dependencies added via cabal-flags are missing

[shivaraj-bh]

cryptostore has a cabal-flag to use crypton instead of cryptonite, see: https://github.com/ocheron/cryptostore/blob/1c52dd5fc7c0184cfae0e09e305bef54a04854a4/cryptostore.cabal#L68-L71. But when when the cabal-flag is enabled using settings.cryptostore.cabalFlags.use_crypton = true;, cryptostore fails to build with missing dependencies.

Reproducer:

nix develop github:shivaraj-bh/cryptostore-use-crypton

I am thinking this is an upstream bug where cabal2nix generates a derivation before enabling/disabling cabal-flags?