[HELP]: Share your .nix usage propose about nix-env-selector HOT 5 OPEN

{
  	inputs = {
		utils.url = "github:numtide/flake-utils";
		naersk.url = "github:nmattia/naersk";
		fenix.url = "github:nix-community/fenix";
  	};

  	outputs = { self, nixpkgs, utils, naersk, fenix }:
	utils.lib.eachDefaultSystem (system: let
		pkgs = nixpkgs.legacyPackages."${system}";
		# Specify Rust Toolchain
		# Use Stable (Default)
		# naersk-lib = naersk.lib."${system}";
		# Use Nightly (provided by fenix)
		naersk-lib = naersk.lib."${system}".override {
			# Use Fenix to get nightly rust
			inherit (fenix.packages.${system}.minimal) cargo rustc;
		};
	in rec {
		# `nix build`
		packages.nixman = naersk-lib.buildPackage {
			pname = "nixman";
			root = ./.;
			nativeBuildInputs = with pkgs; [
				pkg-config
			];
			buildInputs = with pkgs; [
				ncurses
				openssl
			];
		};
		defaultPackage = packages.nixman;

		# `nix run`
		apps.nixman = utils.lib.mkApp {
			drv = packages.nixman;
		};
		defaultApp = apps.nixman;

		# `nix develop`
		devShell = pkgs.mkShell {
			nativeBuildInputs = packages.nixman.nativeBuildInputs;
			buildInputs = packages.nixman.buildInputs;
		};
	});
}

let
  # pin nixpkgs to a particular commit
  nixpkgsRev = "e924a8823325472a42c06bb519cc59d4c8bda614";
  # a nix function to fetch a tar ball from github
  githubTarball = owner: repo: rev:
    builtins.fetchTarball { url = "https://github.com/${owner}/${repo}/archive/${rev}.tar.gz"; };

  # import set of packages from nixpkgs github repo at a particular revision with the config specified below
  pkgs = import (githubTarball "nixos" "nixpkgs" nixpkgsRev) { };
in
{
  inherit pkgs;
  shell = pkgs.mkShell {
    name = "elm-dev";
    buildInputs = [
      pkgs.elmPackages.elm
      pkgs.elmPackages.elm-format
      pkgs.elmPackages.elm-test
      pkgs.nodejs-15_x
    ];
    shellHook = ''
      echo "start using elm"
    '';
  };
}

let
  nixpkgsRev = "1d55adbce8af68fee04f42b562f5376be5a6026c";
  githubTarball = owner: repo: rev:
    builtins.fetchTarball { url = "https://github.com/${owner}/${repo}/archive/${rev}.tar.gz"; };
  pkgs = import (githubTarball "nixos" "nixpkgs" nixpkgsRev) { };
in
with pkgs;{
  shell = mkShell {
    name = "dev env";
    buildInputs = [
      nodejs-10_x
      (yarn.override { nodejs = nodejs-10_x; })
      libpng12
    ];
    LD_LIBRARY_PATH="${pkgs.libpng12}/lib";
    shellHook = ''
      echo "Start working";
      echo "Run yarn serve to run the app";
    '';
  };
}

{
  description = "Package build for gstreamer project";
  inputs.haskellNix.url = "github:input-output-hk/haskell.nix";
  inputs.nixpkgs.follows = "haskellNix/nixpkgs-unstable";
  inputs.flake-utils.url = "github:numtide/flake-utils";
  outputs = { self, haskellNix, nixpkgs, flake-utils }: 
    flake-utils.lib.eachSystem [ "x86_64-linux" "x86_64-darwin" ] (system:
    let
      overlays = [ haskellNix.overlay
        (final: prev: {
          # This overlay adds our project to pkgs
          streamlineProject =
            final.haskell-nix.project' {
              src = ./.;
              compiler-nix-name = "ghc8104";
              # projectFileName = "stack.yaml";
              modules = [{
              # Replace `extra-libraries` dependencies
                packages.cuda.components.library.libs = pkgs.lib.mkForce 
                  [ pkgs.cudatoolkit_10_2 ];
                packages.cuda.components.library.pkgconfig = pkgs.lib.mkForce 
                 [ [ pkgs.cudatoolkit_10_2 ] ];
              }];
            };
          # Maps haskell library names to nixpkgs library names
          "gstreamer-1.0" = pkgs.gst_all_1.gstreamer;
          "gstreamer-plugins-bad-1.0" = pkgs.gst_all_1.gst-plugins-bad;
          "gstreamer-plugins-good-1.0" = pkgs.gst_all_1.gst-plugins-good;
          "gstreamer-plugins-base-1.0" = pkgs.gst_all_1.gst-plugins-base;
          cuda = prev.cudatoolkit_10_2;
        })
      ];
      pkgs = import nixpkgs { inherit system overlays; config.allowUnfree = true; };
      flake = pkgs.streamlineProject.flake {};
      in flake // {
        # Built by `nix build .`
        defaultPackage = flake.packages."streamline:exe:streamline";

        # This is used by `nix develop .` to open a shell for use with
        # `cabal`, `hlint` and `haskell-language-server`
        devShell = pkgs.streamlineProject.shellFor {
          tools = {
            cabal = "latest";
            ghcid = "latest";
            hlint = "latest";
            haskell-language-server = "latest";
          };
        };
      });
}

{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    nixCargoIntegration = {
      url = "github:yusdacra/nix-cargo-integration";
      inputs.nixpkgs.follows = "nixpkgs";
    };
    flakeCompat = {
      url = "github:edolstra/flake-compat";
      flake = false;
    };
  };

  outputs = inputs: inputs.nixCargoIntegration.lib.makeOutputs {
    root = ./.;
    buildPlatform = "crate2nix";
    overrides = {
      shell = common: prev: {
        packages = prev.packages ++ [ common.pkgs.musl.dev ];
        commands = prev.commands ++ [
          {
            name = "generate-cert";
            command = ''
              mkcert localhost 127.0.0.1 ::1
              mv localhost+2.pem cert.pem
              mv localhost+2-key.pem key.pem
            '';
          }
          {
            name = "run-with-console";
            command = ''RUSTFLAGS="--cfg tokio_unstable" cargo r --features console'';
          }
        ];
      };
    };
  };
}