Name: dev-flake
Rating: 92
Author: AddG0

When to Use

•Setting up a new project's dev environment
•Adding local services (PostgreSQL, Redis, Kafka) to an existing flake
•Fixing or modernizing a project's Nix dev shell

Required Files

code

project/
├── flake.nix
├── flake.lock   # auto-generated
└── .envrc       # always just: use flake

flake.nix Template

nix

{
  description = "Project Name";

  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-25.11";
    flake-parts = {
      url = "github:hercules-ci/flake-parts";
      inputs.nixpkgs-lib.follows = "nixpkgs";
    };
    git-hooks-nix = {
      url = "github:cachix/git-hooks.nix";
      inputs.nixpkgs.follows = "nixpkgs";
    };
    process-compose-flake.url = "github:Platonic-Systems/process-compose-flake";
    services-flake.url = "github:juspay/services-flake";
  };

  outputs = inputs @ {flake-parts, ...}:
    flake-parts.lib.mkFlake {inherit inputs;} {
      systems = ["x86_64-linux" "aarch64-linux" "aarch64-darwin" "x86_64-darwin"];

      imports = [
        inputs.git-hooks-nix.flakeModule
        inputs.process-compose-flake.flakeModule
      ];

      perSystem = {pkgs, config, ...}: let
        # Override language toolchains here
        java = pkgs.jdk21;
        gradle = pkgs.gradle.override {inherit java;};
      in {
        # Local services: `nix run .#services`
        process-compose."services" = {
          imports = [inputs.services-flake.processComposeModules.default];
          settings.processes = {
            pg.shutdown.timeout_seconds = 5;
            redis.shutdown.timeout_seconds = 5;
          };
          services = {
            postgres."pg" = {
              enable = true;
              port = 5432;
              listen_addresses = "127.0.0.1";
              initialDatabases = [{name = "mydb";}];
            };
            redis."redis" = {
              enable = true;
              port = 6379;
              bind = "127.0.0.1";
            };
          };
        };

        pre-commit.settings.hooks = {
          alejandra.enable = true;  # always
          # google-java-format.enable = true;  # Java projects
          # prettier.enable = true;             # JS/TS projects
        };

        devShells.default = pkgs.mkShell {
          inherit (config.pre-commit.devShell) shellHook;
          packages = with pkgs; [
            # Add project-specific tools here
          ];
        };
      };
    };
}

Conventions

•Pin nixpkgs to a release branch (e.g., nixos-25.11)
•follows nixpkgs on inputs that support it to reduce closure size
•Shutdown timeouts on all process-compose services to prevent hangs
•All tools via Nix — no global installs, no wrapper scripts (e.g., use gradle not ./gradlew)
•Omit process-compose-flake and services-flake inputs if no local services needed

Commands

Command	Purpose
`direnv allow`	Enable environment (one-time)
`nix develop`	Enter dev shell manually
`nix run .#services`	Start local services
`nix flake update`	Update all inputs
`nix flake lock --update-input <name>`	Update single input

Language References

When the project uses a specific language ecosystem, load the corresponding reference for inputs, patterns, and conventions:

•For Python projects using uv (pyproject.toml + uv.lock), see references/uv2nix.md

Steps

•Ask what language/framework and what local services are needed
•Scaffold flake.nix from the base template, trimming unused sections
•If a language reference exists, load it and merge those inputs/patterns into the flake
•Add language-specific packages to devShells.default.packages
•Add appropriate pre-commit hooks for the language
•Configure services if needed, otherwise remove process-compose inputs
•Create .envrc with use flake
•Run nix flake lock to generate the lock file