tpl/debug: Add debug.Timer

[bep]

Closes #11580

[jmooring]

Oh wow. And you can pass it around in context. Nice.

{{ $t := debug.Timer "TestSeq" }}
{{ partial "foo.html" (dict "page" . "timer" $t) }}

[bep]

Oh wow. And you can pass it around in context. Nice.

I don't see how useful that would be in its current form:

• The names are global and only the first .Stop will have an effect.
• The timers are only created and logged if log level is <= INFO
• The timings gets printed sorted with the slowest last (which I find helpful)

Does the above make sense?
Also, does the debug.Timer naming make sense? I thought about putting it in the time package, but I changed my mind.

[jmooring]

I agree this should live in the debug package.

My thought on starting the timer in template A and stopping in template B was about following the chain with a single page site, but the --templateMetrics --templateMetricsHints flags already provide the important information, and the result is statistically meaningul (pages > 1).

It did make me think about page-attached timers though, which I suppose we can already do by stuffing time.Now into a scratch.

[bep]

It did make me think about page-attached timers though, which I suppose we can already do by stuffing time.Now into a scratch.

Then I'd just put a timer at the top of single.html and stop it at the end, but I don't think that is particulary useful. The typically use case for this is to pinpoint performance bottle necks. I used this yesterday to easily identify a "hot loop" where I did way too much work, and shaved 70% off the build time.

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