[ruby-core:62121] [ruby-trunk - Bug #9764] Date and DateTime strptime and strftime not supporting proper Week Numbering for Monday vs Sunday as start day and %G causes ignore of all other format arguments

Issue #9764 has been updated by Steve R.


@Tadayoshi funaba,

I think i understand part of the issue now related to some of the confusion.

Date.Comercial() allows you to provide the Year and Week number to get a date.  It was the expectation that `puts Date.strptime('2014 00', '%Y %U' )` would generate the same value as .Comercial but with Sunday as the first day of Week.

Is there a way to support .Commercial input arguments with a Sunday first day or week?

The use case is that many systems will return a %U style 0-53 week time grouping (group results by week number).  The system returns a Week Number integer and a Year integer.  You want to convert this into a date for sorting and other benefits, but you do not know the day number.

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Bug #9764: Date and DateTime strptime and strftime not supporting proper Week Numbering for Monday vs Sunday as start day and %G causes ignore of all other format arguments
https://bugs.ruby-lang.org/issues/9764#change-46279

* Author: Steve R
* Status: Rejected
* Priority: Low
* Assignee: tadayoshi funaba
* Category: 
* Target version: 
* ruby -v: ruby 2.0.0p247 (2013-06-27 revision 41674) [x86_64-darwin12.4.0]
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN
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Date and DateTime strftime and strptime are not supporting %U (0-53 Week Numbers as defined in strptime): 
http://www.ruby-doc.org/stdlib-2.1.1/libdoc/date/rdoc/Date.html#method-i-strftime

Some examples that are not producing expected results/output:

1. require 'date'; puts Date.new(2013,12,30).strftime("%G %U")  # 2014 52  -- How is this Week 52 of 2013??

2. require 'date'; puts Date.strptime("2014 01","%G %U")  # 2013-12-30 -- This should really be 2013-12-29 as the 29th is the sunday and the 30th is the Monday, and %U should be using Sunday as the first day of week.

3. The following three examples all produce the same result but really should not.  Even if you change the week number to any number it still stays at the same output/result.  It seems like there is a bug related to %G that ignores all other commands:

puts Date.strptime('00 2014', '%U %G')  # 2013-12-30
puts Date.strptime('00 2014', '%W %G')  # 2013-12-30
puts Date.strptime('2014W011', '%GW%V%u')  # 2013-12-30


Additionally one would expect the following two lines to produce the same results:
puts Date.strptime('00 2014', '%W %G')  # 2013-12-30
puts Date.strptime('00 2014', '%W %Y')  # Invalid Date Argument





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