bug#33380: 27.0.50; Emacs hangs in current-time-zone

bug#33380: 27.0.50; Emacs hangs in current-time-zone

[Sam Steingold]

In GNU Emacs 27.0.50 (build 1, x86_64-apple-darwin17.7.0, NS
appkit-1561.60 Version 10.13.6 (Build 17G3025))
 of 2018-11-12 built on C-6111-SSTEINGO
Repository revision: db711687c3983eda60275dadcc4dc75119e6c0ae
Repository branch: master
Windowing system distributor 'Apple', version 10.3.1561
System Description:  Mac OS X 10.13.6

When I hit `d` in Calendar, Emacs hangs, and debug-on-quit reveals the
backtrace:

Debugger entered--Lisp error: (quit)
  current-time-zone(-242240400)
  calendar-next-time-zone-transition((-3852 1873))
  calendar-dst-find-data((-3852 1873))
  calendar-dst-find-startend(1962)
  calendar-dst-starts(1962)
  eval((calendar-dst-starts year))
  dst-in-effect(716571.289583333)
  dst-adjust-time((11 27 1962) 6.94794218501546)
  solar-sunrise-sunset((11 27 1962))
  solar-sunrise-sunset-string((11 27 1962))
  diary-sunrise-sunset()
  eval((diary-sunrise-sunset))
  diary-sexp-entry("(diary-sunrise-sunset)" "" (11 27 1962))
  diary-list-sexp-entries((11 27 1962))
  diary-list-entries((11 27 1962) 1)
  diary-view-entries(1)
  funcall-interactively(diary-view-entries 1)
  call-interactively(diary-view-entries nil nil)
  command-execute(diary-view-entries)

this does not happen with "current" dates.


-- 
Sam Steingold <http://sds.podval.org> <http://www.childpsy.net>
<http://steingoldpsychology.com>

bug#33380: 27.0.50; Emacs hangs in current-time-zone

[Glenn Morris]

Sam Steingold wrote:

> When I hit `d` in Calendar, Emacs hangs,

A smaller example is to evaluate: (calendar-dst-starts 1962)

Bisection points to 93fe420942c08111a6048af7c4d7807c61d80a09,
"New (TICKS . HZ) timestamp format".

bug#33380: 27.0.50; Emacs hangs in current-time-zone

[Paul Eggert]

[-- Attachment #1: Type: text/plain, Size: 297 bytes --]

On 11/14/18 10:49 AM, Glenn Morris wrote:
> A smaller example is to evaluate: (calendar-dst-starts 1962)

Thanks for the smaller example. I installed the attached patch into 
master to fix that and am optimistically marking this bug as done. And 
thanks, Sam, for reporting the original problem.


[-- Attachment #2: 0001-Fix-probing-for-pre-1970-DST.patch --]
[-- Type: text/x-patch, Size: 1087 bytes --]

From 917fe0d0383eabf621f59a7314882423bc12f74a Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@Penguin.CS.UCLA.EDU>
Date: Wed, 14 Nov 2018 11:42:59 -0800
Subject: [PATCH] Fix probing for pre-1970 DST

* lisp/calendar/cal-dst.el (calendar-next-time-zone-transition):
Fix recently-introduced rounding bug when probing for DST
transitions before 1970 (Bug#33380).
---
 lisp/calendar/cal-dst.el | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lisp/calendar/cal-dst.el b/lisp/calendar/cal-dst.el
index 25264bda09..8392e81b16 100644
--- a/lisp/calendar/cal-dst.el
+++ b/lisp/calendar/cal-dst.el
@@ -154,7 +154,7 @@ calendar-next-time-zone-transition
        (while
            ;; Set PROBE to halfway between LO and HI, rounding down.
            ;; If PROBE equals LO, we are done.
-           (not (= lo (setq probe (/ (+ lo hi) 2))))
+           (not (= lo (setq probe (floor (+ lo hi) 2))))
          ;; Set either LO or HI to PROBE, depending on probe results.
          (if (eq (car (current-time-zone probe)) hi-utc-diff)
              (setq hi probe)
-- 
2.19.1