git: add config helper for hooks

modules/programs/git.nix

@@ -201,6 +201,21 @@ in {
         '';
       };
 
+      hooks = mkOption {
+        type = types.attrsOf types.path;
+        default = { };
+        example = literalExpression ''
+          {
+            pre-commit = ./pre-commit-script;
+          }
+        '';
+        description = ''
+          Configuration helper for Git hooks.
+          See <link xlink:href="https://git-scm.com/docs/githooks" />
+          for reference.
+        '';
+      };
+
       iniContent = mkOption {
         type = gitIniType;
         internal = true;
@@ -449,6 +464,15 @@ in {
       };
     })
 
+    (mkIf (cfg.hooks != { }) {
+      programs.git.iniContent = {
+        core.hooksPath = let
+          entries =
+            mapAttrsToList (name: path: { inherit name path; }) cfg.hooks;
+        in toString (pkgs.linkFarm "git-hooks" entries);
+      };
+    })
+
     (mkIf (cfg.aliases != { }) { programs.git.iniContent.alias = cfg.aliases; })
 
     (mkIf (lib.isAttrs cfg.extraConfig) {

tests/modules/programs/git/default.nix

@@ -5,4 +5,5 @@
   git-with-str-extra-config = ./git-with-str-extra-config.nix;
   git-with-signing-key-id = ./git-with-signing-key-id.nix;
   git-without-signing-key-id = ./git-without-signing-key-id.nix;
+  git-with-hooks = ./git-with-hooks.nix;
 }

tests/modules/programs/git/git-pre-commit-hook.sh

@@ -0,0 +1,2 @@
+#!/bin/sh
+echo "pre-commit hook..."

tests/modules/programs/git/git-with-hooks.nix

@@ -0,0 +1,26 @@
+{ pkgs, ... }:
+
+{
+  programs.git = {
+    enable = true;
+    hooks = { pre-commit = ./git-pre-commit-hook.sh; };
+  };
+
+  nmt.script = ''
+    function getGitConfig() {
+      ${pkgs.gitMinimal}/bin/git config \
+        --file $TESTED/home-files/.config/git/config \
+        --get $1
+    }
+
+    assertFileExists home-files/.config/git/config
+    hookPath=$(getGitConfig core.hooksPath)
+    assertLinkExists $hookPath/pre-commit
+
+    actual="$(readlink "$hookPath/pre-commit")"
+    expected="${./git-pre-commit-hook.sh}"
+    if [[ $actual != $expected ]]; then
+      fail "Symlink $hookPath/pre-commit should point to $expected via the Nix store, but it actually points to $actual."
+    fi
+  '';
+}