(regexp-opt-depth "[\\(]") => 1 :-(

[Alan Mackenzie]

There Is No Alternative:  regexp-opt-depth MUST analyse its argument
properly.  The following rewrite of regexp-opt-depth does just that.

[Well, OK, it would be as well for somebody else to check the formulation
of regexp-opt-not-groupie*-re.  ;-]

The patch below passes the following test cases:
(regexp-opt-depth "(asdf)")             => 0
(regexp-opt-depth "\\(asdf\\)")         => 1
(regexp-opt-depth "\\(\\(asdf\\)\\)")   => 2
(regexp-opt-depth "\\(?:asdf\\)")       => 0
(regexp-opt-depth "[\\(]")              => 0

(regexp-opt-depth "[a]\\(]asd\\)")      => 1
(regexp-opt-depth "[^a]\\(]asd\\)")     => 1
(regexp-opt-depth "[]\\(]asd)")         => 0
(regexp-opt-depth "[^]\\(]asd)")        => 0
(regexp-opt-depth "\\(? \\)")           signals "invalid regexp".

*************************************************************************
*** regexp-opt.1.24.el  Fri Apr 18 18:34:34 2003
--- regexp-opt.acm.1.24.el      Sun Apr 20 22:05:33 2003
***************
*** 110,115 ****
--- 110,124 ----
           (re (regexp-opt-group sorted-strings open)))
        (if words (concat "\\<" re "\\>") re))))
  
+ (defconst regexp-opt-not-groupie*-re
+   (let ((harmless-ch "[^\\\\[]")
+         (esc-pair-not-lp "\\\\[^(]")
+         (class "\\[^?]?[^]]*]")
+         (shy-lp "\\\\(\\?:"))
+     (concat "\\(" harmless-ch "\\|" esc-pair-not-lp
+             "\\|" class "\\|" shy-lp "\\)*"))
+   "Matches any part of a regular expression EXCEPT for non-shy \"\\\\(\"s")
+ 
  ;;;###autoload
  (defun regexp-opt-depth (regexp)
    "Return the depth of REGEXP.
***************
*** 120,130 ****
      (string-match regexp "")
      ;; Count the number of open parentheses in REGEXP.
      (let ((count 0) start)
!       (while (string-match "\\(\\`\\|[^\\]\\)\\\\\\(\\\\\\\\\\)*([^?]"
!                          regexp start)
!       (setq count (1+ count)
!             ;; Go back 2 chars (one for [^?] and one for [^\\]).
!             start (- (match-end 0) 2)))
        count)))
  
  ;;; Workhorse functions.
--- 129,141 ----
      (string-match regexp "")
      ;; Count the number of open parentheses in REGEXP.
      (let ((count 0) start)
!       (while
!           (progn
!             (string-match regexp-opt-not-groupie*-re regexp start)
!             (setq start (match-end 0))
!             (< start (1- (length regexp))))
!         (setq count (1+ count)
!               start (+ start 2)))        ; step START over "\\("
        count)))
  
  ;;; Workhorse functions.
*************************************************************************

-- 
Alan Mackenzie (Munich, Germany)