emacsWithPackages should know its package set

[peti]

The emacsWithPackages function expects as an argument the list of packages to include in the environment. Now, this means that both emacsWithPackages and the Emacs package set used to construct its argument refers to an Emacs binary, but they don't necessarily refer to the same. This can have weird effects, i.e. suppose that I'd like to have an environment with the Emacs variant that doesn't depend on X11:

(emacsWithPackages.override { emacs = emacs24-nox; }) [ ??? ];

Obviously, I'd like to pass a list of packages from a package set that''s build with emacs24-nox, too, but such a package set doesn't exist and there's no easy way for me to create one. emacsPackagesGen is a recursive function, so I cannot call it in place without a let binding, which is very inconvenient. Furthermore, what happens when I accidentally pass packages to the function above that are, say, compiled with Emacs 23.x? IMHO, the interface shouldn't require its users to deal with that kind of mess.

I would suggest that emacsWithPackages becomes a function that lives inside of the Emacs package set and that takes as an argument a function that maps from an Emacs package set (the one emacsWithPackages lives in) to a list of packages. With that API, I could simply write

(emacsWithPackages.override { emacs = emacs24-nox; }) (ps: [ ps.bbdb ];

and get the expected result without any fuss.

Cc: @ttuegel

[ttuegel]

I plan to do this after I merge emacsPackages and emacsPackagesNg. If we did this now, it wouldn't be possible to use packages from both sets, which is still necessary at the moment.

[peti]

If we did this now, it wouldn't be possible to use packages from both sets, which is still necessary at the moment.

Why do you think it's impossible to include packages from other sets in the list argument?

[ttuegel]

I guess it's possible, but doesn't that defeat the purpose of making the interface less messy?

[ttuegel]

Sorry, that sounds unintentionally combative. I mean, if this would be helpful to you, I'm happy to do it now because I had planned to do it anyway.

[peti]

No worries. I have my own little helper function in config.nix that does what I want, so I'm not dependent on that change being made quickly. Just feel free to progress with this stuff at your own pace; I didn't mean to come across as if I'm trying to rush things.

[peti]

Related issues where other people had the same problem: #10811 and #11004.