Add nix flakes support (#594)

* flake.nix: add basic support

* Use flake-compat to derive default.nix & shell.nix from flake.nix

- introduce flake-compat
- pin nixpkgs at flake.lock
- modify how we import default.nix/shell.nix

* Move pinned nixpkgs from dep/nixpkgs to flake.lock

* CI: now build and test with nix flake as well

* Up ver to 1.9.17.1

.github/workflows/ci.yaml

@@ -13,7 +13,10 @@ jobs:
       DOCKERTAG: latest
     steps:
       - uses: actions/checkout@v2
-      - uses: cachix/install-nix-action@v12
+      - uses: cachix/install-nix-action@v13
+        with:
+          extra_nix_config: |
+            experimental-features = nix-command flakes
       # This also runs nix-build.
       - uses: cachix/cachix-action@v8
         with:
@@ -25,7 +28,13 @@ jobs:
       - name: Build 🔧
         run: |
           nix-build -j4 --no-out-link ci.nix
+          # Test default.nix
           nix-build -j4
+          # Test flake.nix
+          nix build --out-link flake-result
+      - name: Verify output of default.nix & flake.nix
+        run: |
+          [ $(readlink result) = $(readlink flake-result) ]
       - name: Retrieve neuron version
         run: |
           echo "NEURONVER=$(./result/bin/neuron --version)" >> $GITHUB_ENV

.gitignore

@@ -3,6 +3,7 @@ dist-*
 .ghc.environment.*
 result
 result-2
+result-data
 .shake
 .neuron
 neuron.prof

ci.nix

@@ -1,11 +1,11 @@
 { system ? builtins.currentSystem }:
 let
-  pkgs = import ./dep/nixpkgs { inherit system; };
+  pkgs = import ./nixpkgs.nix { inherit system; };
 in
 pkgs.recurseIntoAttrs {
   # Build both default.nix and shell.nix such that both derivations are
   # pushed to cachix. This allows the development workflow (bin/run, etc.) to
   # use cachix to full extent.
-  neuron = import ./default.nix {};
-  neuronShell = import ./shell.nix {};
+  neuron = import ./default.nix;
+  neuronShell = import ./shell.nix;
 }

default.nix

@@ -1,4 +1,13 @@
-args@{ system ? builtins.currentSystem, ...}:
-let 
-  pkgs = import ./dep/nixpkgs { inherit system; } ;
-in (import ./project.nix { pkgs = pkgs; } ).neuron
+(import
+  (
+    let
+      lock = builtins.fromJSON (builtins.readFile ./flake.lock);
+    in
+    fetchTarball {
+      url = "https://github.com/edolstra/flake-compat/archive/${lock.nodes.flake-compat.locked.rev}.tar.gz";
+      sha256 = lock.nodes.flake-compat.locked.narHash;
+    }
+  )
+  {
+    src = ./.;
+  }).defaultNix

docker.nix

@@ -7,8 +7,8 @@
 #       --argstr tag <image-tag>
 #   )
 let
-  pkgs = import ./dep/nixpkgs {};
-  neuron = import ./. {};
+  pkgs = import ./nixpkgs.nix {};
+  neuron = import ./.;
 in {
   name ? "sridca/neuron"
 , tag ? "dev"

flake.nix

@@ -0,0 +1,28 @@
+{
+  description = "Future-proof note-taking and publishing based on Zettelkasten";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/fcab19deb78fbb5ea24e19b133cf34358176396a";
+    flake-utils.url = "github:numtide/flake-utils";
+    flake-compat = {
+      url = "github:edolstra/flake-compat";
+      flake = false;
+    };
+  };
+
+  outputs = { self, nixpkgs, flake-utils, ... }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = import nixpkgs { inherit system; };
+        project = import ./project.nix { inherit pkgs; };
+
+      in rec {
+        packages = { neuron = project.neuron; };
+        defaultPackage = packages.neuron;
+
+        apps = { neuron = flake-utils.lib.mkApp { drv = packages.neuron; }; };
+        defaultApp = apps.neuron;
+
+        devShell = project.shell;
+      });
+}

neuron.cabal

@@ -1,6 +1,6 @@
 cabal-version: 2.4
 name: neuron
-version: 1.9.27.0
+version: 1.9.27.1
 license: AGPL-3.0-only
 copyright: 2020 Sridhar Ratnakumar
 maintainer: srid@srid.ca

nixpkgs.nix

@@ -0,0 +1,8 @@
+let
+  lock = builtins.fromJSON (builtins.readFile ./flake.lock);
+  nixpkgs = lock.nodes.nixpkgs.locked;
+
+in import (fetchTarball {
+  url = "https://github.com/nixos/nixpkgs/archive/${nixpkgs.rev}.tar.gz";
+  sha256 = nixpkgs.narHash;
+})

project.nix

@@ -1,5 +1,5 @@
 let
-  nixpkgs = import ./dep/nixpkgs {};
+  nixpkgs = import ./nixpkgs.nix {};
 in {
   pkgs ? nixpkgs,
   pkgsForBins ? null,

shell.nix

@@ -1 +1,13 @@
-args@{ ... }: (import ./project.nix args).shell
+(import
+  (
+    let
+      lock = builtins.fromJSON (builtins.readFile ./flake.lock);
+    in
+    fetchTarball {
+      url = "https://github.com/edolstra/flake-compat/archive/${lock.nodes.flake-compat.locked.rev}.tar.gz";
+      sha256 = lock.nodes.flake-compat.locked.narHash;
+    }
+  )
+  {
+    src = ./.;
+  }).shellNix

static.nix

@@ -1,7 +1,7 @@
 args@{...}:
 let 
   # FIXME: Use a nixpkgs that works with static builds
-  nixpkgs = import ./dep/nixpkgs args;
+  nixpkgs = import ./nixpkgs.nix args;
   pkgs = nixpkgs.pkgsMusl;
 in 
   (import ./project.nix {