Daylight Savings not handled properly

[bricker]

Daylight savings "falls back" in the states on November 4th, 2012, at exactly 2am. It goes backwards and repeats the 1am hour.

Time.new(2012, 11, 4, 0)
# => 2012-11-04 00:00:00 -0700

Chronic.parse("2012-11-04 at 12am")
# => 2012-11-04 01:00:00 -0700

Chronic.parse("2012-11-04")
# => 2012-11-04 11:00:00 -0800 

Those first two dates should return the same, and I would expect the last one to return 12pm. Hopefully this is a silly mistake I'm making, or there is a reasonable explanation. DST is a nightmare!

[travisbell]

Probably related, this morning, my Chronic calls started straight up failing right at 2AM when DST kicked over.

Chronic.parse('tomorrow at 4:00 pm')

Is now nil. Argh?

1.9.2p320 :006 > Chronic.parse('tomorrow at 4:00 pm')
 => nil 
1.9.2p320 :007 > 

I'm currently setting the timezone like so, if that matters:

Time.zone = "Pacific Time (US & Canada)"
Chronic.time_class = Time.zone

Setting the timezone to 'UTC' seems to fix it. But I am wondering why this worked all the way until yesterday but not today?

[markerdmann]

I ran into the exact same issue today described by @travisbell above.

[wakiki]

I also encountered the same error as @bricker - has there been any updates on this?

[leejarvis]

No there hasn't, I'm struggling to find time for Chronic at the moment. Hoping to start hitting some of these as soon as possible

[markerdmann]

@injekt I have some time to work on this. I'll fork and send a pull request if I have any luck. Do you have an idea of where in the codebase I might start looking to find the source of the bug?

[wakiki]

I don't know if this is the same issue but I noted the following in issue #179

1.9.3p362 :021 > Time.current
=> Tue, 12 Mar 2013 11:01:30 GMT +00:00
1.9.3p362 :017 > Time.zone = "London"
=> "London"
1.9.3p362 :018 > Chronic.time_class = Time.zone
=> (GMT+00:00) London
1.9.3p362 :019 > Chronic.parse("April 1st at 9am")
=> Mon, 01 Apr 2013 09:00:00 BST +01:00
1.9.3p362 :020 > Chronic.parse("20 days from now at 9am")
=> Mon, 01 Apr 2013 10:00:00 BST +01:00

Interestingly, specifying "April 1st" works fine whereas "20 days from now" doesn't work.

Chronic 0.9.1
Rails 3.2.6

[leejarvis]

@markerdmann sorry I hadn't noticed your message until today. I can't reproduce the original issue so it'll probably take me a little longer to fix. Usually I would enable debug mode (Chronic.debug = true) then jump into the method that handles this sequence (in Handlers) then debug things from there. It's not always a quick process and there's a few subtle bugs in Chronic that aren't easy to fix. I do still have a rewrite that's currently in progress but again I'm finding it hard to find work on this at the moment, everything is tied up with work

[stanhu]

We ran into this in floraison/et-orbi#23 as well. I think these lines are questionable:

chronic/lib/chronic/repeaters/repeater_time.rb

Lines 81 to 96 in 2b1eae7

	yesterday_midnight = midnight - full_day
	tomorrow_midnight = midnight + full_day
	offset_fix = midnight.gmt_offset - tomorrow_midnight.gmt_offset
	tomorrow_midnight += offset_fix
	catch :done do
	if pointer == :future
	if @type.ambiguous?
	[midnight + @type.time + offset_fix, midnight + half_day + @type.time + offset_fix, tomorrow_midnight + @type.time].each do |t|
	(@current_time = t; throw :done) if t >= @now
	end
	else
	[midnight + @type.time + offset_fix, tomorrow_midnight + @type.time].each do |t|
	(@current_time = t; throw :done) if t >= @now
	end

Try passing in Chronic.parse('2020-11-01 00:00:00') on a system that has daylight savings:

Time.parse('2020-11-01 00:00:00')
=> 2020-11-01 00:00:00 -0700
Chronic.parse('2020-11-01 00:00:00')
=> 2020-11-01 01:00:00 -0700

Why did Chronic advance an hour like that?

When a date like this is passed in Chronic.parse, offset_fix becomes 3600 (1 hour), and the starting time advances by an hour.

If I try to get rid of this offset_fix:

diff --git a/lib/chronic/repeaters/repeater_time.rb b/lib/chronic/repeaters/repeater_time.rb
index 0a496e7..208553e 100644
--- a/lib/chronic/repeaters/repeater_time.rb
+++ b/lib/chronic/repeaters/repeater_time.rb
@@ -87,21 +87,21 @@ module Chronic
         catch :done do
           if pointer == :future
             if @type.ambiguous?
-              [midnight + @type.time + offset_fix, midnight + half_day + @type.time + offset_fix, tomorrow_midnight + @type.time].each do |t|
+              [midnight + @type.time, midnight + half_day + @type.time + offset_fix, tomorrow_midnight + @type.time].each do |t|
                 (@current_time = t; throw :done) if t >= @now
               end
             else
-              [midnight + @type.time + offset_fix, tomorrow_midnight + @type.time].each do |t|
+              [midnight + @type.time, tomorrow_midnight + @type.time].each do |t|
                 (@current_time = t; throw :done) if t >= @now
               end
             end
           else # pointer == :past
             if @type.ambiguous?
-              [midnight + half_day + @type.time + offset_fix, midnight + @type.time + offset_fix, yesterday_midnight + @type.time + half_day].each do |t|
+              [midnight + half_day + @type.time, midnight + @type.time + offset_fix, yesterday_midnight + @type.time + half_day].each do |t|
                 (@current_time = t; throw :done) if t <= @now
               end
             else
-              [midnight + @type.time + offset_fix, yesterday_midnight + @type.time].each do |t|
+              [midnight + @type.time, yesterday_midnight + @type.time].each do |t|
                 (@current_time = t; throw :done) if t <= @now
               end
             end

Tests like the following fail:

chronic/test/test_daylight_savings.rb

Lines 38 to 41 in 2b1eae7

	# ambiguous - resolve to this morning
	t = Chronic::RepeaterTime.new('900')
	t.start = @begin_daylight_savings
	assert_equal Time.local(2008, 3, 9, 9), t.next(:future).begin

.