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bug#35264: "Match data clobbered by buffer modification hooks" when hook
From: |
Noam Postavsky |
Subject: |
bug#35264: "Match data clobbered by buffer modification hooks" when hooks only shifted match-data's markers |
Date: |
Sun, 14 Apr 2019 00:40:13 -0400 |
Version: 27.0.50 26.2 25.3
X-Debbugs-CC: Stefan Monnier <monnier@iro.umontreal.ca>
emacs -Q -l bug-xxxx-match-data-marker-clobber.el
Hit <f12>, gives
Debugger entered--Lisp error: (error "Match data clobbered by buffer
modification hooks")
replace-match("ABCDEF" t t)
(let* ((after-change-functions (list (function (lambda (&rest _) (let (...
...) (save-excursion ...))))))) (search-backward "abcdef") (replace-match
"ABCDEF" t t))
(save-current-buffer (set-buffer (get-buffer-create "*test*"))
(display-buffer (current-buffer)) (erase-buffer) (insert "1234567890\n")
(insert "abcdefghilk\n") (make-local-variable (quote after-change-functions))
(let* ((after-change-functions (list (function (lambda (&rest _) (let ...
...)))))) (search-backward "abcdef") (replace-match "ABCDEF" t t)))
bug-match-data-marker-clobber()
funcall-interactively(bug-match-data-marker-clobber)
call-interactively(bug-match-data-marker-clobber nil nil)
command-execute(bug-match-data-marker-clobber)
But the modification hook in question did call save-match-data. As far
as I can tell, the problem is that the match-data consists of markers,
whose position gets shifted by deletion of characters. The check for
this error uses simple integers, so there's no way it can account for
this.
I think this is a variant of Bug#23917, there was some talk there about
removing the check, perhaps that is the right solution.
DEFUN ("replace-match", Freplace_match, Sreplace_match, 1, 5, 0,
[...]
/* The functions below modify the buffer, so they could trigger
various modification hooks (see signal_before_change and
signal_after_change). If these hooks clobber the match data we
error out since otherwise this will result in confusing bugs. */
ptrdiff_t sub_start = search_regs.start[sub];
ptrdiff_t sub_end = search_regs.end[sub];
unsigned num_regs = search_regs.num_regs;
newpoint = search_regs.start[sub] + SCHARS (newtext);
/* Replace the old text with the new in the cleanest possible way. */
replace_range (search_regs.start[sub], search_regs.end[sub],
newtext, 1, 0, 1, 1);
[...]
if (search_regs.start[sub] != sub_start
|| search_regs.end[sub] != sub_end
|| search_regs.num_regs != num_regs)
error ("Match data clobbered by buffer modification hooks");
bug-xxxx-match-data-marker-clobber.el:
(defun bug-match-data-marker-clobber ()
(interactive)
(with-current-buffer (get-buffer-create "*test*")
(display-buffer (current-buffer))
(erase-buffer)
(insert "1234567890\n")
(insert "abcdefghilk\n")
(make-local-variable 'after-change-functions)
(let* ((after-change-functions `
(,(lambda (&rest _)
(let ((inhibit-modification-hooks nil)
(after-change-functions nil))
(save-excursion
(save-match-data
(goto-char (point-min))
(looking-at "[0-9]")
(delete-char 1))
;; match-data is restored, but markers have a
;; different position now, because of the
;; deletion.
;;
;; (match-data) ;=> (#<marker@11> #<marker@17>)
))))))
(search-backward "abcdef")
;; (match-data) ;=> (#<marker@12> #<marker@18>)
(replace-match "ABCDEF" t t) ;; Triggers `after-change-functions'.
)))
(setq debug-on-error t)
(define-key global-map [f12] 'bug-match-data-marker-clobber)
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- bug#35264: "Match data clobbered by buffer modification hooks" when hooks only shifted match-data's markers,
Noam Postavsky <=