template: adding toTime function to TemplateExpander

[jrkt]

This PR adds a formatTime function in the TemplateExpander. As it stands now, the way to get the current time of a PromQL execution is to do something like this: {{ query "time()" | first | value || humanizeTime }}. This works great but only allows one format of time to be expressed. I'm proposing a simple function that does virtually the exact same thing as humanizeTime except that it allows you to pass in the format you expect to get back like this: {{ query "time()" | first | value || formatTime "2006-01-02 15:04:05" }}

[dgl]

Thanks, I think it would be better to instead add a "toTime" function that takes a unix epoch time and can convert it to a time.Time, that way other methods are available. (Formatting would look something like {{ (query "time()" | first | value | toTime).Format("...") }})

(This is similar to what is possible in alertmanager, e.g. prometheus/alertmanager#1188 (comment))

[jrkt]

I can do that.

[jrkt]

@dgl done.

[roidelapluie]

Thanks!

• Can you please add tests?
• Can you please document this?
• We could extract this logic to a convertToTime function, used in humanizeTimestamp and toTime

[jrkt]

@roidelapluie I have separated out the pieces of the functions that I could. I had to leave convertToFloat out of the shared function since the converted float is used in an error case in humanizeTimestamp. Everything else has been broken out though. I also added tests and updated the documentation. I added a new "Time" section to the documentation since there are now two functions directly related to time. Let me know if I missed anything.

[jrkt]

@roidelapluie is there anything I missed here?

[jrkt]

@roidelapluie requests resolved.

[roidelapluie]

Thanks!