[Nix-dev] Re: warning if trying to install a package but it fails an assert.

[Andres Loeh]

Yes, I agree that the default for subversion should be *with*
perl bindings.

In general, as Marc explained as well, there's indeed no problem
to the "check if the requirements are met by the defaults" scheme,
though. I'll try to explain it conceptually, not based on passthru:

Currently, we're mostly passing complete derivations (let's say,
because I like types, of type DERIVATION) into the Nix
expressions for individual packages. These have a fixed set of
options hard-wired at the time they're passed. Instead of doing
that, let's pass the actual function, of type
(OPTIONS -> DERIVATION) plus a set of default options (of type
OPTIONS). The individual package can then decide whether to just
go with the default options (by applying the function to the
options), or if to modify the options before applying.

Cheers,
  Andres