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(434) strptime_with_mock_date :: Fix year boundary #437

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(434) strptime_with_mock_date :: Fix year boundary #437

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2a5e87c
strptime_with_mock_date :: Fix year boundary
jchapa Jan 3, 2025
73ef98e
minor nits
jchapa Jan 3, 2025
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9 changes: 7 additions & 2 deletions lib/timecop/time_extensions.rb
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Expand Up @@ -50,7 +50,12 @@ def strptime_with_mock_date(str = '-4712-01-01', fmt = '%F', start = Date::ITALY

d = Date._strptime(str, fmt)
now = Time.now.to_date
year = d[:year] || d[:cwyear] || now.year

# If "current" time falls near a year boundary, with a year-ambiguous str, we need to explicitly handle it
cwday = d[:cwday] && (now.to_date + (d[:cwday] - now.to_date.wday))
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the to_date calls on now are not necessary. it will be easier to read without those.

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nice catch

wday = d[:wday] && (now.to_date + (d[:wday] - now.to_date.wday))

year = d[:year] || d[:cwyear] || (cwday || wday || now).year
mon = d[:mon] || now.mon
if d.keys == [:year]
Date.new(year, 1, 1, start)
Expand All @@ -59,7 +64,7 @@ def strptime_with_mock_date(str = '-4712-01-01', fmt = '%F', start = Date::ITALY
elsif d[:yday]
Date.new(year, 1, 1, start).next_day(d[:yday] - 1)
elsif d[:cwyear] || d[:cweek] || d[:wnum0] || d[:wnum1] || d[:wday] || d[:cwday]
week = d[:cweek] || d[:wnum1] || d[:wnum0] || now.strftime('%W').to_i
week = d[:cweek] || d[:wnum1] || d[:wnum0] || (cwday || wday || now).strftime('%W').to_i
if d[:wnum0] #Week of year where week starts on sunday
if d[:cwday] #monday based day of week
Date.strptime_without_mock_date("#{year} #{week} #{d[:cwday]}", '%Y %U %u', start)
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36 changes: 36 additions & 0 deletions test/date_strptime_year_boundary_scenarios.rb
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@@ -0,0 +1,36 @@
module DateStrptimeYearBoundaryScenarios
#calling freeze and travel tests are making the date Time.local(1992,1,1)

# Test for wday
def test_date_strptime_year_boundary_with_day_of_week
assert_equal Date.strptime('Thursday', '%A'), Date.new(1992, 1, 2)
assert_equal Date.strptime('Monday', '%A'), Date.new(1991, 12, 30)
end

# Test for cwday
def test_date_strptime_year_boundary_with_iso_day_of_week
assert_equal Date.strptime('4', '%u'), Date.new(1992, 1, 2)
assert_equal Date.strptime('1', '%u'), Date.new(1991, 12, 30)
end

# Test for wnum1
def test_date_strptime_year_boundary_with_wnum1
assert_equal Date.strptime('52', '%W'), Date.new(1992, 12, 28)
assert_equal Date.strptime('1', '%W'), Date.new(1992, 01, 6)
end

# Test for wnum0
def test_date_strptime_year_boundary_with_wnum0
assert_equal Date.strptime('52', '%U'), Date.new(1992, 12, 27)
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Date.new(1992,12,27) is sort of a magic number, I had to do research to understand why it was the right date. What do you think of using Date.strptime('1992-52', '%Y-%U') instead of newing up that date? This comment is general to all the magic dates in here.

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BTW if you implement this idea then for the cweek tests you have to use %G not %Y like Date.strptime('1992-52', '%G-%V'). I spent a bit of time scratching my head at this

3.2.2 :016 > Date.strptime('1992-53', '%Y-%V')
 => #<Date: 1992-01-01 ((2448623j,0s,0n),+0s,2299161j)>

before i realized that the iso8601 commercial week has its own year concept too.

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Date.new(1992,12,27) is sort of a magic number, I had to do research to understand why it was the right date. What do you think of using Date.strptime('1992-52', '%Y-%U') instead of newing up that date? This comment is general to all the magic dates in here.

I like this idea. 2 caveats:

  • We would lose some coverage if we compared the output of this function to another output of this function. e.g. what if a future change breaks how the year is computed more broadly in strptime which impacts both sides of the assertion? In that scenario, we'd be blind to other types of changes. we could cover those with addl tests, but I think there's some advantage to using explicit constants in these tests.
  • We use magic numbers in our other strptime tests. We could update these though, but would also introduce the same risk.

For these specific tests, if I don't change the other strptime tests, then I think we could safely improve readability making the change you suggested.

assert_equal Date.strptime('1', '%U'), Date.new(1992, 01, 5)
end

# Test for cweek
def test_date_strptime_year_boundary_with_cweek
# TODO: year-ambiguous cweek is not handled correctly during year boundaries:
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i do not understand this TODO.

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@jchapa jchapa Jan 6, 2025 •
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I think you referenced this in your other comment, but I think in general we're just not handling cweek well in this library. I'm not sure if that's something we want to tackle in this PR.

Some examples (from master branch):

irb(main):003> Date.strptime('1992-52', '%G-%V')
=> #<Date: 1992-12-28 ((2448985j,0s,0n),+0s,2299161j)>
irb(main):004> Date.strptime_without_mock_date('1992-52', '%G-%V')
=> #<Date: 1992-12-21 ((2448978j,0s,0n),+0s,2299161j)>

irb(main):001> Date.strptime('52', '%V')
=> #<Date: 2025-12-29 ((2461039j,0s,0n),+0s,2299161j)>
irb(main):002> Date.strptime_without_mock_date('52', '%V')
=> #<Date: 2025-12-22 ((2461032j,0s,0n),+0s,2299161j)>

Going to poke at this a little more and hopefully find a cleaner solve

# assert_equal Date.strptime('52', '%V'), Date.new(1992, 12, 21)
# assert_equal Date.strptime('53', '%V'), Date.new(1991, 12, 28)
assert_equal Date.strptime('52', '%V'), Date.new(1992, 12, 28)
assert_equal Date.strptime('1', '%V'), Date.new(1992, 01, 6)
end
end
17 changes: 17 additions & 0 deletions test/timecop_date_strptime_freeze_year_boundary_test.rb
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require_relative "test_helper"
require 'timecop'
require_relative 'date_strptime_year_boundary_scenarios'

class TestTimecop < Minitest::Test
def setup
t = Time.local(1992,1,1)
Timecop.freeze(t)
end

def teardown
Timecop.return
end

# Test for Date
include DateStrptimeYearBoundaryScenarios
end
18 changes: 18 additions & 0 deletions test/timecop_date_strptime_travel_year_boundary_test.rb
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require_relative "test_helper"
require 'timecop'
require_relative 'date_strptime_year_boundary_scenarios'

class TestTimecop < Minitest::Test
def setup
t = Time.local(1992,1,1)
Timecop.travel(t)
end

def teardown
Timecop.return
end

# Test for Date
include DateStrptimeYearBoundaryScenarios

end
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