Proof of concept: Template context function

[wxiaoguang]

cc @yardenshoham for #24342

This is a proof of concept of the "template context function".

Now in templates we only need to do:

Locale: {{CtxLocale "home"}}<br>
DateTime: {{CtxDateTime "full" "2001-02-03"}}<br>

TODO:

1. Refactor the 500 page rendering
2. Design better name/struct for CtxFunc

[delvh]

Phew, I don't really know if I like the proposed approach.
That will cause some nasty import problems, as Go doesn't allow import cycles, and modules/context is pretty much our backbone package…
This means for example that we cannot add any function located inside models or services that needs a context…
I mean, we can circumvent this with offering modular functions, i.e.

type Context {
  …
  loadUser func(ctx Context, <remaining params>)
}

func (ctx *Context) loadUser(<remaining params>) {
  loadUser(ctx, <remaining params>)
}

but that doesn't scale well and is a lot of overhead code to write…

[wxiaoguang]

That will cause some nasty import problems, as Go doesn't allow import cycles, and modules/context is pretty much our backbone package…

"import", no worry, the framework can handle them correctly later.

[silverwind]

Design better name/struct for CtxFunc

I guess we can keep the same names, e.g. Locale. The refactor will be massive in changed lines count, but other than that, trivial via sed/perl replacement 😉

[silverwind]

Should we merge this POC?

[wxiaoguang]

Nope, it's far from complete. It needs #24461 and maybe some other PRs before merging.

[delvh]

Still blocked?

[wxiaoguang]

Not blocked by code but blocked by my limited time 😭

[wxiaoguang]

Golang team make some progress

text/template, html/template: add ExecuteFuncs https://go-review.googlesource.com/c/go/+/510738

I think the official "context function" support will be available soon.

[wxiaoguang]

Wait for the Golang official solution