Flakes support

.github/workflows/ci.yaml

@@ -16,3 +16,22 @@ jobs:
         name: pre-commit-hooks
         signingKey: '${{ secrets.CACHIX_SIGNING_KEY }}'
     - run: nix-build
+  tests-flakes:
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+    runs-on: ${{ matrix.os }}
+    steps:
+    - uses: actions/checkout@v2
+    - uses: cachix/install-nix-action@v13
+      with:
+          install_url: https://nixos-nix-install-tests.cachix.org/serve/lb41az54kzk6j12p81br4bczary7m145/install
+          install_options: '--tarball-url-prefix https://nixos-nix-install-tests.cachix.org/serve'
+          extra_nix_config: |
+            experimental-features = nix-command flakes
+    - uses: cachix/cachix-action@v10
+      with:
+        name: pre-commit-hooks
+        signingKey: '${{ secrets.CACHIX_SIGNING_KEY }}'
+    - run: nix flake check
+    - run: nix eval .#lib.x86_64-linux.run

flake.nix

@@ -0,0 +1,21 @@
+{
+  description = "Seamless integration of https://pre-commit.com git hooks with Nix.";
+
+  inputs.flake-utils.url = "github:numtide/flake-utils";
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        exposed = import ./nix { nixpkgs = nixpkgs; inherit system; gitignore-nix-src = null; isFlakes = true; };
+      in
+      {
+        packages = exposed.packages;
+
+        defaultPackage = exposed.packages.pre-commit;
+
+        checks = exposed.checks;
+
+        lib = { inherit (exposed) run; };
+      }
+    );
+}

modules/pre-commit.nix

@@ -163,11 +163,6 @@ let
       touch $out
       [ $? -eq 0 ] && exit $exitcode
     '';
-
-  # TODO: provide a default pin that the user may override
-  inherit (import (import ../nix/sources.nix)."gitignore.nix" { inherit lib; })
-    gitignoreSource
-    ;
 in
 {
   options =
@@ -180,7 +175,6 @@ in
             ''
               The pre-commit package to use.
             '';
-          default = pkgs.pre-commit;
           defaultText =
             literalExample ''
               pkgs.pre-commit
@@ -190,16 +184,12 @@ in
       tools =
         mkOption {
           type = types.lazyAttrsOf 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.
             '';
-          # 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 { inherit (pkgs) system; }).callPackage ../nix/tools.nix { };
           defaultText =
             literalExample ''nix-pre-commit-hooks-pkgs.callPackage tools-dot-nix { inherit (pkgs) system; }'';
         };
@@ -247,15 +237,14 @@ in
 
       rootSrc =
         mkOption {
-          type = types.package;
+          type = types.path;
           description =
             ''
               The source of the project to be checked.
 
               This is used in the derivation that performs the check.
             '';
           defaultText = literalExample ''gitignoreSource config.src'';
-          default = gitignoreSource config.src;
         };
 
       excludes =

nix/default.nix

@@ -1,25 +1,26 @@
 { sources ? import ./sources.nix
 , system ? builtins.currentSystem
 , nixpkgs ? sources.nixpkgs
+, gitignore-nix-src ? sources."gitignore.nix"
+, isFlakes ? false
 }:
 let
   overlay =
-    _: pkgs:
+    self: pkgs:
     let
-      run = pkgs.callPackage ./run.nix { inherit tools; };
-      tools = pkgs.callPackage ./tools.nix { };
+      tools = pkgs.lib.filterAttrs (k: v: !(pkgs.lib.any (a: k == a) [ "override" "overrideDerivation" ])) (pkgs.callPackage ./tools.nix { });
+      run = pkgs.callPackage ./run.nix { inherit pkgs tools isFlakes gitignore-nix-src; };
     in
     {
       inherit (pkgs) nixfmt niv ormolu nixpkgs-fmt nix-linter;
       cabal-fmt = pkgs.haskell.lib.enableSeparateBinOutput pkgs.haskellPackages.cabal-fmt;
       hindent = pkgs.haskell.lib.enableSeparateBinOutput pkgs.haskellPackages.hindent;
-      inherit tools;
+      inherit tools run;
       # Flake style attributes
-      packages = {
-        inherit tools run;
-        inherit (pkgs.gitAndTools) pre-commit;
+      packages = tools // {
+        inherit (pkgs) pre-commit;
       };
-      checks = tools // {
+      checks = self.packages // {
         # A pre-commit-check for nix-pre-commit itself
         pre-commit-check = run {
           src = ../.;

nix/run.nix

@@ -1,4 +1,4 @@
-builtinStuff@{ pkgs, tools, pre-commit, git, runCommand, writeText, writeScript, lib }:
+builtinStuff@{ pkgs, tools, isFlakes, pre-commit, git, runCommand, writeText, writeScript, lib, gitignore-nix-src }:
 
 { src
 , hooks ? { }
@@ -8,8 +8,6 @@ builtinStuff@{ pkgs, tools, pre-commit, git, runCommand, writeText, writeScript,
 , default_stages ? [ ]
 }:
 let
-  sources = import ./sources.nix;
-
   project =
     lib.evalModules {
       modules =
@@ -19,9 +17,15 @@ let
             config =
               {
                 _module.args.pkgs = pkgs;
-                inherit hooks excludes settings src default_stages;
+                _module.args.gitignore-nix-src = gitignore-nix-src;
+                inherit hooks excludes settings default_stages;
                 tools = builtinStuff.tools // tools;
-              };
+                package = pre-commit;
+              } // (if isFlakes
+              then { rootSrc = src; }
+              else {
+                rootSrc = (import gitignore-nix-src { inherit (pkgs) lib; }).gitignoreSource src;
+              });
           }
         ];
     };