`0 % <ActiveSupport::Duration>` returns unexpected result

[moveson]

Steps to reproduce

From the Rails console:
>> a = 0 % 1.second
>> a
#>

Expected behavior

a should report its existence as 0.

Actual behavior

a returns nothing at all: No 0, no nil, no indication of what it is. However,

>> a.zero?
#> true

System configuration

Rails version: 5.1.4

Ruby version: 2.3.5

[georgeclaghorn]

It returns an ActiveSupport::Duration with no parts:

> a = 0 % 1.second


> a.class
ActiveSupport::Duration

> a.parts
{}

ActiveSupport::Duration#inspect returns an empty string when the receiving object has no parts. Tricky!

[moveson]

That's interesting, and good to understand. But it does violate principle of least surprise.

>> a = 3 % 2
#> 1
>> a = 3 % 1
#> 0
>> a = 3 % 2.seconds
#> 1.0 second
>> a = 3 % 1.second
#> # Not 0 seconds? 

Note also that 0.seconds can be represented:

>> a = 0.seconds
#> 0 seconds

[kinnrot]

Looks like the problem is within ActiveSupport::Duration.build(0) compared to ActiveSupport::Duration.seconds(0)

build method reject all zero values, Maybe it should not reject the smallest unit, seconds.

You can also see that 'to_s' will return "0" and inspect returns the empty string because parts is empty