Re: Parameterized packages

[Tobias Geerinckx-Rice]

Ludo',

Ludovic Courtès wrote:
> While thinking about <https://issues.guix.info/issue/35671> and 
> looking
> for ways to allow users to install just the locales they need 
> right from
> ‘guix package’, I realized that “parameterized packages” are a
> low-hanging fruit

Wow.  Unexpected turn…

I'm still thinking about this, so all this is just me doing it out 
loud:

>   (package
>     (inherit glibc-utf8-locales)
>     (properties `((locales . ("zh_CN.utf8")))))
>
> and tadaam! we have a parameterized package.
>
> There’s a couple of gotchas:
>
>   • We’d need to store more info in manifest entries so that
>     transformation options are preserved upon ‘guix upgrade’.
>
>   • We might need to expose the package parameters somehow, so 
>   that if
>     one types ‘--with-argument=foobar=baz’, they get a correct 
>     error
>     message saying that “foobar” is not a known parameter.

Interesting idea to piggy-back on the properties field, and it 
might save some code (at least initially), but I don't see the 
overlap here.

None of the current properties (superseded, upstream-name, 
*-variant, cpe-name, hidden?) make much sense to expose in this 
way; they're semimmutable facts about the package.

While a dedicated field can provide richer metadata, such as 
description, basic ‘types’ & sane/permitted values, to be used by 
the UI.

Looking at Exherbo/ntoo, this will inevitably lead to factoring 
out very common option metadata so one doesn't have to keep 
writing ‘x11 bool "Add support for the X Window System"’ in 
every. single. package.

Then come the people asking how to set CFLAGS for all packages and 
you'll know you've made it.

>   • We might want to make the CLI option less verbose too, but 
>   how?

Possibly relevant: do you see package options¹ being added to 
package specifications?  That seems to be the classical approach.

Kind regards,

T G-R

[1]: I use the term ‘option’ because it's what my last FHS 
distribution called them, and it was a good distribution, and 
because ‘arguments’ is already an unrelated field in package 
expressions, and flags are boolean, but substitute whatever name 
you prefer.

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