Issue #11595 has been updated by Andrew Vit.


Careful: not every time with offset 0 is UTC. 

A time zone with offset +0100/-0100 may have DST rules, and should not be `utc?`.

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Bug #11595: Time#utc? and Time#gmt? return misleading results based on $TZ
https://bugs.ruby-lang.org/issues/11595#change-56549

* Author: David Celis
* Status: Open
* Priority: Normal
* Assignee: Akira Tanaka
* ruby -v: ruby 2.2.3p173 (2015-08-18 revision 51636) [x86_64-darwin14]
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN
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There is an issue with Time#utc? and its alias, Time#gmt?, that return misleading results based on the value of the TZ environment variable. It seems that the only way for a Time instance to return `true` for `utc?` is if you explicitly call `#utc` on it before:

~~~
ENV['TZ'] = 'UTC'
# => "UTC"
time = Time.now
# => 2015-10-14 19:30:00 +0000
time.utc?
# => false
time = time.utc
# => 2015-10-14 19:30:00 UTC
time.utc?
# => true
~~~

This seems misleading based on the value of $TZ being "UTC". The expected result for calling `Time.now.utc?` in this case would be `true`, as would that be expected for time zones that are considered links to "UTC" based on the [tzdata list](https://en.wikipedia.org/wiki/List_of_tz_database_time_zones). These include "UTC", "GMT", "Etc/UTC", "Etc/GMT", "Universal", etc.

---Files--------------------------------
time_utc.patch (927 Bytes)


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