path: root/lisp/complete.el

;;; complete.el --- partial completion mechanism plus other goodies

;; Copyright (C) 1990, 1991, 1992, 1993, 1999, 2000, 2001, 2002, 2003,
;;   2004, 2005, 2006, 2007 Free Software Foundation, Inc.

;; Author: Dave Gillespie <daveg@synaptics.com>
;; Keywords: abbrev convenience
;; Special thanks to Hallvard Furuseth for his many ideas and contributions.

;; 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, 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; see the file COPYING.  If not, write to the
;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
;; Boston, MA 02110-1301, USA.

;;; Commentary:

;; Extended completion for the Emacs minibuffer.
;;
;; The basic idea is that the command name or other completable text is
;; divided into words and each word is completed separately, so that
;; "M-x p-b" expands to "M-x print-buffer".  If the entry is ambiguous
;; each word is completed as much as possible and then the cursor is
;; left at the first position where typing another letter will resolve
;; the ambiguity.
;;
;; Word separators for this purpose are hyphen, space, and period.
;; These would most likely occur in command names, Info menu items,
;; and file names, respectively.  But all word separators are treated
;; alike at all times.
;;
;; This completion package replaces the old-style completer's key
;; bindings for TAB, SPC, RET, and `?'.  The old completer is still
;; available on the Meta versions of those keys.  If you set
;; PC-meta-flag to nil, the old completion keys will be left alone
;; and the partial completer will use the Meta versions of the keys.


;; Usage:  M-x partial-completion-mode.  During completable minibuffer entry,
;;
;;     TAB    means to do a partial completion;
;;     SPC    means to do a partial complete-word;
;;     RET    means to do a partial complete-and-exit;
;;     ?      means to do a partial completion-help.
;;
;; If you set PC-meta-flag to nil, then TAB, SPC, RET, and ? perform
;; original Emacs completions, and M-TAB etc. do partial completion.
;; To do this, put the command,
;;
;;       (setq PC-meta-flag nil)
;;
;; in your .emacs file.  To load partial completion automatically, put
;;
;;       (partial-completion-mode t)
;;
;; in your .emacs file, too.  Things will be faster if you byte-compile
;; this file when you install it.
;;
;; As an extra feature, in cases where RET would not normally
;; complete (such as `C-x b'), the M-RET key will always do a partial
;; complete-and-exit.  Thus `C-x b f.c RET' will select or create a
;; buffer called "f.c", but `C-x b f.c M-RET' will select the existing
;; buffer whose name matches that pattern (perhaps "filing.c").
;; (PC-meta-flag does not affect this behavior; M-RET used to be
;; undefined in this situation.)
;;
;; The regular M-TAB (lisp-complete-symbol) command also supports
;; partial completion in this package.

;; In addition, this package includes a feature for accessing include
;; files.  For example, `C-x C-f <sys/time.h> RET' reads the file
;; /usr/include/sys/time.h.  The variable PC-include-file-path is a
;; list of directories in which to search for include files.  Completion
;; is supported in include file names.


;;; Code:

(defgroup partial-completion nil
  "Partial Completion of items."
  :prefix "pc-"
  :group 'minibuffer
  :group 'convenience)

(defcustom PC-first-char 'find-file
  "Control how the first character of a string is to be interpreted.
If nil, the first character of a string is not taken literally if it is a word
delimiter, so that \".e\" matches \"*.e*\".
If t, the first character of a string is always taken literally even if it is a
word delimiter, so that \".e\" matches \".e*\".
If non-nil and non-t, the first character is taken literally only for file name
completion."
  :type '(choice (const :tag "delimiter" nil)
		 (const :tag "literal" t)
		 (other :tag "find-file" find-file))
  :group 'partial-completion)

(defcustom PC-meta-flag t
  "If non-nil, TAB means PC completion and M-TAB means normal completion.
Otherwise, TAB means normal completion and M-TAB means Partial Completion."
  :type 'boolean
  :group 'partial-completion)

(defcustom PC-word-delimiters "-_. "
  "A string of characters treated as word delimiters for completion.
Some arcane rules:
If `]' is in this string, it must come first.
If `^' is in this string, it must not come first.
If `-' is in this string, it must come first or right after `]'.
In other words, if S is this string, then `[S]' must be a valid Emacs regular
expression (not containing character ranges like `a-z')."
  :type 'string
  :group 'partial-completion)

(defcustom PC-include-file-path '("/usr/include" "/usr/local/include")
  "A list of directories in which to look for include files.
If nil, means use the colon-separated path in the variable $INCPATH instead."
  :type '(repeat directory)
  :group 'partial-completion)

(defcustom PC-disable-includes nil
  "If non-nil, include-file support in \\[find-file] is disabled."
  :type 'boolean
  :group 'partial-completion)

(defvar PC-default-bindings t
  "If non-nil, default partial completion key bindings are suppressed.")

(defvar PC-env-vars-alist nil
  "A list of the environment variable names and values.")


(defun PC-bindings (bind)
  (let ((completion-map minibuffer-local-completion-map)
	(must-match-map minibuffer-local-must-match-map))
    (cond ((not bind)
	   ;; These bindings are the default bindings.  It would be better to
	   ;; restore the previous bindings.
	   (define-key read-expression-map "\e\t" 'lisp-complete-symbol)

	   (define-key completion-map "\t"	'minibuffer-complete)
	   (define-key completion-map " "	'minibuffer-complete-word)
	   (define-key completion-map "?"	'minibuffer-completion-help)

	   (define-key must-match-map "\r"	'minibuffer-complete-and-exit)
	   (define-key must-match-map "\n"	'minibuffer-complete-and-exit)

	   (define-key global-map [remap lisp-complete-symbol]	nil))
	  (PC-default-bindings
	   (define-key read-expression-map "\e\t" 'PC-lisp-complete-symbol)

	   (define-key completion-map "\t"	'PC-complete)
	   (define-key completion-map " "	'PC-complete-word)
	   (define-key completion-map "?"	'PC-completion-help)

	   (define-key completion-map "\e\t"	'PC-complete)
	   (define-key completion-map "\e "	'PC-complete-word)
	   (define-key completion-map "\e\r"	'PC-force-complete-and-exit)
	   (define-key completion-map "\e\n"	'PC-force-complete-and-exit)
	   (define-key completion-map "\e?"	'PC-completion-help)

	   (define-key must-match-map "\r"	'PC-complete-and-exit)
	   (define-key must-match-map "\n"	'PC-complete-and-exit)

	   (define-key must-match-map "\e\r"	'PC-complete-and-exit)
	   (define-key must-match-map "\e\n"	'PC-complete-and-exit)

	   (define-key global-map [remap lisp-complete-symbol]	'PC-lisp-complete-symbol)))))

(defvar PC-do-completion-end nil
  "Internal variable used by `PC-do-completion'.")

(make-variable-buffer-local 'PC-do-completion-end)

(defvar PC-goto-end nil
   "Internal variable set in `PC-do-completion', used in
`choose-completion-string-functions'.")

(make-variable-buffer-local 'PC-goto-end)

;;;###autoload
(define-minor-mode partial-completion-mode
  "Toggle Partial Completion mode.
With prefix ARG, turn Partial Completion mode on if ARG is positive.

When Partial Completion mode is enabled, TAB (or M-TAB if `PC-meta-flag' is
nil) is enhanced so that if some string is divided into words and each word is
delimited by a character in `PC-word-delimiters', partial words are completed
as much as possible and `*' characters are treated likewise in file names.

For example, M-x p-c-m expands to M-x partial-completion-mode since no other
command begins with that sequence of characters, and
\\[find-file] f_b.c TAB might complete to foo_bar.c if that file existed and no
other file in that directory begins with that sequence of characters.

Unless `PC-disable-includes' is non-nil, the `<...>' sequence is interpreted
specially in \\[find-file].  For example,
\\[find-file] <sys/time.h> RET finds the file `/usr/include/sys/time.h'.
See also the variable `PC-include-file-path'.

Partial Completion mode extends the meaning of `completion-auto-help' (which
see), so that if it is neither nil nor t, Emacs shows the `*Completions*'
buffer only on the second attempt to complete.  That is, if TAB finds nothing
to complete, the first TAB just says \"Next char not unique\" and the
second TAB brings up the `*Completions*' buffer."
  :global t :group 'partial-completion
  ;; Deal with key bindings...
  (PC-bindings partial-completion-mode)
  ;; Deal with include file feature...
  (cond ((not partial-completion-mode)
	 (remove-hook 'find-file-not-found-functions 'PC-look-for-include-file))
	((not PC-disable-includes)
	 (add-hook 'find-file-not-found-functions 'PC-look-for-include-file)))
  ;; Adjust the completion selection in *Completion* buffers to the way
  ;; we work.  The default minibuffer completion code only completes the
  ;; text before point and leaves the text after point alone (new in
  ;; Emacs-22).  In contrast we use the whole text and we even sometimes
  ;; move point to a place before EOB, to indicate the first position where
  ;; there's a difference, so when the user uses choose-completion, we have
  ;; to trick choose-completion into replacing the whole minibuffer text
  ;; rather than only the text before point.  --Stef
  (funcall
   (if partial-completion-mode 'add-hook 'remove-hook)
   'choose-completion-string-functions
   (lambda (choice buffer mini-p base-size)
     ;; When completing M-: (lisp- ) with point before the ), it is
     ;; not appropriate to go to point-max (unlike the filename case).
     (if (and (not PC-goto-end)
              mini-p)
         (goto-char (point-max))
       ;; Need a similar hack for the non-minibuffer-case -- gm.
       (when PC-do-completion-end
         (goto-char PC-do-completion-end)
         (setq PC-do-completion-end nil)))
     (setq PC-goto-end nil)
     nil))
  ;; Build the env-completion and mapping table.
  (when (and partial-completion-mode (null PC-env-vars-alist))
    (setq PC-env-vars-alist
          (mapcar (lambda (string)
                    (let ((d (string-match "=" string)))
                      (cons (concat "$" (substring string 0 d))
                            (and d (substring string (1+ d))))))
                  process-environment))))


(defun PC-complete ()
  "Like minibuffer-complete, but allows \"b--di\"-style abbreviations.
For example, \"M-x b--di\" would match `byte-recompile-directory', or any
name which consists of three or more words, the first beginning with \"b\"
and the third beginning with \"di\".

The pattern \"b--d\" is ambiguous for `byte-recompile-directory' and
`beginning-of-defun', so this would produce a list of completions
just like when normal Emacs completions are ambiguous.

Word-delimiters for the purposes of Partial Completion are \"-\", \"_\",
\".\", and SPC."
  (interactive)
  (if (PC-was-meta-key)
      (minibuffer-complete)
    ;; If the previous command was not this one,
    ;; never scroll, always retry completion.
    (or (eq last-command this-command)
	(setq minibuffer-scroll-window nil))
    (let ((window minibuffer-scroll-window))
      ;; If there's a fresh completion window with a live buffer,
      ;; and this command is repeated, scroll that window.
      (if (and window (window-buffer window)
	       (buffer-name (window-buffer window)))
	  (with-current-buffer (window-buffer window)
	    (if (pos-visible-in-window-p (point-max) window)
		(set-window-start window (point-min) nil)
	      (scroll-other-window)))
	(PC-do-completion nil)))))


(defun PC-complete-word ()
  "Like `minibuffer-complete-word', but allows \"b--di\"-style abbreviations.
See `PC-complete' for details.
This can be bound to other keys, like `-' and `.', if you wish."
  (interactive)
  (if (eq (PC-was-meta-key) PC-meta-flag)
      (if (eq last-command-char ? )
	  (minibuffer-complete-word)
	(self-insert-command 1))
    (self-insert-command 1)
    (if (eobp)
	(PC-do-completion 'word))))


(defun PC-complete-space ()
  "Like `minibuffer-complete-word', but allows \"b--di\"-style abbreviations.
See `PC-complete' for details.
This is suitable for binding to other keys which should act just like SPC."
  (interactive)
  (if (eq (PC-was-meta-key) PC-meta-flag)
      (minibuffer-complete-word)
    (insert " ")
    (if (eobp)
	(PC-do-completion 'word))))


(defun PC-complete-and-exit ()
  "Like `minibuffer-complete-and-exit', but allows \"b--di\"-style abbreviations.
See `PC-complete' for details."
  (interactive)
  (if (eq (PC-was-meta-key) PC-meta-flag)
      (minibuffer-complete-and-exit)
    (PC-do-complete-and-exit)))

(defun PC-force-complete-and-exit ()
  "Like `minibuffer-complete-and-exit', but allows \"b--di\"-style abbreviations.
See `PC-complete' for details."
  (interactive)
  (let ((minibuffer-completion-confirm nil))
    (PC-do-complete-and-exit)))

(defun PC-do-complete-and-exit ()
  (cond
   ((= (point-max) (minibuffer-prompt-end))
    ;; Duplicate the "bug" that Info-menu relies on...
    (exit-minibuffer))
   ((eq minibuffer-completion-confirm 'confirm-only)
    (if (or (eq last-command this-command)
            (test-completion (field-string)
                             minibuffer-completion-table
                             minibuffer-completion-predicate))
        (exit-minibuffer)
      (PC-temp-minibuffer-message " [Confirm]")))
   (t
    (let ((flag (PC-do-completion 'exit)))
      (and flag
	   (if (or (eq flag 'complete)
		   (not minibuffer-completion-confirm))
	       (exit-minibuffer)
	     (PC-temp-minibuffer-message " [Confirm]")))))))


(defun PC-completion-help ()
  "Like `minibuffer-completion-help', but allows \"b--di\"-style abbreviations.
See `PC-complete' for details."
  (interactive)
  (if (eq (PC-was-meta-key) PC-meta-flag)
      (minibuffer-completion-help)
    (PC-do-completion 'help)))

(defun PC-was-meta-key ()
  (or (/= (length (this-command-keys)) 1)
      (let ((key (aref (this-command-keys) 0)))
	(if (integerp key)
	    (>= key 128)
	  (not (null (memq 'meta (event-modifiers key))))))))


(defvar PC-ignored-extensions 'empty-cache)
(defvar PC-delims 'empty-cache)
(defvar PC-ignored-regexp nil)
(defvar PC-word-failed-flag nil)
(defvar PC-delim-regex nil)
(defvar PC-ndelims-regex nil)
(defvar PC-delims-list nil)

(defvar PC-completion-as-file-name-predicate
  (lambda () minibuffer-completing-file-name)
  "A function testing whether a minibuffer completion now will work filename-style.
The function takes no arguments, and typically looks at the value
of `minibuffer-completion-table' and the minibuffer contents.")

;; Returns the sequence of non-delimiter characters that follow regexp in string.
(defun PC-chunk-after (string regexp)
  (if (not (string-match regexp string))
      (let ((message "String %s didn't match regexp %s"))
	(message message string regexp)
	(error message string regexp)))
  (let ((result (substring string (match-end 0))))
    ;; result may contain multiple chunks
    (if (string-match PC-delim-regex result)
	(setq result (substring result 0 (match-beginning 0))))
    result))

(defun test-completion-ignore-case (str table pred)
  "Like `test-completion', but ignores case when possible."
  ;; Binding completion-ignore-case to nil ensures, for compatibility with
  ;; standard completion, that the return value is exactly one of the
  ;; possibilities.  Do this binding only if pred is nil, out of paranoia;
  ;; perhaps it is safe even if pred is non-nil.
  (if pred
      (test-completion str table pred)
    (let ((completion-ignore-case nil))
      (test-completion str table pred))))

;; The following function is an attempt to work around two problems:

;; (1) When complete.el was written, (try-completion "" '(("") (""))) used to
;; return the value "".  With a change from 2002-07-07 it returns t which caused
;; `PC-lisp-complete-symbol' to fail with a "Wrong type argument: sequencep, t"
;; error.  `PC-try-completion' returns STRING in this case.

;; (2) (try-completion "" '((""))) returned t before the above-mentioned change.
;; Since `PC-chop-word' operates on the return value of `try-completion' this
;; case might have provoked a similar error as in (1).  `PC-try-completion'
;; returns "" instead.  I don't know whether this is a real problem though.

;; Since `PC-try-completion' is not a guaranteed to fix these bugs reliably, you
;; should try to look at the following discussions when you encounter problems:
;; - emacs-pretest-bug ("Partial Completion" starting 2007-02-23),
;; - emacs-devel ("[address-of-OP: Partial completion]" starting 2007-02-24),
;; - emacs-devel ("[address-of-OP: EVAL and mouse selection in *Completions*]"
;;   starting 2007-03-05).
(defun PC-try-completion (string alist &optional predicate)
  "Like `try-completion' but return STRING instead of t."
  (let ((result (try-completion string alist predicate)))
    (if (eq result t) string result)))

;; TODO document MODE magic...
(defun PC-do-completion (&optional mode beg end goto-end)
  "Internal function to do the work of partial completion.
Text to be completed lies between BEG and END.  Normally when
replacing text in the minibuffer, this function replaces up to
point-max (as is appropriate for completing a file name).  If
GOTO-END is non-nil, however, it instead replaces up to END."
  (or beg (setq beg (minibuffer-prompt-end)))
  (or end (setq end (point-max)))
  (let* ((table (if (eq minibuffer-completion-table 'read-file-name-internal)
                    'PC-read-file-name-internal
                    minibuffer-completion-table))
	 (pred minibuffer-completion-predicate)
	 (filename (funcall PC-completion-as-file-name-predicate))
	 (dirname nil) ; non-nil only if a filename is being completed
	 ;; The following used to be "(dirlength 0)" which caused the erasure of
	 ;; the entire buffer text before `point' when inserting a completion
	 ;; into a buffer.
	 dirlength
	 (str (buffer-substring beg end))
	 (incname (and filename (string-match "<\\([^\"<>]*\\)>?$" str)))
	 (ambig nil)
	 basestr origstr
	 env-on
	 regex
	 p offset
         abbreviated
	 (poss nil)
	 helpposs
	 (case-fold-search completion-ignore-case))

    ;; Check if buffer contents can already be considered complete
    (if (and (eq mode 'exit)
	     (test-completion str table pred))
	(progn
	  ;; If completion-ignore-case is non-nil, insert the
	  ;; completion string since that may have a different case.
	  (when completion-ignore-case
	    (setq str (PC-try-completion str table pred))
	    (delete-region beg end)
	    (insert str))
	  'complete)

      ;; Do substitutions in directory names
      (and filename
           (setq basestr (or (file-name-directory str) ""))
           (setq dirlength (length basestr))
	   ;; Do substitutions in directory names
           (setq p (substitute-in-file-name basestr))
           (not (string-equal basestr p))
           (setq str (concat p (file-name-nondirectory str)))
           (progn
	     (delete-region beg end)
	     (insert str)
	     (setq end (+ beg (length str)))))

      ;; Prepare various delimiter strings
      (or (equal PC-word-delimiters PC-delims)
	  (setq PC-delims PC-word-delimiters
		PC-delim-regex (concat "[" PC-delims "]")
		PC-ndelims-regex (concat "[^" PC-delims "]*")
		PC-delims-list (append PC-delims nil)))

      ;; Add wildcards if necessary
      (and filename
           (let ((dir (file-name-directory str))
                 (file (file-name-nondirectory str))
		 ;; The base dir for file-completion is passed in `predicate'.
		 (default-directory (expand-file-name pred)))
             (while (and (stringp dir) (not (file-directory-p dir)))
               (setq dir (directory-file-name dir))
               (setq file (concat (replace-regexp-in-string
                                   PC-delim-regex "*\\&"
                                   (file-name-nondirectory dir))
                                  "*/" file))
               (setq dir (file-name-directory dir)))
             (setq origstr str str (concat dir file))))

      ;; Look for wildcard expansions in directory name
      (and filename
	   (string-match "\\*.*/" str)
	   (let ((pat str)
		 ;; The base dir for file-completion is passed in `predicate'.
		 (default-directory (expand-file-name pred))
		 files)
	     (setq p (1+ (string-match "/[^/]*\\'" pat)))
	     (while (setq p (string-match PC-delim-regex pat p))
	       (setq pat (concat (substring pat 0 p)
				 "*"
				 (substring pat p))
		     p (+ p 2)))
	     (setq files (file-expand-wildcards (concat pat "*")))
	     (if files
		 (let ((dir (file-name-directory (car files)))
		       (p files))
		   (while (and (setq p (cdr p))
			       (equal dir (file-name-directory (car p)))))
		   (if p
		       (setq filename nil table nil pred nil
			     ambig t)
		     (delete-region beg end)
		     (setq str (concat dir (file-name-nondirectory str)))
		     (insert str)
		     (setq end (+ beg (length str)))))
	       (if origstr
                       ;; If the wildcards were introduced by us, it's
                       ;; possible that PC-read-file-name-internal can
                       ;; still find matches for the original string
                       ;; even if we couldn't, so remove the added
                       ;; wildcards.
                   (setq str origstr)
		 (setq filename nil table nil pred nil)))))

      ;; Strip directory name if appropriate
      (if filename
	  (if incname
	      (setq basestr (substring str incname)
		    dirname (substring str 0 incname))
	    (setq basestr (file-name-nondirectory str)
		  dirname (file-name-directory str))
	    ;; Make sure str is consistent with its directory and basename
	    ;; parts.  This is important on DOZe'NT systems when str only
	    ;; includes a drive letter, like in "d:".
	    (setq str (concat dirname basestr)))
	(setq basestr str))

      ;; Convert search pattern to a standard regular expression
      (setq regex (regexp-quote basestr)
	    offset (if (and (> (length regex) 0)
			    (not (eq (aref basestr 0) ?\*))
			    (or (eq PC-first-char t)
				(and PC-first-char filename))) 1 0)
	    p offset)
      (while (setq p (string-match PC-delim-regex regex p))
	(if (eq (aref regex p) ? )
	    (setq regex (concat (substring regex 0 p)
				PC-ndelims-regex
				PC-delim-regex
				(substring regex (1+ p)))
		  p (+ p (length PC-ndelims-regex) (length PC-delim-regex)))
	  (let ((bump (if (memq (aref regex p)
				'(?$ ?^ ?\. ?* ?+ ?? ?[ ?] ?\\))
			  -1 0)))
	    (setq regex (concat (substring regex 0 (+ p bump))
				PC-ndelims-regex
				(substring regex (+ p bump)))
		  p (+ p (length PC-ndelims-regex) 1)))))
      (setq p 0)
      (if filename
	  (while (setq p (string-match "\\\\\\*" regex p))
	    (setq regex (concat (substring regex 0 p)
				"[^/]*"
				(substring regex (+ p 2))))))
      ;;(setq the-regex regex)
      (setq regex (concat "\\`" regex))

      (and (> (length basestr) 0)
           (= (aref basestr 0) ?$)
           (setq env-on t
                 table PC-env-vars-alist
                 pred nil))

      ;; Find an initial list of possible completions
        (unless (setq p (string-match (concat PC-delim-regex
					     (if filename "\\|\\*" ""))
				     str
                                      (+ (length dirname) offset)))

	  ;; Minibuffer contains no hyphens -- simple case!
          (setq poss (all-completions (if env-on basestr str)
				      table
				      pred))
          (unless (or poss (string-equal str ""))
            ;; Try completion as an abbreviation, e.g. "mvb" ->
            ;; "m-v-b" -> "multiple-value-bind", but only for
            ;; non-empty strings.
            (setq origstr str
                  abbreviated t)
            (if filename
                (cond
                  ;; "alpha" or "/alpha" -> expand whole path.
                  ((string-match "^/?\\([A-Za-z0-9]+\\)$" str)
                   (setq
                    basestr ""
                    p nil
		    poss (file-expand-wildcards
                          (concat "/"
                                  (mapconcat #'list (match-string 1 str) "*/")
                                  "*"))
                    beg (1- beg)))
                  ;; Alphanumeric trailer -> expand trailing file
                  ((string-match "^\\(.+/\\)\\([A-Za-z0-9]+\\)$" str)
                   (setq regex (concat "\\`"
                                        (mapconcat #'list
                                                   (match-string 2 str)
                                                   "[A-Za-z0-9]*[^A-Za-z0-9]"))
                          p (1+ (length (match-string 1 str))))))
                (setq regex (concat "\\`" (mapconcat #'list str "[^-]*-"))
                      p 1))))
        (when p
	;; Use all-completions to do an initial cull.  This is a big win,
	;; since all-completions is written in C!
	(let ((compl (all-completions (if env-on
					  (file-name-nondirectory (substring str 0 p))
					(substring str 0 p))
                                      table
                                      pred)))
	  (setq p compl)
            (when (and compl abbreviated)
              (if filename
                  (progn
                    (setq p nil)
                    (dolist (x compl)
                      (when (string-match regex x)
                        (push x p)))
                    (setq basestr (try-completion "" p)))
                  (setq basestr (mapconcat 'list str "-"))
                  (delete-region beg end)
                  (setq end (+ beg (length basestr)))
                  (insert basestr))))
	  (while p
	    (and (string-match regex (car p))
		 (progn
		   (set-text-properties 0 (length (car p)) '() (car p))
		   (setq poss (cons (car p) poss))))
            (setq p (cdr p))))

      ;; If table had duplicates, they can be here.
      (delete-dups poss)

      ;; Handle completion-ignored-extensions
      (and filename
           (not (eq mode 'help))
           (let ((p2 poss))

             ;; Build a regular expression representing the extensions list
             (or (equal completion-ignored-extensions PC-ignored-extensions)
                 (setq PC-ignored-regexp
                       (concat "\\("
                               (mapconcat
                                'regexp-quote
                                (setq PC-ignored-extensions
                                      completion-ignored-extensions)
                                "\\|")
                               "\\)\\'")))

             ;; Check if there are any without an ignored extension.
             ;; Also ignore `.' and `..'.
             (setq p nil)
             (while p2
               (or (string-match PC-ignored-regexp (car p2))
                   (string-match "\\(\\`\\|/\\)[.][.]?/?\\'" (car p2))
                   (setq p (cons (car p2) p)))
               (setq p2 (cdr p2)))

             ;; If there are "good" names, use them
             (and p (setq poss p))))

      ;; Now we have a list of possible completions

      (cond

       ;; No valid completions found
       ((null poss)
	(if (and (eq mode 'word)
		 (not PC-word-failed-flag))
	    (let ((PC-word-failed-flag t))
	      (delete-backward-char 1)
	      (PC-do-completion 'word))
               (when abbreviated
                 (delete-region beg end)
                 (insert origstr))
	  (beep)
	  (PC-temp-minibuffer-message (if ambig
					  " [Ambiguous dir name]"
					(if (eq mode 'help)
					    " [No completions]"
					  " [No match]")))
	  nil))

       ;; More than one valid completion found
       ((or (cdr (setq helpposs poss))
	    (memq mode '(help word)))

	;; Is the actual string one of the possible completions?
	(setq p (and (not (eq mode 'help)) poss))
	(while (and p
		    (not (string-equal (car p) basestr)))
	  (setq p (cdr p)))
	(and p (null mode)
	     (PC-temp-minibuffer-message " [Complete, but not unique]"))
	(if (and p
		 (not (and (null mode)
			   (eq this-command last-command))))
	    t

	  ;; If ambiguous, try for a partial completion
	  (let ((improved nil)
		prefix
		(pt nil)
		(skip "\\`"))

	    ;; Check if next few letters are the same in all cases
	    (if (and (not (eq mode 'help))
		     (setq prefix (PC-try-completion
				   (PC-chunk-after basestr skip) poss)))
		(let ((first t) i)
		  ;; Retain capitalization of user input even if
		  ;; completion-ignore-case is set.
		  (if (eq mode 'word)
		      (setq prefix (PC-chop-word prefix basestr)))
		  (goto-char (+ beg (length dirname)))
		  (while (and (progn
				(setq i 0) ; index into prefix string
				(while (< i (length prefix))
				  (if (and (< (point) end)
					   (eq (downcase (aref prefix i))
					       (downcase (following-char))))
				      ;; same char (modulo case); no action
				      (forward-char 1)
				    (if (and (< (point) end)
					     (and (looking-at " ")
                                                  (memq (aref prefix i)
							PC-delims-list)))
					;; replace " " by the actual delimiter
					(progn
					  (delete-char 1)
					  (insert (substring prefix i (1+ i))))
				      ;; insert a new character
				      (progn
                                        (and filename (looking-at "\\*")
                                             (progn
                                               (delete-char 1)
                                               (setq end (1- end))))
					(setq improved t)
                                        (insert (substring prefix i (1+ i)))
					(setq end (1+ end)))))
				  (setq i (1+ i)))
				(or pt (setq pt (point)))
				(looking-at PC-delim-regex))
			      (setq skip (concat skip
						 (regexp-quote prefix)
						 PC-ndelims-regex)
				    prefix (PC-try-completion
					    (PC-chunk-after
					     ;; not basestr, because that does
					     ;; not reflect insertions
					     (buffer-substring
					      (+ beg (length dirname)) end)
					     skip)
					    (mapcar
                                             (lambda (x)
                                               (when (string-match skip x)
                                                 (substring x (match-end 0))))
					     poss)))
			      (or (> i 0) (> (length prefix) 0))
			      (or (not (eq mode 'word))
				  (and first (> (length prefix) 0)
				       (setq first nil
					     prefix (substring prefix 0 1))))))
		  (goto-char (if (eq mode 'word) end
			       (or pt beg)))))

	    (if (and (eq mode 'word)
		     (not PC-word-failed-flag))

		(if improved

		    ;; We changed it... would it be complete without the space?
		    (if (test-completion (buffer-substring 1 (1- end))
                                         table pred)
			(delete-region (1- end) end)))

	      (if improved

		  ;; We changed it... enough to be complete?
		  (and (eq mode 'exit)
		       (test-completion-ignore-case (field-string) table pred))

		;; If totally ambiguous, display a list of completions
		(if (or (eq completion-auto-help t)
			(and completion-auto-help
			     (eq last-command this-command))
			(eq mode 'help))
                    (let ((prompt-end (minibuffer-prompt-end)))
                      (with-output-to-temp-buffer "*Completions*"
                        (display-completion-list (sort helpposs 'string-lessp))
                        (setq PC-do-completion-end end
                              PC-goto-end goto-end)
                        (with-current-buffer standard-output
                          ;; Record which part of the buffer we are completing
                          ;; so that choosing a completion from the list
                          ;; knows how much old text to replace.
                          ;; This was briefly nil in the non-dirname case.
                          ;; However, if one calls PC-lisp-complete-symbol
                          ;; on "(ne-f" with point on the hyphen, PC offers
                          ;; all completions starting with "(ne", some of
                          ;; which do not match the "-f" part (maybe it
                          ;; should not, but it does). In such cases,
                          ;; completion gets confused trying to figure out
                          ;; how much to replace, so we tell it explicitly
                          ;; (ie, the number of chars in the buffer before beg).
                          ;;
                          ;; Note that choose-completion-string-functions
                          ;; plays around with point.
                          (setq completion-base-size (if dirname
                                                         dirlength
                                                       (- beg prompt-end))))))
                             (PC-temp-minibuffer-message " [Next char not unique]"))
                         ;; Expansion of filenames is not reversible,
                         ;; so just keep the prefix.
           (when (and abbreviated filename)
             (delete-region (point) end))
                         nil)))))

       ;; Only one possible completion
       (t
	(if (and (equal basestr (car poss))
                 (not (and env-on filename))
                 (not abbreviated))
	    (if (null mode)
		(PC-temp-minibuffer-message " [Sole completion]"))
	  (delete-region beg end)
	  (insert (format "%s"
			  (if filename
			      (substitute-in-file-name (concat dirname (car poss)))
			    (car poss)))))
	t)))))

(defun PC-chop-word (new old)
  (let ((i -1)
	(j -1))
    (while (and (setq i (string-match PC-delim-regex old (1+ i)))
		(setq j (string-match PC-delim-regex new (1+ j)))))
    (if (and j
	     (or (not PC-word-failed-flag)
		 (setq j (string-match PC-delim-regex new (1+ j)))))
	(substring new 0 (1+ j))
      new)))

(defvar PC-not-minibuffer nil)

(defun PC-temp-minibuffer-message (message)
  "A Lisp version of `temp_minibuffer_message' from minibuf.c."
  (cond (PC-not-minibuffer
	 (message "%s" message)
	 (sit-for 2)
	 (message ""))
	((fboundp 'temp-minibuffer-message)
	 (temp-minibuffer-message message))
	(t
	 (let ((point-max (point-max)))
	   (save-excursion
	     (goto-char point-max)
	     (insert message))
	   (let ((inhibit-quit t))
	     (sit-for 2)
	     (delete-region point-max (point-max))
	     (when quit-flag
	       (setq quit-flag nil
		     unread-command-events '(7))))))))

;; Does not need to be buffer-local (?) because only used when one
;; PC-l-c-s immediately follows another.
(defvar PC-lisp-complete-end nil
  "Internal variable used by `PC-lisp-complete-symbol'.")

(defun PC-lisp-complete-symbol ()
  "Perform completion on Lisp symbol preceding point.
That symbol is compared against the symbols that exist
and any additional characters determined by what is there
are inserted.
If the symbol starts just after an open-parenthesis,
only symbols with function definitions are considered.
Otherwise, all symbols with function definitions, values
or properties are considered."
  (interactive)
  (let* ((end
          (save-excursion
            (with-syntax-table lisp-mode-syntax-table
              (skip-syntax-forward "_w")
              (point))))
	 (beg (save-excursion
                (with-syntax-table lisp-mode-syntax-table
                  (backward-sexp 1)
                  (while (= (char-syntax (following-char)) ?\')
                    (forward-char 1))
                  (point))))
	 (minibuffer-completion-table obarray)
	 (minibuffer-completion-predicate
	  (if (eq (char-after (1- beg)) ?\()
	      'fboundp
	    (function (lambda (sym)
			(or (boundp sym) (fboundp sym)
			    (symbol-plist sym))))))
	 (PC-not-minibuffer t))
    ;; http://lists.gnu.org/archive/html/emacs-devel/2007-03/msg01211.html
    ;;
    ;; This deals with cases like running PC-l-c-s on "M-: (n-f".
    ;; The first call to PC-l-c-s expands this to "(ne-f", and moves
    ;; point to the hyphen [1]. If one calls PC-l-c-s immediately after,
    ;; then without the last-command check, one is offered all
    ;; completions of "(ne", which is presumably not what one wants.
    ;;
    ;; This is arguably (at least, it seems to be the existing intended
    ;; behaviour) what one _does_ want if point has been explicitly
    ;; positioned on the hyphen. Note that if PC-do-completion (qv) binds
    ;; completion-base-size to nil, then completion does not replace the
    ;; correct amount of text in such cases.
    ;;
    ;; Neither of these problems occur when using PC for filenames in the
    ;; minibuffer, because in that case PC-do-completion is called without
    ;; an explicit value for END, and so uses (point-max). This is fine for
    ;; a filename, because the end of the filename must be at the end of
    ;; the minibuffer. The same is not true for lisp symbols.
    ;;
    ;; [1] An alternate fix would be to not move point to the hyphen
    ;; in such cases, but that would make the behaviour different from
    ;; that for filenames. It seems PC moves point to the site of the
    ;; first difference between the possible completions.
    ;;
    ;; Alternatively alternatively, maybe end should be computed in
    ;; the same way as beg. That would change the behaviour though.
    (if (equal last-command 'PC-lisp-complete-symbol)
        (PC-do-completion nil beg PC-lisp-complete-end t)
      (if PC-lisp-complete-end
          (move-marker PC-lisp-complete-end end)
        (setq PC-lisp-complete-end (copy-marker end t)))
      (PC-do-completion nil beg end t))))

(defun PC-complete-as-file-name ()
   "Perform completion on file names preceding point.
 Environment vars are converted to their values."
   (interactive)
   (let* ((end (point))
          (beg (if (re-search-backward "[^\\][ \t\n\"\`\'][^ \t\n\"\`\']"
				       (point-min) t)
                   (+ (point) 2)
                   (point-min)))
          (minibuffer-completion-table 'PC-read-file-name-internal)
          (minibuffer-completion-predicate "")
          (PC-not-minibuffer t))
     (goto-char end)
     (PC-do-completion nil beg end)))

;; Facilities for loading C header files.  This is independent from the
;; main completion code.  See also the variable `PC-include-file-path'
;; at top of this file.

(defun PC-look-for-include-file ()
  (if (string-match "[\"<]\\([^\"<>]*\\)[\">]?$" (buffer-file-name))
      (let ((name (substring (buffer-file-name)
			     (match-beginning 1) (match-end 1)))
	    (punc (aref (buffer-file-name) (match-beginning 0)))
	    (path nil)
	    new-buf)
	(kill-buffer (current-buffer))
	(if (equal name "")
	    (with-current-buffer (car (buffer-list))
	      (save-excursion
		(beginning-of-line)
		(if (looking-at
		     "[ \t]*#[ \t]*include[ \t]+[<\"]\\(.+\\)[>\"][ \t]*[\n/]")
		    (setq name (buffer-substring (match-beginning 1)
						 (match-end 1))
			  punc (char-after (1- (match-beginning 1))))
		  ;; Suggested by Frank Siebenlist:
		  (if (or (looking-at
			   "[ \t]*([ \t]*load[ \t]+\"\\([^\"]+\\)\"")
			  (looking-at
			   "[ \t]*([ \t]*load-library[ \t]+\"\\([^\"]+\\)\"")
			  (looking-at
			   "[ \t]*([ \t]*require[ \t]+'\\([^\t )]+\\)[\t )]"))
		      (progn
			(setq name (buffer-substring (match-beginning 1)
						     (match-end 1))
			      punc ?\<
			      path load-path)
			(if (string-match "\\.elc$" name)
			    (setq name (substring name 0 -1))
			  (or (string-match "\\.el$" name)
			      (setq name (concat name ".el")))))
		    (error "Not on an #include line"))))))
	(or (string-match "\\.[[:alnum:]]+$" name)
	    (setq name (concat name ".h")))
	(if (eq punc ?\<)
	    (let ((path (or path (PC-include-file-path))))
	      (while (and path
			  (not (file-exists-p
				(concat (file-name-as-directory (car path))
					name))))
		(setq path (cdr path)))
	      (if path
		  (setq name (concat (file-name-as-directory (car path)) name))
		(error "No such include file: <%s>" name)))
	  (let ((dir (with-current-buffer (car (buffer-list))
		       default-directory)))
	    (if (file-exists-p (concat dir name))
		(setq name (concat dir name))
	      (error "No such include file: `%s'" name))))
	(setq new-buf (get-file-buffer name))
	(if new-buf
	    ;; no need to verify last-modified time for this!
	    (set-buffer new-buf)
	  (set-buffer (create-file-buffer name))
	  (erase-buffer)
	  (insert-file-contents name t))
	;; Returning non-nil with the new buffer current
	;; is sufficient to tell find-file to use it.
	t)
    nil))

(defun PC-include-file-path ()
  (or PC-include-file-path
      (let ((env (getenv "INCPATH"))
	    (path nil)
	    pos)
	(or env (error "No include file path specified"))
	(while (setq pos (string-match ":[^:]+$" env))
	  (setq path (cons (substring env (1+ pos)) path)
		env (substring env 0 pos)))
	path)))

;; This is adapted from lib-complete.el, by Mike Williams.
(defun PC-include-file-all-completions (file search-path &optional full)
  "Return all completions for FILE in any directory on SEARCH-PATH.
If optional third argument FULL is non-nil, returned pathnames should be
absolute rather than relative to some directory on the SEARCH-PATH."
  (setq search-path
	(mapcar (lambda (dir)
		  (if dir (file-name-as-directory dir) default-directory))
		search-path))
  (if (file-name-absolute-p file)
      ;; It's an absolute file name, so don't need search-path
      (progn
	(setq file (expand-file-name file))
	(file-name-all-completions
	 (file-name-nondirectory file) (file-name-directory file)))
    (let ((subdir (file-name-directory file))
	  (ndfile (file-name-nondirectory file))
	  file-lists)
      ;; Append subdirectory part to each element of search-path
      (if subdir
	  (setq search-path
		(mapcar (lambda (dir) (concat dir subdir))
			search-path)
		file ))
      ;; Make list of completions in each directory on search-path
      (while search-path
	(let* ((dir (car search-path))
	       (subdir (if full dir subdir)))
	  (if (file-directory-p dir)
	      (progn
		(setq file-lists
		      (cons
		       (mapcar (lambda (file) (concat subdir file))
			       (file-name-all-completions ndfile
							  (car search-path)))
		       file-lists))))
	  (setq search-path (cdr search-path))))
      ;; Compress out duplicates while building complete list (slloooow!)
      (let ((sorted (sort (apply 'nconc file-lists)
			  (lambda (x y) (not (string-lessp x y)))))
	    compressed)
	(while sorted
	  (if (equal (car sorted) (car compressed)) nil
	    (setq compressed (cons (car sorted) compressed)))
	  (setq sorted (cdr sorted)))
	compressed))))

(defun PC-read-file-name-internal (string dir action)
  "Extend `read-file-name-internal' to handle include files.
This is only used by "
  (if (string-match "<\\([^\"<>]*\\)>?\\'" string)
      (let* ((name (match-string 1 string))
	     (str2 (substring string (match-beginning 0)))
	     (completion-table
	      (mapcar (lambda (x)
                        (format (if (string-match "/\\'" x) "<%s" "<%s>") x))
		      (PC-include-file-all-completions
		       name (PC-include-file-path)))))
              (cond
               ((not completion-table) nil)
               ((eq action 'lambda) (test-completion str2 completion-table nil))
               ((eq action nil) (PC-try-completion str2 completion-table nil))
          ((eq action t) (all-completions str2 completion-table nil))))
    (read-file-name-internal string dir action)))


(provide 'complete)

;; arch-tag: fc7e2768-ff44-4e22-b579-4d825b968458
;;; complete.el ends here