From dc3c678835ffe27293e98060f182a44ea8baebc2 Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Thu, 26 Sep 2019 00:19:37 +0200
Subject: [PATCH 1/7] Use the module system, delegate activation to project.nix
 core

New
 - Selectively enable tools (#2)
 - Make choice of tool versions overridable
 - User-definable hooks
 - Input validation at the Nix level

Fixes
 - Stop installing files all over the place when doing nix-shell ../some-project to borrow a tool
 - Lorri support

Cleanup
 - Get rid of installation code
---
 .pre-commit-config.yaml |  24 ++-
 modules/hooks.nix       |  83 +++++++++++
 modules/pre-commit.nix  | 319 ++++++++++++++++++++++++++++++++++++++++
 nix/packages.nix        |  12 +-
 nix/run.nix             | 142 +++++-------------
 nix/sources.json        |  24 +++
 6 files changed, 488 insertions(+), 116 deletions(-)
 create mode 100644 modules/hooks.nix
 create mode 100644 modules/pre-commit.nix

diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 21bba7ec..e1f54097 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -1,6 +1,18 @@
-repos:
-   - repo: .pre-commit-hooks/
-     rev: master
-     hooks:
-      -   id: shellcheck
-      -   id: canonix
+# DO NOT MODIFY
+# This file was generated by project.nix
+{
+  "repos": [
+    {
+      "hooks": [
+        {
+          "id": "canonix"
+        },
+        {
+          "id": "shellcheck"
+        }
+      ],
+      "repo": ".pre-commit-hooks/",
+      "rev": "master"
+    }
+  ]
+}
diff --git a/modules/hooks.nix b/modules/hooks.nix
new file mode 100644
index 00000000..f90786bb
--- /dev/null
+++ b/modules/hooks.nix
@@ -0,0 +1,83 @@
+{ config, lib, pkgs, ... }:
+let
+  inherit (config.pre-commit) tools;
+in {
+  config.pre-commit.hooks =
+    {
+      hlint =
+        {
+          name = "hlint";
+          description =
+            "HLint gives suggestions on how to improve your source code.";
+          entry = "${tools.hlint}/bin/hlint";
+          files = "\\.l?hs$";
+        };
+      ormolu =
+        {
+          name = "ormolu";
+          description = "Haskell code prettifier.";
+          entry = "${tools.ormolu}/bin/ormolu --mode inplace";
+          files = "\\.l?hs$";
+        };
+      hindent =
+        {
+          name = "hindent";
+          description = "Haskell code prettifier.";
+          entry = "${tools.hindent}/bin/hindent";
+          files = "\\.l?hs$";
+        };
+      cabal-fmt =
+        {
+          name = "cabal-fmt";
+          description = "Format Cabal files";
+          entry = "${tools.cabal-fmt}/bin/cabal-fmt --inplace";
+          files = "\\.cabal$";
+        };
+      canonix =
+        {
+          name = "canonix";
+          description = "Nix code prettifier.";
+          entry = "${tools.canonix}/bin/canonix";
+          files = "\\.nix$";
+        };
+      nixfmt =
+        {
+          name = "nixfmt";
+          description = "Nix code prettifier.";
+          entry = "${tools.nixfmt}/bin/nixfmt";
+          files = "\\.nix$";
+        };
+      nixpkgs-fmt =
+        {
+          name = "nixpkgs-fmt";
+          description = "Nix code prettifier.";
+          entry = "${tools.nixpkgs-fmt}/bin/nixpkgs-fmt -i";
+          files = "\\.nix$";
+        };
+      elm-format =
+        {
+          name = "elm-format";
+          description = "Format Elm files";
+          entry =
+            "${tools.elm-format}/bin/elm-format --yes --elm-version=0.19";
+          files = "\\.elm$";
+        };
+      shellcheck =
+        {
+          name = "shellcheck";
+          description = "Format shell files";
+          types =
+            [
+              "bash"
+            ];
+          entry = "${tools.shellcheck}/bin/shellcheck";
+        };
+      terraform-format =
+        {
+          name = "terraform-format";
+          description = "Format terraform (.tf) files";
+          entry = "${tools.terraform-fmt}/bin/terraform-fmt";
+          files = "\\.tf$";
+        };
+    };
+}
diff --git a/modules/pre-commit.nix b/modules/pre-commit.nix
new file mode 100644
index 00000000..b8df26c8
--- /dev/null
+++ b/modules/pre-commit.nix
@@ -0,0 +1,319 @@
+{ config, lib, pkgs, ... }:
+
+let
+
+  inherit (lib)
+    attrNames
+    concatStringsSep
+    filterAttrs
+    literalExample
+    mapAttrsToList
+    mkIf
+    mkOption
+    types
+    ;
+
+  inherit (pkgs) runCommand writeText git;
+
+  cfg = config.pre-commit;
+
+  hookType =
+    types.submodule (
+      { config, name, ... }:
+        {
+          options =
+            {
+              enable =
+                mkOption {
+                  type = types.bool;
+                  description = "Whether to enable this pre-commit hook.";
+                  default = false;
+                };
+              raw =
+                mkOption {
+                  type = types.attrsOf types.unspecified;
+                  description =
+                    ''
+                      Raw fields of a pre-commit hook. This is mostly for internal use but
+                      exposed in case you need to work around something.
+
+                      Default: taken from the other hook options.
+                    '';
+                };
+              name =
+                mkOption {
+                  type = types.str;
+                  default = name;
+                  defaultText = literalExample "internal name, same as id";
+                  description =
+                    ''
+                      The name of the hook - shown during hook execution.
+                    '';
+                };
+              entry =
+                mkOption {
+                  type = types.str;
+                  description =
+                    ''
+                      The entry point - the executable to run. entry can also contain arguments that will not be overridden such as entry: autopep8 -i.
+                    '';
+                };
+              language =
+                mkOption {
+                  type = types.str;
+                  description =
+                    ''
+                      The language of the hook - tells pre-commit how to install the hook.
+                    '';
+                  default = "system";
+                };
+              files =
+                mkOption {
+                  type = types.str;
+                  description =
+                    ''
+                      The pattern of files to run on.
+                    '';
+                  default = "";
+                };
+              types =
+                mkOption {
+                  type = types.listOf types.str;
+                  description =
+                    ''
+                      List of file types to run on. See Filtering files with types (https://pre-commit.com/#plugins).
+                    '';
+                  default = [ "file" ];
+                };
+              description =
+                mkOption {
+                  type = types.str;
+                  description =
+                    ''
+                      Description of the hook. used for metadata purposes only.
+                    '';
+                  default = "";
+                };
+              excludes =
+                mkOption {
+                  type = types.listOf types.str;
+                  description =
+                    ''
+                      Exclude files that were matched by these patterns.
+                    '';
+                  default = [];
+                };
+            };
+          config =
+            {
+              raw =
+                {
+                  inherit (config) name entry language files types;
+                  id = name;
+                  exclude =
+                    if config.excludes == [] then "^$" else
+                      "(${concatStringsSep "|" config.excludes})";
+                };
+            };
+        }
+    );
+
+  enabledHooks = filterAttrs ( id: value: value.enable ) cfg.hooks;
+  processedHooks =
+    mapAttrsToList ( id: value: value.raw // { inherit id; } ) enabledHooks;
+
+  precommitConfig =
+    {
+      repos =
+        [
+          {
+            repo = ".pre-commit-hooks/";
+            rev = "master";
+            hooks =
+              mapAttrsToList ( id: _value: { inherit id; } ) enabledHooks;
+          }
+        ];
+    };
+
+  hooksFile =
+    writeText "pre-commit-hooks.json" ( builtins.toJSON processedHooks );
+  configFile =
+    writeText "pre-commit-config.json" ( builtins.toJSON precommitConfig );
+
+  hooks =
+    runCommand "pre-commit-hooks-dir" { buildInputs = [ git ]; } ''
+      HOME=$PWD
+      mkdir -p $out
+      ln -s ${hooksFile} $out/.pre-commit-hooks.yaml
+      cd $out
+      git config --global user.email "you@example.com"
+      git config --global user.name "Your Name"
+      git init
+      git add .
+      git commit -m "init"
+    '';
+
+  run =
+    runCommand "pre-commit-run" { buildInputs = [ git ]; } ''
+      set +e
+      HOME=$PWD
+      cp --no-preserve=mode -R ${cfg.rootSrc} src
+      unlink src/.pre-commit-hooks || true
+      ln -fs ${hooks} src/.pre-commit-hooks
+      cd src
+      rm -rf src/.git
+      git init
+      git add .
+      git config --global user.email "you@example.com"
+      git config --global user.name "Your Name"
+      git commit -m "init"
+      echo "Running: $ pre-commit run --all-files"
+      ${cfg.package}/bin/pre-commit run --all-files
+      exitcode=$?
+      git --no-pager diff --color
+      touch $out
+      [ $? -eq 0 ] && exit $exitcode
+    '';
+
+  srcStr = toString ( config.root.origSrc or config.root );
+
+  # TODO: provide a default pin that the user may override
+  inherit (import (import ../nix/sources.nix).gitignore { inherit lib; })
+    gitignoreSource
+    ;
+in {
+  options.pre-commit =
+    {
+
+      enable =
+        mkOption {
+          type = types.bool;
+          default = false;
+          description =
+            ''
+              Whether to enable pre-commit integration.
+
+              https://pre-commit.com/
+            '';
+        };
+
+      enableAutoInstall =
+        mkOption {
+          type = types.bool;
+          default = true;
+          description =
+            ''
+              Whether to auto install pre-commit when invoking nix-shell in the
+              project root.
+            '';
+        };
+
+      package =
+        mkOption {
+          type = types.package;
+          description =
+            ''
+              The pre-commit package to use.
+            '';
+          default = pkgs.pre-commit;
+          defaultText =
+            literalExample ''
+        pkgs.pre-commit
+      '';
+        };
+
+      tools =
+        mkOption {
+          type = types.attrsOf types.package;
+          description =
+            ''
+              Tool set from which nix-pre-commit will pick binaries.
+
+              nix-pre-commit comes with its own set of packages for this purpose.
+            '';
+        };
+
+      hooks =
+        mkOption {
+          type = types.attrsOf hookType;
+          description =
+            ''
+              The hook definitions.
+            '';
+          default = {};
+        };
+
+      run =
+        mkOption {
+          type = types.package;
+          description =
+            ''
+              A derivation that tests whether the pre-commit hooks run cleanly on
+              the entire project.
+            '';
+          readOnly = true;
+          default = run;
+        };
+
+      rootSrc =
+        mkOption {
+          type = types.package;
+          description =
+            ''
+              The source of the project to be checked.
+            '';
+          defaultText = literalExample ''gitignoreSource config.root'';
+          default = gitignoreSource config.root;
+        };
+
+    };
+
+  config =
+    mkIf cfg.enable {
+
+      shell.packages = [ cfg.package ];
+
+      activation.hooks =
+        mkIf cfg.enableAutoInstall [
+          ''
+            export PATH=$PATH:${cfg.package}/bin
+            if ! type -t git >/dev/null; then
+              # This happens in pure shells, including lorri
+              echo 1>&2 "WARNING: nix-pre-commit-hooks: git command not found; skipping installation."
+            else
+              (
+                # We use srcStr to protect against installing pre-commit hooks
+                # in the wrong places such as for example ./. when invoking
+                #   nix-shell ../../other-project/shell.nix
+                cd ${lib.escapeShellArg srcStr} && {
+                  # Avoid filesystem churn. We may be watched!
+                  # This prevents lorri from looping after every interactive shell command.
+                  if readlink .pre-commit-hooks >/dev/null \
+                    && [[ $(readlink .pre-commit-hooks) == ${hooks} ]]; then
+                    echo 1>&2 "nix-pre-commit-hooks: hooks up to date"
+                  else
+                    echo 1>&2 "nix-pre-commit-hooks: updating" ${lib.escapeShellArg srcStr}
+
+                    [ -L .pre-commit-hooks ] && unlink .pre-commit-hooks
+                    ln -s ${hooks} .pre-commit-hooks
+
+                    # This can't be a symlink because its path is not constant,
+                    # thus can not be committed and is invisible to pre-commit.
+                    unlink .pre-commit-config.yaml
+                    { echo '# DO NOT MODIFY';
+                      echo '# This file was generated by project.nix';
+                      ${pkgs.jq}/bin/jq . <${configFile}
+                    } >.pre-commit-config.yaml
+
+                    pre-commit install
+                    # this is needed as the hook repo configuration is cached
+                    pre-commit clean
+                  fi
+                }
+              )
+            fi
+          ''
+        ];
+
+    };
+}
diff --git a/nix/packages.nix b/nix/packages.nix
index 45f18ee2..a939a55b 100644
--- a/nix/packages.nix
+++ b/nix/packages.nix
@@ -14,6 +14,14 @@ in
   tools // rec {
   inherit niv;
   inherit (gitAndTools) pre-commit;
-  run = import ./run.nix { inherit tools pre-commit runCommand writeText writeScript git; };
-  pre-commit-check = run { src = ../.; };
+  run = callPackage ./run.nix { inherit tools; };
+
+  # A pre-commit-check for nix-pre-commit itself
+  pre-commit-check = run {
+    src = ../.;
+    hooks = {
+      shellcheck.enable = true;
+      canonix.enable = true;
+    };
+  };
 }
diff --git a/nix/run.nix b/nix/run.nix
index 3bbe2df2..7e32f048 100644
--- a/nix/run.nix
+++ b/nix/run.nix
@@ -1,116 +1,42 @@
-{ tools, pre-commit, git, runCommand, writeText, writeScript }:
+{ pkgs, tools, pre-commit, git, runCommand, writeText, writeScript, lib }:
 
 { src
-, hooks ? null
+, hooks ? {}
 }:
 
 let
-  hooksYaml =
-    writeText "pre-commit-hooks" ''
-  -   id: hlint
-      name: hlint
-      description: HLint gives suggestions on how to improve your source code.
-      entry: ${tools.hlint}/bin/hlint
-      language: system
-      files: '\.l?hs$'
-  -   id: ormolu
-      name: ormolu
-      description: Haskell code prettifier.
-      entry: ${tools.ormolu}/bin/ormolu --mode inplace
-      language: script
-      files: '\.l?hs$'
-  -   id: hindent
-      name: hindent
-      description: Haskell code prettifier.
-      entry: ${tools.hindent}/bin/hindent
-      language: script
-      files: '\.l?hs$'
-  -   id: cabal-fmt
-      name: cabal-fmt
-      description: Format Cabal files
-      entry: ${tools.cabal-fmt}/bin/cabal-fmt --inplace 
-      language: script
-      files: '\.cabal$'
-  -   id: canonix
-      name: canonix
-      description: Nix code prettifier.
-      entry: ${tools.canonix}/bin/canonix
-      language: system
-      files: '\.nix$'
-  -   id: nixfmt
-      name: nixfmt
-      description: Nix code prettifier.
-      entry: ${tools.nixfmt}/bin/nixfmt
-      language: script
-      files: '\.nix$'
-  -   id: nixpkgs-fmt
-      name: nixpkgs-fmt
-      description: Nix code prettifier.
-      entry: ${tools.nixpkgs-fmt}/bin/nixpkgs-fmt -i
-      language: script
-      files: '\.nix$'
-  -   id: elm-format
-      name: elm-format
-      description: Format Elm files
-      entry: ${tools.elm-format}/bin/elm-format --yes --elm-version=0.19
-      language: script
-      files: \.elm$
-  -   id: shellcheck
-      name: shellcheck
-      description: Format shell files
-      types: [bash]
-      entry: ${tools.shellcheck}/bin/shellcheck
-      language: system
-  -   id: terraform-format
-      name: terraform-format
-      description: Format terraform (.tf) files
-      entry: ${tools.terraform-fmt}/bin/terraform-fmt
-      files: '\.tf$'
-      language: script
-  '';
+  sources = import ./sources.nix;
 
-  hooks =
-    runCommand "pre-commit-hooks-dir" { buildInputs = [ git ]; } ''
-    HOME=$PWD
-    mkdir -p $out
-    ln -s ${hooksYaml} $out/.pre-commit-hooks.yaml
-    cd $out
-    git config --global user.email "you@example.com"
-    git config --global user.name "Your Name"
-    git init
-    git add .
-    git commit -m "init"
-  '';
+  # TODO upstream this and add tests to support this use case
+  project-nix-core =
+    map ( f: sources."project.nix" + ("/" + f) ) [
+      "modules/root.nix"
+      "modules/activation.nix"
+      "modules/shell.nix"
+      "modules/nixpkgs.nix"
+    ];
+
+  project =
+    lib.evalModules {
+      modules =
+        project-nix-core ++ [
+          {
+            root = src;
+            nixpkgs.pkgs = pkgs;
+            pre-commit.tools = lib.mkDefault tools;
+            pre-commit.enable = true;
+            pre-commit.hooks = hooks;
+          }
+          ../modules/pre-commit.nix
+          ../modules/hooks.nix
+      ];
+    };
+  inherit (project.config.shell.shell) shellHook activationHook;
 
-  run =
-    runCommand "pre-commit-run" { buildInputs = [ git ]; } ''
-    set +e
-    HOME=$PWD
-    cp --no-preserve=mode -R ${src} src
-    unlink src/.pre-commit-hooks || true
-    ln -fs ${hooks} src/.pre-commit-hooks
-    cd src
-    rm -rf src/.git
-    git init
-    git add .
-    git config --global user.email "you@example.com"
-    git config --global user.name "Your Name"
-    git commit -m "init"
-    echo "Running: $ pre-commit run --all-files"
-    ${pre-commit}/bin/pre-commit run --all-files
-    exitcode=$?
-    git diff
-    touch $out
-    [ $? -eq 0 ] && exit $exitcode
-  '';
 in
-  run // {
-  shellHook = ''
-    [ -L .pre-commit-hooks ] && unlink .pre-commit-hooks
-    ln -s ${hooks} .pre-commit-hooks
-    export PATH=$PATH:${pre-commit}/bin
-    pre-commit install
-    # this is needed as the hook repo configuration is cached
-    pre-commit clean
-  '';
-}
+  project.config.pre-commit.run // {
+    shellHook = ''
+      activationHook=${lib.escapeShellArg activationHook}
+      ${shellHook}
+    '';
+  }
diff --git a/nix/sources.json b/nix/sources.json
index 2c99ae69..fd7c401c 100644
--- a/nix/sources.json
+++ b/nix/sources.json
@@ -23,6 +23,18 @@
         "url": "https://github.com/hercules-ci/canonix/archive/a3369542aef56366d3432e01e3e73374a310ca4a.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
+    "gitignore": {
+        "branch": "master",
+        "description": "Nix function for filtering local git sources",
+        "homepage": "",
+        "owner": "hercules-ci",
+        "repo": "gitignore",
+        "rev": "f9e996052b5af4032fe6150bba4a6fe4f7b9d698",
+        "sha256": "0jrh5ghisaqdd0vldbywags20m2cxpkbbk5jjjmwaw0gr8nhsafv",
+        "type": "tarball",
+        "url": "https://github.com/hercules-ci/gitignore/archive/f9e996052b5af4032fe6150bba4a6fe4f7b9d698.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
     "haskell.nix": {
         "branch": "master",
         "description": "Alternative Haskell Infrastructure for Nixpkgs",
@@ -106,5 +118,17 @@
         "type": "tarball",
         "url": "https://github.com/tweag/ormolu/archive/a7076c0f83e5c06ea9067b71171859fa2ba8afd9.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
+    "project.nix": {
+        "branch": "pre-commit",
+        "description": "A configuration manager for your projects",
+        "homepage": null,
+        "owner": "hercules-ci",
+        "repo": "project.nix",
+        "rev": "ec17ac79904a296f358961ffcff7a13948c2b92e",
+        "sha256": "1gkb9k995ly53d5sxn5hr4lyzh57sq25j3i2cw8zva92g8x69gb5",
+        "type": "tarball",
+        "url": "https://github.com/hercules-ci/project.nix/archive/ec17ac79904a296f358961ffcff7a13948c2b92e.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     }
 }

From 2739673f91fdc507d2f111ca8bed4b1ab51a60b6 Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Thu, 26 Sep 2019 00:56:20 +0200
Subject: [PATCH 2/7] Update README.md for module system change

---
 README.md | 25 +++++++++----------------
 1 file changed, 9 insertions(+), 16 deletions(-)

diff --git a/README.md b/README.md
index 32e8c003..f3d4a122 100644
--- a/README.md
+++ b/README.md
@@ -17,39 +17,32 @@ The goal is to manage these hooks with Nix and solve the following:
 
 # Installation & Usage
 
-1. Create `.pre-commit-config.yaml` with hooks you want to run in your git repository:
-   ```yaml
-   repos:
-   - repo: .pre-commit-hooks/
-     rev: master
-     hooks:
-      -   id: ormolu
-      -   id: shellcheck
-      -   id: elm-format
-   ```
-
-2. (optional) Use binary caches to avoid compilation:
+1. (optional) Use binary caches to avoid compilation:
 
    ```bash
    $ nix-env -iA cachix -f https://cachix.org/api/v1/install
    $ cachix use hercules-ci
    ```
 
-3. Integrate hooks to be built as part of `default.nix`:
+2. Integrate hooks to be built as part of `default.nix`:
    ```nix
     let
-      inherit (import (builtins.fetchTarball "https://github.com/hercules-ci/gitignore/tarball/master" {})) gitignoreSource;
       nix-pre-commit-hooks = import (builtins.fetchTarball "https://github.com/hercules-ci/nix-pre-commit-hooks/tarball/master");
     in {
       pre-commit-check = nix-pre-commit-hooks.run {
-        src = gitignoreSource ./.;
+        src = ./.;
+        hooks = {
+          elm-format.enable = true;
+          ormolu.enable = true;
+          shellcheck.enable = true;
+        };
       };
     }
    ```
 
    Run `$ nix-build -A pre-commit-check` to perform the checks as a Nix derivation.
 
-2. Integrate hooks to prepare environment as part of `shell.nix`:
+3. Integrate hooks to prepare environment as part of `shell.nix`:
    ```nix
     (import <nixpkgs> {}).mkShell {
       inherit ((import ./. {}).pre-commit-check) shellHook;

From 669b2f3da6283a09d88b8b9c41b64f5fe8001d78 Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Tue, 1 Oct 2019 23:21:03 +0200
Subject: [PATCH 3/7] Invert project.nix dependency, simplify installation
 script

---
 .pre-commit-config.yaml |  2 +-
 modules/pre-commit.nix  | 80 ++++++++++++++++++++---------------------
 nix/project-module.nix  | 11 ++++++
 nix/run.nix             | 45 ++++++++++++-----------
 nix/sources.json        | 12 -------
 5 files changed, 72 insertions(+), 78 deletions(-)
 create mode 100644 nix/project-module.nix

diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index e1f54097..93eb75a6 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -1,5 +1,5 @@
 # DO NOT MODIFY
-# This file was generated by project.nix
+# This file was generated by nix-pre-commit-hooks
 {
   "repos": [
     {
diff --git a/modules/pre-commit.nix b/modules/pre-commit.nix
index b8df26c8..8a72caaa 100644
--- a/modules/pre-commit.nix
+++ b/modules/pre-commit.nix
@@ -175,8 +175,6 @@ let
       [ $? -eq 0 ] && exit $exitcode
     '';
 
-  srcStr = toString ( config.root.origSrc or config.root );
-
   # TODO: provide a default pin that the user may override
   inherit (import (import ../nix/sources.nix).gitignore { inherit lib; })
     gitignoreSource
@@ -255,6 +253,16 @@ in {
           default = run;
         };
 
+      installationScript =
+        mkOption {
+          type = types.str;
+          description =
+            ''
+              A bash snippet that installs nix-pre-commit in the current directory
+            '';
+          readOnly = true;
+        };
+
       rootSrc =
         mkOption {
           type = types.package;
@@ -269,51 +277,39 @@ in {
     };
 
   config =
-    mkIf cfg.enable {
-
-      shell.packages = [ cfg.package ];
+    {
 
-      activation.hooks =
-        mkIf cfg.enableAutoInstall [
-          ''
-            export PATH=$PATH:${cfg.package}/bin
-            if ! type -t git >/dev/null; then
-              # This happens in pure shells, including lorri
-              echo 1>&2 "WARNING: nix-pre-commit-hooks: git command not found; skipping installation."
+      pre-commit.installationScript =
+        ''
+          export PATH=$PATH:${cfg.package}/bin
+          if ! type -t git >/dev/null; then
+            # This happens in pure shells, including lorri
+            echo 1>&2 "WARNING: nix-pre-commit-hooks: git command not found; skipping installation."
+          else
+            # Avoid filesystem churn. We may be watched!
+            # This prevents lorri from looping after every interactive shell command.
+            if readlink .pre-commit-hooks >/dev/null \
+              && [[ $(readlink .pre-commit-hooks) == ${hooks} ]]; then
+              echo 1>&2 "nix-pre-commit-hooks: hooks up to date"
             else
-              (
-                # We use srcStr to protect against installing pre-commit hooks
-                # in the wrong places such as for example ./. when invoking
-                #   nix-shell ../../other-project/shell.nix
-                cd ${lib.escapeShellArg srcStr} && {
-                  # Avoid filesystem churn. We may be watched!
-                  # This prevents lorri from looping after every interactive shell command.
-                  if readlink .pre-commit-hooks >/dev/null \
-                    && [[ $(readlink .pre-commit-hooks) == ${hooks} ]]; then
-                    echo 1>&2 "nix-pre-commit-hooks: hooks up to date"
-                  else
-                    echo 1>&2 "nix-pre-commit-hooks: updating" ${lib.escapeShellArg srcStr}
+              echo 1>&2 "nix-pre-commit-hooks: updating $PWD"
 
-                    [ -L .pre-commit-hooks ] && unlink .pre-commit-hooks
-                    ln -s ${hooks} .pre-commit-hooks
+              [ -L .pre-commit-hooks ] && unlink .pre-commit-hooks
+              ln -s ${hooks} .pre-commit-hooks
 
-                    # This can't be a symlink because its path is not constant,
-                    # thus can not be committed and is invisible to pre-commit.
-                    unlink .pre-commit-config.yaml
-                    { echo '# DO NOT MODIFY';
-                      echo '# This file was generated by project.nix';
-                      ${pkgs.jq}/bin/jq . <${configFile}
-                    } >.pre-commit-config.yaml
+              # This can't be a symlink because its path is not constant,
+              # thus can not be committed and is invisible to pre-commit.
+              unlink .pre-commit-config.yaml
+              { echo '# DO NOT MODIFY';
+                echo '# This file was generated by nix-pre-commit-hooks';
+                ${pkgs.jq}/bin/jq . <${configFile}
+              } >.pre-commit-config.yaml
 
-                    pre-commit install
-                    # this is needed as the hook repo configuration is cached
-                    pre-commit clean
-                  fi
-                }
-              )
+              pre-commit install
+              # this is needed as the hook repo configuration is cached
+              pre-commit clean
             fi
-          ''
-        ];
-
+          fi
+        '';
     };
 }
diff --git a/nix/project-module.nix b/nix/project-module.nix
new file mode 100644
index 00000000..4055367a
--- /dev/null
+++ b/nix/project-module.nix
@@ -0,0 +1,11 @@
+/*
+  This module is picked up by project.nix but is also used internally
+  to find these imported modules.
+ */
+{
+  imports =
+    [
+      ../modules/pre-commit.nix
+      ../modules/hooks.nix
+    ];
+}
diff --git a/nix/run.nix b/nix/run.nix
index 7e32f048..3bc29860 100644
--- a/nix/run.nix
+++ b/nix/run.nix
@@ -7,36 +7,35 @@
 let
   sources = import ./sources.nix;
 
-  # TODO upstream this and add tests to support this use case
-  project-nix-core =
-    map ( f: sources."project.nix" + ("/" + f) ) [
-      "modules/root.nix"
-      "modules/activation.nix"
-      "modules/shell.nix"
-      "modules/nixpkgs.nix"
-    ];
-
   project =
     lib.evalModules {
       modules =
-        project-nix-core ++ [
+        [
+          ./project-module.nix
           {
-            root = src;
-            nixpkgs.pkgs = pkgs;
-            pre-commit.tools = lib.mkDefault tools;
-            pre-commit.enable = true;
-            pre-commit.hooks = hooks;
+            options =
+              {
+                root =
+                  lib.mkOption {
+                    description = "Internal option";
+                    default = src;
+                    internal = true;
+                    readOnly = true;
+                    type = lib.types.unspecified;
+                  };
+              };
+            config =
+              {
+                _module.args.pkgs = pkgs;
+                pre-commit.hooks = hooks;
+                pre-commit.tools = lib.mkDefault tools;
+              };
           }
-          ../modules/pre-commit.nix
-          ../modules/hooks.nix
-      ];
+        ];
     };
-  inherit (project.config.shell.shell) shellHook activationHook;
+  inherit (project.config.pre-commit) installationScript;
 
 in
   project.config.pre-commit.run // {
-    shellHook = ''
-      activationHook=${lib.escapeShellArg activationHook}
-      ${shellHook}
-    '';
+    shellHook = installationScript;
   }
diff --git a/nix/sources.json b/nix/sources.json
index fd7c401c..e7b8c79a 100644
--- a/nix/sources.json
+++ b/nix/sources.json
@@ -118,17 +118,5 @@
         "type": "tarball",
         "url": "https://github.com/tweag/ormolu/archive/a7076c0f83e5c06ea9067b71171859fa2ba8afd9.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
-    },
-    "project.nix": {
-        "branch": "pre-commit",
-        "description": "A configuration manager for your projects",
-        "homepage": null,
-        "owner": "hercules-ci",
-        "repo": "project.nix",
-        "rev": "ec17ac79904a296f358961ffcff7a13948c2b92e",
-        "sha256": "1gkb9k995ly53d5sxn5hr4lyzh57sq25j3i2cw8zva92g8x69gb5",
-        "type": "tarball",
-        "url": "https://github.com/hercules-ci/project.nix/archive/ec17ac79904a296f358961ffcff7a13948c2b92e.tar.gz",
-        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     }
 }

From 7a3985167c26a4188d8921ae2212be56e21b359b Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Wed, 2 Oct 2019 00:17:31 +0200
Subject: [PATCH 4/7] Remove redundant enable options

---
 modules/pre-commit.nix | 23 -----------------------
 1 file changed, 23 deletions(-)

diff --git a/modules/pre-commit.nix b/modules/pre-commit.nix
index 8a72caaa..2b2c1216 100644
--- a/modules/pre-commit.nix
+++ b/modules/pre-commit.nix
@@ -183,29 +183,6 @@ in {
   options.pre-commit =
     {
 
-      enable =
-        mkOption {
-          type = types.bool;
-          default = false;
-          description =
-            ''
-              Whether to enable pre-commit integration.
-
-              https://pre-commit.com/
-            '';
-        };
-
-      enableAutoInstall =
-        mkOption {
-          type = types.bool;
-          default = true;
-          description =
-            ''
-              Whether to auto install pre-commit when invoking nix-shell in the
-              project root.
-            '';
-        };
-
       package =
         mkOption {
           type = types.package;

From b9957b52b488fc23fbc0479b6567cbef214a11cb Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Wed, 2 Oct 2019 01:02:52 +0200
Subject: [PATCH 5/7] Extract nix/tools.nix

---
 modules/pre-commit.nix |  5 +++++
 nix/packages.nix       | 12 ++----------
 nix/tools.nix          | 10 ++++++++++
 3 files changed, 17 insertions(+), 10 deletions(-)
 create mode 100644 nix/tools.nix

diff --git a/modules/pre-commit.nix b/modules/pre-commit.nix
index 2b2c1216..846aabd1 100644
--- a/modules/pre-commit.nix
+++ b/modules/pre-commit.nix
@@ -206,6 +206,11 @@ in {
 
               nix-pre-commit comes with its own set of packages for this purpose.
             '';
+          # This default is for when the module is the entry point rather than
+          # /default.nix. /default.nix will override this for efficiency.
+          default = (import ../nix {}).callPackage ../nix/tools.nix {};
+          defaultText =
+            literalExample ''nix-pre-commit-hooks-pkgs.callPackage tools-dot-nix {}'';
         };
 
       hooks =
diff --git a/nix/packages.nix b/nix/packages.nix
index a939a55b..b7a7af2f 100644
--- a/nix/packages.nix
+++ b/nix/packages.nix
@@ -1,15 +1,7 @@
-{ hlint, shellcheck, ormolu, hindent, cabal-fmt, canonix, elmPackages, niv
-, gitAndTools, runCommand, writeText, writeScript, git, nixpkgs-fmt, nixfmt
-, callPackage
-}:
+{ niv, gitAndTools, callPackage }:
 
 let
-  tools =
-    {
-      inherit hlint shellcheck ormolu hindent cabal-fmt canonix nixpkgs-fmt nixfmt;
-      inherit (elmPackages) elm-format;
-      terraform-fmt = callPackage ./terraform-fmt {};
-    };
+  tools = callPackage ./tools.nix {};
 in
   tools // rec {
   inherit niv;
diff --git a/nix/tools.nix b/nix/tools.nix
new file mode 100644
index 00000000..fd16db96
--- /dev/null
+++ b/nix/tools.nix
@@ -0,0 +1,10 @@
+{ hlint, shellcheck, ormolu, hindent, cabal-fmt, canonix, elmPackages, niv
+, gitAndTools, runCommand, writeText, writeScript, git, nixpkgs-fmt, nixfmt
+, callPackage
+}:
+
+{
+  inherit hlint shellcheck ormolu hindent cabal-fmt canonix nixpkgs-fmt nixfmt;
+  inherit (elmPackages) elm-format;
+  terraform-fmt = callPackage ./terraform-fmt {};
+}

From 03e3814200fca27ad7ef241f76a8e90d54874baf Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Wed, 2 Oct 2019 01:06:59 +0200
Subject: [PATCH 6/7] Set up project-module.nix as a proper entrypoint

---
 modules/all-modules.nix | 7 +++++++
 nix/project-module.nix  | 5 +++--
 nix/run.nix             | 2 +-
 3 files changed, 11 insertions(+), 3 deletions(-)
 create mode 100644 modules/all-modules.nix

diff --git a/modules/all-modules.nix b/modules/all-modules.nix
new file mode 100644
index 00000000..9a72a78c
--- /dev/null
+++ b/modules/all-modules.nix
@@ -0,0 +1,7 @@
+{
+  imports =
+    [
+      ./pre-commit.nix
+      ./hooks.nix
+    ];
+}
diff --git a/nix/project-module.nix b/nix/project-module.nix
index 4055367a..ec43244f 100644
--- a/nix/project-module.nix
+++ b/nix/project-module.nix
@@ -5,7 +5,8 @@
 {
   imports =
     [
-      ../modules/pre-commit.nix
-      ../modules/hooks.nix
+      ../modules/all-modules.nix
     ];
+
+  # TODO: move project.nix/modules/pre-commit.nix here
 }
diff --git a/nix/run.nix b/nix/run.nix
index 3bc29860..fb328e50 100644
--- a/nix/run.nix
+++ b/nix/run.nix
@@ -11,7 +11,7 @@ let
     lib.evalModules {
       modules =
         [
-          ./project-module.nix
+          ../modules/all-modules.nix
           {
             options =
               {

From bd07c08450731fa42206d42709e3244526b05f3a Mon Sep 17 00:00:00 2001
From: Robert Hensing <robert@roberthensing.nl>
Date: Wed, 2 Oct 2019 10:16:33 +0200
Subject: [PATCH 7/7] Add changelog, update readme

---
 CHANGELOG.md | 34 ++++++++++++++++++++++++++++++++++
 README.md    |  3 +++
 2 files changed, 37 insertions(+)
 create mode 100644 CHANGELOG.md

diff --git a/CHANGELOG.md b/CHANGELOG.md
new file mode 100644
index 00000000..67d291ed
--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,34 @@
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is loosely based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
+and is a rolling release.
+
+## 2019-10-02
+
+### Added
+
+- The `run` derivation now uses [gitignore](https://github.com/hercules-ci/gitignore#readme)
+
+- Custom hooks can now be added
+
+### Changed
+
+- Hooks configuration is now module-based (using the module system, like NixOS).
+  `.pre-commit-config.yaml` is now obsolete with `nix-pre-commit-hooks`. Translate it to the `hooks` argument. For example:
+
+  ```
+  pre-commit-check = nix-pre-commit-hooks.run {
+    src = ./.;
+    hooks = {
+      elm-format.enable = true;
+      ormolu.enable = true;
+      shellcheck.enable = true;
+    };
+  };
+  ```
+
+### Fixed
+
+- Some small improvements to the installation script (`shellHook`)
diff --git a/README.md b/README.md
index f3d4a122..321ecb82 100644
--- a/README.md
+++ b/README.md
@@ -102,6 +102,9 @@ eval "$shellHook"
 
 Everyone is encouraged to add new hooks.
 
+<!-- TODO generate option docs -->
+Have a look at the [existing hooks](modules/hooks.nix) and the [options](modules/pre-commit.nix).
+
 There's no guarantee the hook will be accepted, but the general guidelines are:
 
 - Nix closure of the tool should be small e.g. `< 50MB`