[ruby-core:91359] [Ruby trunk Bug#15340] Time.local behaving inconsistently for excess days after 2038

Issue #15340 has been updated by usa (Usaku NAKAMURA).

Backport changed from 2.3: WONTFIX, 2.4: REQUIRED, 2.5: DONE to 2.3: WONTFIX, 2.4: DONE, 2.5: DONE

ruby_2_4 r66967 merged revision(s) 65974.

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Bug #15340: Time.local behaving inconsistently for excess days after 2038
https://bugs.ruby-lang.org/issues/15340#change-76612

* Author: dmikurube (Dai MIKURUBE)
* Status: Closed
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 2.4.1, 2.5.1
* Backport: 2.3: WONTFIX, 2.4: DONE, 2.5: DONE
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Time.local accepts a day of month that exceeds the largest day of the month, for example, 2018-02-31. The behavior looks inconsistent before v.s. after 2038. Are they expected behavior?

The behavior looks somewhat reasonable before 2037. The number of exceeding days is passed on the next month. 2018-02-31 exceeds for 3 days since 2018-02-28. 2018-02-31 is recognized as 2018-03-03.

But after 2038, the behavior looks strange and inconsistent compared to before 2038, as shown in the example below observed in Ruby 2.4.1 and 2.5.1.

The difference looks affecting Time.strptime as well.

~~~ ruby
irb(main):001:0> ENV['TZ']=nil
=> nil

irb(main):002:0> Time.local(2037,2,28,0,0,0,0)
=> 2037-02-28 00:00:00 +0900
irb(main):003:0> Time.local(2037,2,29,0,0,0,0)
=> 2037-03-01 00:00:00 +0900
irb(main):004:0> Time.local(2037,2,30,0,0,0,0)
=> 2037-03-02 00:00:00 +0900
irb(main):005:0> Time.local(2037,2,31,0,0,0,0)
=> 2037-03-03 00:00:00 +0900

irb(main):006:0> Time.local(2038,2,28,0,0,0,0)
=> 2038-02-28 00:00:00 +0900
irb(main):007:0> Time.local(2038,2,29,0,0,0,0)
=> 2038-03-01 00:00:00 +0900
irb(main):008:0> Time.local(2038,2,30,0,0,0,0)
=> 2038-02-28 00:00:00 +0900
irb(main):009:0> Time.local(2038,2,31,0,0,0,0)
=> 2038-03-01 00:00:00 +0900

irb(main):010:0> ENV['TZ']='UTC'
=> "UTC"

irb(main):011:0> Time.local(2037,2,28,0,0,0,0)
=> 2037-02-28 00:00:00 +0000
irb(main):012:0> Time.local(2037,2,29,0,0,0,0)
=> 2037-03-01 00:00:00 +0000
irb(main):013:0> Time.local(2037,2,30,0,0,0,0)
=> 2037-03-02 00:00:00 +0000
irb(main):014:0> Time.local(2037,2,31,0,0,0,0)
=> 2037-03-03 00:00:00 +0000

irb(main):015:0> Time.local(2038,2,28,0,0,0,0)
=> 2038-02-28 00:00:00 +0000
irb(main):016:0> Time.local(2038,2,29,0,0,0,0)
=> 2038-03-01 00:00:00 +0000
irb(main):017:0> Time.local(2038,2,30,0,0,0,0)
=> 2038-02-28 00:00:00 +0000
irb(main):018:0> Time.local(2038,2,31,0,0,0,0)
=> 2038-03-01 00:00:00 +0000
~~~

JFYI: I thought I observed a case 2038-02-30 is recognized as 2038-03-01 when ENV['TZ']=nil, but just now I couldn't reproduce the case. It might be my mistake in operations, but let me leave the log just in case. (It might be because I was in different timezones when I observed them. The example above was in JST, and the below was in PST.)

~~~ ruby
irb(main):001:0> ENV['TZ']=nil
=> nil

irb(main):002:0> Time.local(2037,2,30,0,0,0,0)
=> 2037-03-02 00:00:00 -0800
irb(main):003:0> Time.local(2038,2,30,0,0,0,0)
=> 2038-03-01 00:00:00 -0800
~~~




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