Fix code comment

[codebien]

Add the Sum stat into the resolvers map. It is helpful for reusing the same function from the Remote Write output. grafana/xk6-output-prometheus-remote#64

Just fix a comment

[na--]

Hmm 🤔 if I am reading this correctly:

k6/cmd/options.go

Lines 191 to 200 in 616e5e2

	if flags.Changed("summary-trend-stats") {
	trendStats, errSts := flags.GetStringSlice("summary-trend-stats")
	if errSts != nil {
	return opts, errSts
	}
	if _, errSts = metrics.GetResolversForTrendColumns(trendStats); err != nil {
	return opts, errSts
	}
	opts.SummaryTrendStats = trendStats
	}

Then changing this function will also allow users to specify k6 run --summary-trend-stats min,med,max,sum, which is not something we want, right? 🤔

Why do you need this change?

[codebien]

which is not something we want, right?

@na-- I thought we were fine adding it, it isn't included in the default values but it allows users to generate that stat if needed.

Why do you need this change?

The Prometheus Output has the option for exporting the sum stat, so it would be helpful to reuse the same function to have it supported from the k6's resolver. The k6 function is useful because it has the validation / parsing already implemented for the percentile. If it is possible then I would avoid to clone the same logic in the Output.

[na--]

I am not sure how the sum of a Trend's values would be useful in any way for the end-of-test summary? Maybe it could be of use in some weird handleSummary() use case? 🤔 Even so, AFAIK, nobody has requested something like this so far.

Also, the sum is easy to get with our current TrendSink implementation, since it doesn't require any calculation - we update it on every value add() call. However, if we adopt HDR histograms (#763), calculating the sum would require some computation and even so, it will be just an approximation.

So, given the dubious value to users and the potential complication for HDR histograms, I think copying some code to the extension (with a TODO) would be preferable to hastily updating the values in this k6 function.

[codebien]

Ok, then I think I can do something hacky for excluding the sum from the validation and still reuse the k6 function. Thanks for your opinion 🙇

[na--]

The fix to the metrics.Time comments were good though 😅