Simplify Nix expressions

This uses `developPackage` from `nixpkgs` to generate the derivation

Also add CI for nix build

.github/workflows/ci.yaml

@@ -56,3 +56,11 @@ jobs:
           path: dist-newstyle/sdist/brittany-*.tar.gz
           name: brittany-${{ github.sha }}.tar.gz
       - run: cabal check
+
+
+  nix:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: cachix/install-nix-action@v12
+      - uses: actions/checkout@v2
+      - run: nix-build

README.md

@@ -70,7 +70,7 @@ log the size of the input, but _not_ the full input/output of requests.)
 
 - via `nix`:
     ~~~.sh
-    nix build -f release.nix     # or 'nix-build -f release.nix'
+    nix build
     nix-env -i ./result
     ~~~
 
@@ -102,6 +102,20 @@ log the size of the input, but _not_ the full input/output of requests.)
     aura -A brittany
     ~~~~
 
+# Development tips
+
+## Run a hoogle server
+
+To host a local Hoogle server with all of Brittany's dependencies run:
+
+```sh
+echo brittany.cabal |
+  $(nix-build '<nixpkgs>' --no-link -A entr)/bin/entr -r -- \
+    sh -c "nix-shell --run 'hoogle server --local'"
+```
+
+This will watch `brittany.cabal` for changes and restart the server when new dependencies are added there.
+
 # Editor Integration
 
 #### Sublime text

default.nix

@@ -1,38 +1,18 @@
-{ mkDerivation, aeson, base, butcher, bytestring, cmdargs
-, containers, czipwith, data-tree-print, deepseq, directory, extra
-, filepath, ghc, ghc-boot-th, ghc-exactprint, ghc-paths, hspec
-, monad-memo, mtl, multistate, neat-interpolation, parsec, pretty
-, random, safe, semigroups, stdenv, strict, syb, text, transformers
-, uniplate, unsafe, yaml
+{ nixpkgsSrc ? builtins.fetchTarball {
+  url =
+    "https://github.com/nixos/nixpkgs/archive/069f183f16c3ea5d4b6e7625433b92eba77534f7.tar.gz"; # nixos-unstable
+  sha256 = "1by9rqvr2k6iz2yipf89yaj254yicpwq384ijgyy8p71lfxbbww2";
+}, pkgs ? import nixpkgsSrc { }, compiler ? null, forShell ? pkgs.lib.inNixShell
 }:
-mkDerivation {
-  pname = "brittany";
-  version = "0.11.0.0";
-  src = ./.;
-  isLibrary = true;
-  isExecutable = true;
-  libraryHaskellDepends = [
-    aeson base butcher bytestring cmdargs containers czipwith
-    data-tree-print deepseq directory extra filepath ghc ghc-boot-th
-    ghc-exactprint ghc-paths monad-memo mtl multistate
-    neat-interpolation pretty random safe semigroups strict syb text
-    transformers uniplate unsafe yaml
-  ];
-  executableHaskellDepends = [
-    aeson base butcher bytestring cmdargs containers czipwith
-    data-tree-print deepseq directory extra filepath ghc ghc-boot-th
-    ghc-exactprint ghc-paths monad-memo mtl multistate
-    neat-interpolation pretty safe semigroups strict syb text
-    transformers uniplate unsafe yaml
-  ];
-  testHaskellDepends = [
-    aeson base butcher bytestring cmdargs containers czipwith
-    data-tree-print deepseq directory extra filepath ghc ghc-boot-th
-    ghc-exactprint ghc-paths hspec monad-memo mtl multistate
-    neat-interpolation parsec pretty safe semigroups strict syb text
-    transformers uniplate unsafe yaml
-  ];
-  homepage = "https://github.com/lspitzner/brittany/";
-  description = "Haskell source code formatter";
-  license = stdenv.lib.licenses.agpl3;
+
+let
+  haskellPackages = if compiler == null then
+    pkgs.haskellPackages
+  else
+    pkgs.haskell.packages.${compiler};
+
+in haskellPackages.developPackage {
+  name = "brittany";
+  root = pkgs.nix-gitignore.gitignoreSource [ ] ./.;
+  returnShellEnv = forShell;
 }

pkgs.nix

@@ -1,5 +0,0 @@
-{
-  url = "https://github.com/nixos/nixpkgs.git";
-  ref = "release-18.09";
-  rev = "b9fa31cea0e119ecf1867af4944ddc2f7633aacd";
-}

release.nix

@@ -1,5 +0,0 @@
-{ pkgs ? import (fetchGit (import ./pkgs.nix)) {}
-, compiler ? "ghc822"
-}:
-
-pkgs.haskell.packages.${compiler}.callPackage ./shell.nix {}

shell.nix

@@ -1,13 +0,0 @@
-{ pkgs ? import (fetchGit (import ./pkgs.nix)) {}
-, compiler ? "ghc822"
-}:
-
-pkgs.haskell.packages.${compiler}.developPackage {
-  root = ./.;
-  name = "brittany";
-  overrides = with pkgs.haskell.lib; self: super: {
-  };
-  source-overrides = {
-    ghc-exactprint = "0.5.8.0";
-  };
-}