time module

[cppforlife]

Describe the problem/challenge you have

even though ytt does not have access to current time, it's handy to be able to work with date/time formats. for example i'd like to parse two iso8601 timestamps, compare them or increment/decrement them.

Example of a timestamp i'd like to work with (from k8s): creationTimestamp: "2021-06-11T05:00:49Z" and want to be able to add/substract durations (as desribed by go's time.Duration)

Describe the solution you'd like

i think exposing time functionality as provided by go will be the easiest way to go about this. lets discuss the api for time module in this issue.

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[pivotaljohn]

Is this specifically about ytt templates being able to parse strings into time.Time?

Or are you thinking that this involves plumbing through https://yaml.org/type/timestamp.html . Meaning that if a timestamp is specified in say a Data Value (with the !!timestamp tag), it would populate in data.values as a Starlark wrapper for time.Time?

[pivotaljohn]

This is certainly in scope for what ytt aims to do. Reads like a valuable (if general) use-case. ==> "carvel accepted"

We're chatting about scope on this. ==> "discussion"

[cppforlife]

Is this specifically about ytt templates being able to parse strings into time.Time?

this. definitely not the other. also time.Duration.

[cari-lynn]

Looks like there is a time module in starlark-go. Since this was added recently and ytt is using a forked version of starlark we can take this as inspiration. It has

from_timestamp(sec, nsec)
is_valid_timezone(loc)
now()
parse_duration(d)
parseTime(x, format, location)
time(year, month, day, hour, minute, second, nanosecond, location)

With ytt being hermetic now() is not applicable. I could see a function like parseTime() as useful for supporting multiple time formats.

[aaronshurley]

Moving this to the Unprioritized Backlog for now. Sounds like this is something that would be beneficial but requires a little more design discussion. For now, it's not in our roadmap. Open for contributions.