Introduce flake dev pattern

[aldoborrero]

Right now if we run nix flake metadata, we obtain the following output:

Terminal outputs of Inputs

thinkpad-x1 :: Dev/nix-community/ethereum.nix2 ‹feat/devshell*› % nix flake metadata
Resolved URL:  git+file:///home/aldo/Dev/nix-community/ethereum.nix2
Locked URL:    git+file:///home/aldo/Dev/nix-community/ethereum.nix2?ref=refs%2fheads%2ffeat%2fdevshell&rev=21d7880e1e8c95b75209115c7b86c32c7985b714
Description:   A reproducible Nix package set for Ethereum clients and utilities
Path:          /nix/store/q2cn8xv7d4wvv1nrg16ngj57a6ai4jpn-source
Revision:      21d7880e1e8c95b75209115c7b86c32c7985b714
Revisions:     166
Last modified: 2023-04-28 10:27:16
Inputs:
├───devshell: github:numtide/devshell/3e0e60ab37cd0bf7ab59888f5c32499d851edb47
│   ├───flake-utils: github:numtide/flake-utils/846b2ae0fc4cc943637d3d1def4454213e203cba
│   └───nixpkgs follows input 'nixpkgs'
├───flake-compat: github:edolstra/flake-compat/35bb57c0c8d8b62bbfd284272c928ceb64ddbde9
├───flake-parts: github:hercules-ci/flake-parts/dcc36e45d054d7bb554c9cdab69093debd91a0b5
│   └───nixpkgs-lib follows input 'nixpkgs'
├───flake-root: github:srid/flake-root/f1c0b93d05bdbea6c011136ba1a135c80c5b326c
├───foundry-nix: github:shazow/foundry.nix/e3e0951e0cb668e7796f1fde2926ff32dc544d49
│   ├───flake-utils: github:numtide/flake-utils/3cecb5b042f7f209c56ffd8371b2711a290ec797
│   └───nixpkgs follows input 'nixpkgs'
├───hercules-ci-effects: github:hercules-ci/hercules-ci-effects/15ff4f63e5f28070391a5b09a82f6d5c6cc5c9d0
│   ├───flake-parts: github:hercules-ci/flake-parts/c13d60b89adea3dc20704c045ec4d50dd964d447
│   │   └───nixpkgs-lib: github:NixOS/nixpkgs/130fa0baaa2b93ec45523fdcde942f6844ee9f6e?dir=lib
│   ├───hercules-ci-agent: github:hercules-ci/hercules-ci-agent/0b90d1a87c117a5861785cb85833dd1c9df0b6ef
│   │   ├───flake-parts: github:hercules-ci/flake-parts/c13d60b89adea3dc20704c045ec4d50dd964d447
│   │   │   └───nixpkgs-lib follows input 'hercules-ci-effects/hercules-ci-agent/nixpkgs'
│   │   ├───haskell-flake: github:hercules-ci/haskell-flake/1e1660e6dd00838ba73bc7952e6e73be67da18d1
│   │   ├───nix-darwin: github:LnL7/nix-darwin/87b9d090ad39b25b2400029c64825fc2a8868943
│   │   │   └───nixpkgs follows input 'hercules-ci-effects/hercules-ci-agent/nixpkgs'
│   │   ├───nixpkgs: github:NixOS/nixpkgs/c90c4025bb6e0c4eaf438128a3b2640314b1c58d
│   │   └───pre-commit-hooks-nix: github:cachix/pre-commit-hooks.nix/1a20b9708962096ec2481eeb2ddca29ed747770a
│   │       ├───flake-compat: github:edolstra/flake-compat/35bb57c0c8d8b62bbfd284272c928ceb64ddbde9
│   │       ├───flake-utils: github:numtide/flake-utils/5aed5285a952e0b949eb3ba02c12fa4fcfef535f
│   │       ├───gitignore: github:hercules-ci/gitignore.nix/a20de23b925fd8264fd7fad6454652e142fd7f73
│   │       │   └───nixpkgs follows input 'hercules-ci-effects/hercules-ci-agent/pre-commit-hooks-nix/nixpkgs'
│   │       ├───nixpkgs follows input 'hercules-ci-effects/hercules-ci-agent/nixpkgs'
│   │       └───nixpkgs-stable: github:NixOS/nixpkgs/2f9fd351ec37f5d479556cd48be4ca340da59b8f
│   └───nixpkgs: github:NixOS/nixpkgs/1544ef240132d4357d9a39a40c8e6afd1678b052
├───nixpkgs: github:nixos/nixpkgs/4d2b37a84fad1091b9de401eb450aae66f1a741e
├───nixpkgs-unstable: github:nixos/nixpkgs/2362848adf8def2866fabbffc50462e929d7fffb
└───treefmt-nix: github:numtide/treefmt-nix/b25d1a3c2c7554d0462ab1dfddf2f13128638b90
    └───nixpkgs follows input 'nixpkgs'

As we can see from the above output, we export a big amount of inputs derivation that consumers of ethereum.nix doesn't necessarily need, exploding their flake.lock dependencies. Inputs like hercules-ci-effects, treefmt-nix are only internal for development purposes.

We can do better. Speaking with @zimbatm he proposed I should use what he called the flake dev pattern. The idea is quite simplistic:

• Create another flake for dev purposes with all the current inputs we have.
• Load that flake with direnv directly.
• Leave the existing flake with only the necessary inputs needed for consumers but nothing else.

I have proof of concept made on this branch, but a separate PR will be added soon once #257 is merged back to main branch.

This is the issue that introduces this concept natively inside Nix.

[aldoborrero]

I'll mark this issue as closed for now. We can always get back to the idea if it makes sense.