`nix-has-flakes` fails on later releases

[aameen-tulip]

`nix-has-flakes` fails on later releases

[aameen-tulip]

Nevermind this has already been fixed; it's just not on MELPA yet.

[aameen-tulip]

Alright, so there's still an issue here, even on master; I'm not sure if they've changed the enum values over time, but 1 ( used on master ) is associated with impure-derivations for me at 2.8. For me 2 was the value required for flakes, and 3 is also required in order to get nix show-config to work at all.

Here's the enums we care about for later releases on Nix ( this was tested on 2.8 and 2.9pre ):

/* nix/src/libutil/experimental-features.cc */
std::map<ExperimentalFeature, std::string> stringifiedXpFeatures = {
  /* 0 */  { Xp::CaDerivations, "ca-derivations" },
  /* 1 */  { Xp::ImpureDerivations, "impure-derivations" },
  /* 2 */  { Xp::Flakes, "flakes" },
  /* 3 */  { Xp::NixCommand, "nix-command" },
  /* 4 */  { Xp::RecursiveNix, "recursive-nix" },
  /* 5 */  { Xp::NoUrlLiterals, "no-url-literals" },
  /* 6 */  { Xp::FetchClosure, "fetch-closure" },
};

The following sanity checks also work:

$ nix --option experimental-features 'nix-command' show-config --json  \
     |jq '.["experimental-features"].value[]';
3
$ nix --option experimental-features 'flakes nix-command' show-config --json  \
     |jq '.["experimental-features"].value[]';
2
3