Is this still true after Don't copy flakes to the store unnecessarily (maybe 3rd time's the charm) by xokdvium · Pull Request #15711 · NixOS/nix · GitHub (included in 2.35.0)?
They are lazily downloaded even before 2.35.0
I think I’m holding the fast version wrong, what’s going wrong here?
ulucs@MacBookPro:~/ > nix build github:fzakaria/nixpkgs-multiverse#legacyPackages.x86_64-linux.fast."967d40bec14b".python3
error:
… while calling the 'throw' builtin
at «github:fzakaria/nixpkgs-multiverse/4745826df4b3d554ea546d8a428767b790dd19da»/multiverse.nix:660:19:
659| # drvPath a fake cannot have, so the message says what to append.
660| drvPath = throw ''
| ^
661| multiverse: ${drvName} is a fast fake derivation and has no drvPath — it
error: multiverse: python3-3.8.9 is a fast fake derivation and has no drvPath — it
substitutes by store path alone. Append the output: …python3."3.8.9".out
(outputs: out).
For override / nix develop / a real derivation, use .eval instead.
Ah, I had to manually target .out