From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.org!.POSTED!not-for-mail From: Pip Cet Newsgroups: gmane.emacs.bugs Subject: bug#33414: 27.0.50; inhibit-changing-match-data can be t in syntax-propertize functions, breaking backtrace and looking-at Date: Sat, 17 Nov 2018 13:30:04 +0000 Message-ID: NNTP-Posting-Host: blaine.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" X-Trace: blaine.gmane.org 1542461343 7512 195.159.176.226 (17 Nov 2018 13:29:03 GMT) X-Complaints-To: usenet@blaine.gmane.org NNTP-Posting-Date: Sat, 17 Nov 2018 13:29:03 +0000 (UTC) To: 33414@debbugs.gnu.org Original-X-From: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane.org@gnu.org Sat Nov 17 14:28:59 2018 Return-path: Envelope-to: geb-bug-gnu-emacs@m.gmane.org Original-Received: from lists.gnu.org ([208.118.235.17]) by blaine.gmane.org with esmtp (Exim 4.84_2) (envelope-from ) id 1gO0eh-0001nZ-5L for geb-bug-gnu-emacs@m.gmane.org; Sat, 17 Nov 2018 14:28:59 +0100 Original-Received: from localhost ([::1]:49360 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gO0gn-0005ky-BA for geb-bug-gnu-emacs@m.gmane.org; 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X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.6.x X-BeenThere: debbugs-submit@debbugs.gnu.org X-Mailman-Version: 2.1.18 Precedence: list X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 208.118.235.43 X-BeenThere: bug-gnu-emacs@gnu.org List-Id: "Bug reports for GNU Emacs, the Swiss army knife of text editors" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: bug-gnu-emacs-bounces+geb-bug-gnu-emacs=m.gmane.org@gnu.org Original-Sender: "bug-gnu-emacs" Xref: news.gmane.org gmane.emacs.bugs:152470 Archived-At: I'm debugging an issue in a custom mode that happened because my syntax-propertize function, which is complex, assumed it could use the match data and looking-at. However, the function itself was called from within looking-at-p, via a regexp generated by (regexp-opt "..." 'symbols), so inhibit-changing-match-data was still bound to t, yielding unexpected results. This was a bit tricky to debug because (backtrace) doesn't work when inhibit-changing-match-data is t. (In emacs -Q, enter (let ((inhibit-changing-match-data t)) (backtrace)) into the *scratch* buffer and evaluate with C-M-x.) At the very least, we should document these unfortunate limitations, though I think it would be better to remove them.