tpl: Add "cached" piped option

[bep]

See #3042

The partialCached template func name makes for a bad API.

It would be nice if we could say:

{{ partial "head.html" . | cache }}
{{ partial "head.html" . | cache "some-key" }}

We would keep the old func as an alias, and this keyword would only work for the partial func at the start, but one could imagine we could use it for other things, and maybe add more "options" later.

I guess this would only work for funcs with "vararg room" on the end.

[bep]

/cc @moorereason @digitalcraftsman

[digitalcraftsman]

In other words: the partialCached func could become more generic in the sense that it could also cache / handle more things than just templates in the future, right?

[bep]

No, turn it around: It is the cache keyword that is the generic part (one could imagine partial doing other stuff too, but that is not on my mind in this scenario).

[digitalcraftsman]

No, turn it around: It is the cache keyword that is the generic part

So, cache becomes the more generic version of partialCached?

[bep]

So, cache becomes the more generic version of partialCached?

Yes. Maybe not relevant for partial, but for, say, images, one could imagine piping several "action options"; image | rotate 30 | flip...?

But even in the partial case, it makes a cleaner API.

[digitalcraftsman]

images, one could imagine piping several "action options"; image | rotate 30 | flip...?

Do you want to cache a composition of template functions this way?

[bep]

No.

[bep]

And the slightly longer version is:

I would love to come up with a generic "cache func" (how-to-suggestion welcome), but this is just options sent into another func (which can be accumulated).

So both of these are the same:

• partialCached "head.html"
• partial | cached

The reason we added the partialCached variant was because func Partial(name string, cached bool) is kind of hard to use and document as a template func. And it becomes even worse if you get func Partial(name string, cached, pretty bool).

Then you may end up with:

• partialPrettyCached "head.html"

And this breaks down fast if you need some additional and optional cache key etc. So:

• partial "head.html" | pretty | cached "home-page"

And please don't ask me what pretty is -- I just made it up, but it is a configuration option and not a function doing the work.

[moorereason]

I agree and understand the reasoning, but the proposed implementation doesn't make sense. With

partial "head.html" . | cached

the partial will always be executed. cached needs to control execution, so the pipe usage would be rare, I think.

[bep]

proposed implementation doesn't make sense.

I haven't proposed an implementation, just the API.

[bep]

But this isn't really important. Let it linger.

[github-actions]

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