.
For example, try \":/\" for URL (and some FTP) references."
  :type '(choice (const nil) regexp)
  :group 'ffap)

(defvar-local ffap-menu-alist nil
  "Buffer local cache of menu presented by `ffap-menu'.")

(defvar ffap-menu-text-plist
  (cond
   ((display-mouse-p) '(face bold mouse-face highlight)) ; keymap <mousy-map>
   (t nil))
  "Text properties applied to strings found by `ffap-menu-rescan'.
These properties may be used to fontify the menu references.")

;;;###autoload
(defun ffap-menu (&optional rescan)
  "Put up a menu of files and URLs mentioned in this buffer.
Then set mark, jump to choice, and try to fetch it.  The menu is
cached in `ffap-menu-alist', and rebuilt by `ffap-menu-rescan'.
The optional RESCAN argument (a prefix, interactively) forces
a rebuild.  Searches with `ffap-menu-regexp'."
  (interactive "P")
  ;; (require 'imenu) -- no longer used, but roughly emulated
  (if (or (not ffap-menu-alist) rescan
	  ;; or if the first entry is wrong:
	  (and ffap-menu-alist
	       (let ((first (car ffap-menu-alist)))
		 (save-excursion
		   (goto-char (cdr first))
		   (not (equal (car first) (ffap-guesser)))))))
      (ffap-menu-rescan))
  ;; Tail recursive:
  (ffap-menu-ask
   (if ffap-url-regexp "Find file or URL" "Find file")
   (cons (cons "*Rescan Buffer*" -1) ffap-menu-alist)
   'ffap-menu-cont))

(defun ffap-menu-cont (choice)		; continuation of ffap-menu
  (if (< (cdr choice) 0)
      (ffap-menu t)			; *Rescan*
    (push-mark)
    (goto-char (cdr choice))
    ;; Momentary highlight:
    (unwind-protect
	(progn
	  (and ffap-highlight (ffap-guesser) (ffap-highlight))
	  (sit-for 0)			; display
	  (find-file-at-point (car choice)))
      (ffap-highlight t))))

(defun ffap-menu-ask (title alist cont)
  "Prompt from a menu of choices, and then apply some action.
Arguments are TITLE, ALIST, and CONT (a continuation function).
This uses either a menu or the minibuffer depending on invocation.
The TITLE string is used as either the prompt or menu title.
Each ALIST entry looks like (STRING . DATA) and defines one choice.
Function CONT is applied to the entry chosen by the user."
  ;; Note: this function is used with a different continuation
  ;; by the ffap-url add-on package.
  ;; Could try rewriting to use easymenu.el.
  (let (choice)
    (cond
     ;; Emacs mouse:
     ((and (fboundp 'x-popup-menu)
           (listp last-nonmenu-event)
           last-nonmenu-event)
      (setq choice
	    (x-popup-menu
	     t
	     (list "" (cons title
			    (mapcar (lambda (i) (cons (car i) i))
				    alist))))))
     ;; minibuffer with completion buffer:
     (t
      (let ((minibuffer-setup-hook 'minibuffer-completion-help))
	;; Bug: prompting may assume unique strings, no "".
	(setq choice
	      (completing-read
	       (format-prompt title (car (car alist)))
	       alist nil t
	       ;; (cons (car (car alist)) 0)
	       nil)))
      (sit-for 0)			; redraw original screen
      ;; Convert string to its entry, or else the default:
      (setq choice (or (assoc choice alist) (car alist)))))
    (if choice
	(funcall cont choice)
      (message "No choice made!")	; possible with menus
      nil)))

(defun ffap-menu-rescan ()
  "Search buffer for `ffap-menu-regexp' to build `ffap-menu-alist'.
Applies `ffap-menu-text-plist' text properties at all matches."
  (interactive)
  (let ((ffap-next-regexp (or ffap-menu-regexp ffap-next-regexp))
	(range (- (point-max) (point-min)))
	(mod (buffer-modified-p))	; was buffer modified?
	;; inhibit-read-only works on read-only text properties
	;; as well as read-only buffers.
	(inhibit-read-only t)		; to set text-properties
	item
	;; Avoid repeated searches of the *mode-alist:
	(major-mode (if (assq major-mode ffap-string-at-point-mode-alist)
			major-mode
		      'file)))
    (setq ffap-menu-alist nil)
    (unwind-protect
	(save-excursion
	  (goto-char (point-min))
	  (while (setq item (ffap-next-guess))
	    (setq ffap-menu-alist (cons (cons item (point)) ffap-menu-alist))
	    (add-text-properties (car ffap-string-at-point-region) (point)
				 ffap-menu-text-plist)
	    (message "Scanning...%2d%% <%s>"
		     (floor (* 100.0 (- (point) (point-min))) range) item)))
      (or mod (restore-buffer-modified-p nil))))
  (message "Scanning...done")
  ;; Remove duplicates.
  (setq ffap-menu-alist			; sort by item
	(sort ffap-menu-alist
              (lambda (a b) (string-lessp (car a) (car b)))))
  (let ((ptr ffap-menu-alist))		; remove duplicates
    (while (cdr ptr)
      (if (equal (car (car ptr)) (car (car (cdr ptr))))
	  (setcdr ptr (cdr (cdr ptr)))
	(setq ptr (cdr ptr)))))
  (setq ffap-menu-alist			; sort by position
	(sort ffap-menu-alist
              (lambda (a b) (< (cdr a) (cdr b))))))

\f
;;; Mouse Support (`ffap-at-mouse'):
;;
;; See the suggested binding in `ffap-bindings' (near eof).

(defvar ffap-at-mouse-fallback nil	; ffap-menu? too time-consuming
  "Command invoked by `ffap-at-mouse' if nothing found at click, or nil.
Ignored when `ffap-at-mouse' is called programmatically.")
(put 'ffap-at-mouse-fallback 'risky-local-variable t)

;;;###autoload
(defun ffap-at-mouse (e)
  "Find file or URL guessed from text around mouse click.
Interactively, calls `ffap-at-mouse-fallback' if no guess is found.
Return value:
  * if a guess string is found, return it (after finding it)
  * if the fallback is called, return whatever it returns
  * otherwise, nil"
  (interactive "e")
  (let ((guess
	 ;; Maybe less surprising without the save-excursion?
	 (save-excursion
	   (mouse-set-point e)
	   ;; Would prefer to do nothing unless click was *on* text.  How
	   ;; to tell that the click was beyond the end of current line?
	   (ffap-guesser))))
    (cond
     (guess
      (set-buffer (window-buffer (car (event-start e))))
      (ffap-highlight)
      (unwind-protect
	  (progn
	    (sit-for 0)			; display
	    (message "Finding `%s'" guess)
	    (find-file-at-point guess)
	    guess)			; success: return non-nil
	(ffap-highlight t)))
     ((called-interactively-p 'interactive)
      (if ffap-at-mouse-fallback
	  (call-interactively ffap-at-mouse-fallback)
	(message "No file or URL found at mouse click.")
	nil))				; no fallback, return nil
     ;; failure: return nil
     )))

\f
;;; ffap-other-*, ffap-read-only-*, ffap-alternate-* commands:

;; There could be a real `ffap-noselect' function, but we would need
;; at least two new user variables.
;; So instead, we just fake it with a slow save-window-excursion.

(defun ffap-other-window (filename)
  "Like `ffap', but put buffer in another window.
Only intended for interactive use."
  (interactive (list (ffap-prompter nil " other window")))
  (pcase (save-window-excursion (find-file-at-point filename))
    ((or (and (pred bufferp) b) `(,(and (pred bufferp) b) . ,_))
     (switch-to-buffer-other-window b))))

(defun ffap-other-frame (filename)
  "Like `ffap', but put buffer in another frame.
Only intended for interactive use."
  (interactive (list (ffap-prompter nil " other frame")))
  ;; Extra code works around dedicated windows:
  (let* ((win (selected-window))
	 (wdp (window-dedicated-p win))
	 value)
    (unwind-protect
	(progn
	  (set-window-dedicated-p win nil)
	  (switch-to-buffer-other-frame
	   (save-window-excursion
	     (setq value (find-file-at-point filename))
	     (unless (or (bufferp value) (bufferp (car-safe value)))
	       (setq value (current-buffer)))
	     (current-buffer))))
      (set-window-dedicated-p win wdp))
    value))

(defun ffap-other-tab (filename)
  "Like `ffap', but put buffer in another tab.
Only intended for interactive use."
  (interactive (list (ffap-prompter nil " other tab")))
  (pcase (save-window-excursion (find-file-at-point filename))
    ((or (and (pred bufferp) b) `(,(and (pred bufferp) b) . ,_))
     (switch-to-buffer-other-tab b))))

(defun ffap--toggle-read-only (buffer-or-list)
  (dolist (buffer (if (listp buffer-or-list)
		      buffer-or-list
		    (list buffer-or-list)))
    (with-current-buffer buffer
      (read-only-mode 1))))

(defun ffap-read-only (filename)
  "Like `ffap', but mark buffer as read-only.
Only intended for interactive use."
  (interactive (list (ffap-prompter nil " read only")))
  (let ((value (find-file-at-point filename)))
    (unless (or (bufferp value) (bufferp (car-safe value)))
      (setq value (current-buffer)))
    (ffap--toggle-read-only value)
    value))

(defun ffap-read-only-other-window (filename)
  "Like `ffap', but put buffer in another window and mark as read-only.
Only intended for interactive use."
  (interactive (list (ffap-prompter nil " read only other window")))
  (let ((value (ffap-other-window filename)))
    (ffap--toggle-read-only value)
    value))

(defun ffap-read-only-other-frame (filename)
  "Like `ffap', but put buffer in another frame and mark as read-only.
Only intended for interactive use."
  (interactive (list (ffap-prompter nil " read only other frame")))
  (let ((value (ffap-other-frame filename)))
    (ffap--toggle-read-only value)
    value))

(defun ffap-read-only-other-tab (filename)
  "Like `ffap', but put buffer in another tab and mark as read-only.
Only intended for interactive use."
  (interactive (list (ffap-prompter nil " read only other tab")))
  (let ((value (window-buffer (ffap-other-tab filename))))
    (ffap--toggle-read-only value)
    value))

(defun ffap-alternate-file (filename)
  "Like `ffap' and `find-alternate-file'.
Only intended for interactive use."
  (interactive (list (ffap-prompter nil " alternate file")))
  (let ((ffap-file-finder 'find-alternate-file))
    (find-file-at-point filename)))

(defun ffap-alternate-file-other-window (filename)
  "Like `ffap' and `find-alternate-file-other-window'.
Only intended for interactive use."
  (interactive (list (ffap-prompter nil " alternate file other window")))
  (let ((ffap-file-finder 'find-alternate-file-other-window))
    (find-file-at-point filename)))

(defun ffap-literally (filename)
  "Like `ffap' and command `find-file-literally'.
Only intended for interactive use."
  (interactive (list (ffap-prompter nil " literally")))
  (let ((ffap-file-finder 'find-file-literally))
    (find-file-at-point filename)))

(defalias 'find-file-literally-at-point 'ffap-literally)

\f
;;; Hooks for Gnus, VM, Rmail:
;;
;; If you do not like these bindings, write versions with whatever
;; bindings you would prefer.

(defun ffap-ro-mode-hook ()
  "Bind `ffap-next' and `ffap-menu' to \\`M-l' and \\`M-m', resp."
  (local-set-key "\M-l" 'ffap-next)
  (local-set-key "\M-m" 'ffap-menu))

(defun ffap-gnus-hook ()
  "Bind `ffap-gnus-next' and `ffap-gnus-menu' to \\`M-l' and \\`M-m', resp."
  ;; message-id's
  (setq-local thing-at-point-default-mail-uri-scheme "news")
  ;; Note "l", "L", "m", "M" are taken:
  (local-set-key "\M-l" 'ffap-gnus-next)
  (local-set-key "\M-m" 'ffap-gnus-menu))

(defvar gnus-summary-buffer)
(defvar gnus-article-buffer)

;; This code is called from gnus.
(declare-function gnus-summary-select-article "gnus-sum"
                  (&optional all-headers force pseudo article))

(declare-function gnus-configure-windows "gnus-win"
                  (setting &optional force))

(defun ffap-gnus-wrapper (form)		; used by both commands below
  (and (eq (current-buffer) (get-buffer gnus-summary-buffer))
       (gnus-summary-select-article))	; get article of current line
  ;; Preserve selected buffer, but do not do save-window-excursion,
  ;; since we want to see any window created by the form.  Temporarily
  ;; select the article buffer, so we can see any point movement.
  (let ((sb (window-buffer)))
    (gnus-configure-windows 'article)
    (pop-to-buffer gnus-article-buffer)
    (widen)
    ;; Skip headers for ffap-gnus-next (which will wrap around)
    (if (eq (point) (point-min)) (search-forward "\n\n" nil t))
    (unwind-protect
	(eval form)
      (pop-to-buffer sb))))

(defun ffap-gnus-next ()
  "Run `ffap-next' in the gnus article buffer."
  (interactive) (ffap-gnus-wrapper '(ffap-next nil t)))

(defun ffap-gnus-menu ()
  "Run `ffap-menu' in the gnus article buffer."
  (interactive) (ffap-gnus-wrapper '(ffap-menu)))

\f

;;;###autoload
(defun dired-at-point (&optional filename)
  "Start Dired, defaulting to file at point.  See `ffap'.
If `dired-at-point-require-prefix' is set, the prefix meaning is reversed."
  (interactive)
  (if (and (called-interactively-p 'interactive)
	   (if dired-at-point-require-prefix
	       (not current-prefix-arg)
	     current-prefix-arg))
      (let (current-prefix-arg)		; already interpreted
	(call-interactively ffap-directory-finder))
    (or filename (setq filename (dired-at-point-prompter)))
    (let ((url (ffap-url-p filename)))
      (cond
       (url
	(funcall ffap-url-fetcher url))
       ((and ffap-dired-wildcards
	     (string-match ffap-dired-wildcards filename))
	(funcall ffap-directory-finder filename))
       ((file-exists-p filename)
	(if (file-directory-p filename)
	    (funcall ffap-directory-finder
		     (expand-file-name filename))
	  (funcall ffap-directory-finder
		   (concat (expand-file-name filename) "*"))))
       ((and (file-writable-p
	      (or (file-name-directory (directory-file-name filename))
		  filename))
	     (y-or-n-p "Directory does not exist, create it? "))
	(make-directory filename)
	(funcall ffap-directory-finder filename))
       (t
	(signal 'file-missing (list "Opening directory"
				    "No such file or directory"
				    filename)))))))

(defun dired-at-point-prompter (&optional guess)
  ;; Does guess and prompt step for find-file-at-point.
  ;; Extra complication for the temporary highlighting.
  (unwind-protect
      (ffap-read-file-or-url
       (cond
	((eq ffap-directory-finder 'list-directory)
	 "List directory (brief): ")
	(ffap-url-regexp "Dired file or URL: ")
	(t "Dired file: "))
       (prog1
	   (setq guess
		 (let ((guess (or guess (ffap-guesser))))
		   (cond
		    ((null guess) nil)
		    ((ffap-url-p guess))
		    ((ffap-file-remote-p guess)
		     guess)
		    ((progn
		       (setq guess (abbreviate-file-name
				    (expand-file-name guess)))
		       ;; Interpret local directory as a directory.
		       (file-directory-p guess))
		     (file-name-as-directory guess))
		    ;; Get directory component from local files.
		    ((file-regular-p guess)
		     (file-name-directory guess))
		    (guess))))
	 (and guess (ffap-highlight))))
    (ffap-highlight t)))
\f
;;; ffap-dired-other-*, ffap-list-directory commands:

(defun ffap-dired-other-window ()
  "Like `dired-at-point', but put buffer in another window.
Only intended for interactive use."
  (interactive)
  (let (value)
    (switch-to-buffer-other-window
     (save-window-excursion
       (setq value (call-interactively 'dired-at-point))
       (current-buffer)))
    value))

(defun ffap-dired-other-frame ()
  "Like `dired-at-point', but put buffer in another frame.
Only intended for interactive use."
  (interactive)
  ;; Extra code works around dedicated windows:
  (let* ((win (selected-window))
	 (wdp (window-dedicated-p win))
	 value)
    (unwind-protect
	(progn
	  (set-window-dedicated-p win nil)
	  (switch-to-buffer-other-frame
	   (save-window-excursion
	     (setq value (call-interactively 'dired-at-point))
	     (current-buffer))))
      (set-window-dedicated-p win wdp))
    value))

(defun ffap-list-directory ()
  "Like `dired-at-point' and `list-directory'.
Only intended for interactive use."
  (interactive)
  (let ((ffap-directory-finder 'list-directory))
    (call-interactively 'dired-at-point)))

\f
;;; Hooks to put in `file-name-at-point-functions':

;;;###autoload
(defun ffap-guess-file-name-at-point ()
  "Try to get a file name at point.
This hook is intended to be put in `file-name-at-point-functions'."
  ;; ffap-guesser can signal an error, and we don't want that when,
  ;; e.g., the user types M-n at the "C-x C-f" prompt.
  (let ((guess (ignore-errors (ffap-guesser))))
    (when (stringp guess)
      (let ((url (ffap-url-p guess)))
	(or url
	    (progn
	      (unless (ffap-file-remote-p guess)
		(setq guess
		      (abbreviate-file-name (expand-file-name guess))))
	      (if (file-directory-p guess)
		  (file-name-as-directory guess)
		guess)))))))
\f
;;; Offer default global bindings (`ffap-bindings'):

(defvar ffap-bindings
   '((global-set-key [S-mouse-3] 'ffap-at-mouse)
     (global-set-key [C-S-mouse-3] 'ffap-menu)

     (global-set-key [remap find-file] 'find-file-at-point)
     (global-set-key [remap find-file-read-only] 'ffap-read-only)
     (global-set-key [remap find-alternate-file] 'ffap-alternate-file)

     (global-set-key [remap find-file-other-window] 'ffap-other-window)
     (global-set-key [remap find-file-other-frame] 'ffap-other-frame)
     (global-set-key [remap find-file-other-tab] 'ffap-other-tab)
     (global-set-key [remap find-file-read-only-other-window] 'ffap-read-only-other-window)
     (global-set-key [remap find-file-read-only-other-frame] 'ffap-read-only-other-frame)

     (global-set-key [remap dired] 'dired-at-point)
     (global-set-key [remap dired-other-window] 'ffap-dired-other-window)
     (global-set-key [remap dired-other-frame] 'ffap-dired-other-frame)
     (global-set-key [remap list-directory] 'ffap-list-directory)

     (add-hook 'gnus-summary-mode-hook 'ffap-gnus-hook)
     (add-hook 'gnus-article-mode-hook 'ffap-gnus-hook)
     (add-hook 'vm-mode-hook 'ffap-ro-mode-hook)
     (add-hook 'rmail-mode-hook 'ffap-ro-mode-hook))
     "List of binding forms evaluated by function `ffap-bindings'.
A reasonable ffap installation needs just this one line:
  (ffap-bindings)
Of course if you do not like these bindings, just roll your own!")

;;;###autoload
(defun ffap-bindings ()
  "Evaluate the forms in variable `ffap-bindings'."
  (interactive)
  (eval (cons 'progn ffap-bindings)))

(define-obsolete-variable-alias 'ffap-newsgroup-regexp 'thing-at-point-newsgroup-regexp "30.1")
(define-obsolete-variable-alias 'ffap-newsgroup-heads  'thing-at-point-newsgroup-heads "30.1")
(define-obsolete-function-alias 'ffap-newsgroup-p #'thing-at-point-newsgroup-p "30.1")

\f
(provide 'ffap)

;;; ffap.el ends here