[ruby-core:121810] [Ruby Bug#21301] Invalid Dates Accepted When Using "UTC" in Time.new

Issue #21301 has been updated by mame (Yusuke Endoh).


Thanks. Actually, the same issue also occurs with a value of 60 for seconds:

```ruby
Time.new(2025, 1, 1, 0, 0, 60, "UTC")    #=> 2025-01-01 00:00:60 UTC   # invalid
Time.new(2025, 1, 1, 0, 0, 60, "+00:00") #=> 2025-01-01 00:01:00 +0000
```

Note that 60 seconds can be valid in the case of a leap second.

```ruby
Time.new(2016, 12, 31, 23, 59, 60, "UTC")    #=> 2016-12-31 23:59:60 UTC   # can be valid
Time.new(2016, 12, 31, 23, 59, 60, "+00:00") #=> 2016-12-31 23:59:60 +0000
```

`2016-12-31 23:59:60 UTC` is valid if the system has leap second data.

----------------------------------------
Bug #21301: Invalid Dates Accepted When Using "UTC" in Time.new
https://bugs.ruby-lang.org/issues/21301#change-112871

* Author: mame (Yusuke Endoh)
* Status: Open
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
2025-04-31 does not exist, but, when creating a time object with the "UTC" zone, the value is accepted without error:

```ruby
Time.new(2025, 4, 31, 0, 0, 0, "UTC") #=> expected: 2025-05-01 00:00:00 UTC
                                      #=> actual:   2025-04-31 00:00:00 UTC
```

In contrast, using the "+00:00" time zone works as expected and rolls the date over to 2025-05-01:

```ruby
Time.new(2025, 4, 31, 0, 0, 0, "+00:00") # => 2025-05-01 00:00:00 +0000
```

Note that 2025-04-30T24:00:00Z is correctly rolled over to 2025-05-01T00:00:00Z.
And 2025-04-31T24:00:00Z is rolled over to 2025-04-01!

```ruby
Time.new(2025, 4, 30, 24, 0, 0, "UTC") #=> 2025-05-01 00:00:00 UTC # OK
Time.new(2025, 4, 31, 24, 0, 0, "UTC") #=> 2025-04-01 00:00:00 UTC # What?
```



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