[PATCH 4 of 5 V2] revset: use delayregistrar to register predicate in extension easily

[Yuya Nishihara]

On Sat, 02 Jan 2016 01:28:28 +0900, FUJIWARA Katsunori wrote:
> At Fri, 1 Jan 2016 17:53:10 +0900,
> Yuya Nishihara wrote:
> > "cmdtable" was wrong?
> > 
> > I like consistent extension APIs, so my idea was something like this:
> > 
> > 1. define table of revset symbols per extension
> > 
> >   # creates new table and associated decorator
> >   revsetpredicate = registrar.revsetpredicate()
> 
> In this case, loading logic looks inside 'revsetpredicate' object to
> get predicate functions to be loaded, doesn't it ? (= table-ness of
> bridging object isn't important)

Right. The difference is who controls the loading logic.

  (a) @command          mercurial.dispatch loads cmdtable
  (b) @revsetpredicate  hgext.xxx updates revset.symbols

We haven't (a) for revsets and templates, and your patch follows it,
which is straightforward. I just wondered if (a) is preferable as an extension
API.

> >   revsetpredicate = registrar.revsetpredicate(revsetsymbols)
> 
> (BTW, would you also mean that revset decorator specific code should
> be placed in registrar.py by sample code above ? I think that it
> shouldn't so, IMHO)

Yes. If the registrar provides all decorators, an extension can avoid
importing templatekw or templatefilters just because it defines new template
keywords/filters. (though the revset module would be necessary to define new
workable revset predicates.)

> > 2. load them by dispatch._dispatch()
> 
> What about registration steps below, if explicit setup() on
> revsetpredicate isn't suitable for consistent API ? This can prevents
> dispatch (and registrar) from depending on revset, template XXXX, and
> so on.
>
>   dispatch._dispatch()
>   - extensions.loadall()
>     - at loading extension
>       - instantiate revset.predicate or so as 'revsetpredicate' (*1)
>         - at loading revset.py
>           - register revset specific hook (*2) to registrar.py
>       - revset.predicate()
>         - decorator stores information internally
>     - uisetup of extension
>     - extsetup of extension
>   - invoke hooks registered in registrar.py on each extensions
>     - invoke hook (*2)
>       - load predicates from 'revsetpredicate' attribute (*1) of extension

registrar shouldn't import revset, but I think it's fine for dispatch to
import revset. And import-time hook registration won't be necessary.

Regards,