Merge pull request #489 from cachix/add-gc-root

feat: create a GC root for the generated `.pre-commit-config.yaml`

Author: domenkozar

modules/pre-commit.nix

@@ -2,6 +2,7 @@
 let
   inherit (lib)
     attrNames
+    boolToString
     concatStringsSep
     compare
     filterAttrs
@@ -281,6 +282,15 @@ in
           internal = true;
         };
 
+      addGcRoot = mkOption {
+        type = types.bool;
+        default = true;
+        description = ''
+          Whether to add the generated pre-commit-config.yaml to the garbage collector roots.
+          This prevents Nix from garbage-collecting the tools used by hooks.
+        '';
+      };
+
       assertions = lib.mkOption {
         type = types.listOf types.unspecified;
         internal = true;
@@ -351,7 +361,11 @@ in
                 echo 1>&2 "    2. remove .pre-commit-config.yaml"
                 echo 1>&2 "    3. add .pre-commit-config.yaml to .gitignore"
               else
-                ln -fs ${configFile} "''${GIT_WC}/.pre-commit-config.yaml"
+                if ${boolToString cfg.addGcRoot}; then
+                  nix-store --add-root "''${GIT_WC}/.pre-commit-config.yaml" --indirect --realise ${configFile}
+                else
+                  ln -fs ${configFile} "''${GIT_WC}/.pre-commit-config.yaml"
+                fi
                 # Remove any previously installed hooks (since pre-commit itself has no convergent design)
                 hooks="${concatStringsSep " " (remove "manual" supportedHooksLib.supportedHooks )}"
                 for hook in $hooks; do

nix/installation-test.nix

@@ -61,7 +61,7 @@ let
 
   executeTest = lib.mapAttrsToList
     (name: test:
-      let runDerivation = run ({ src = null; } // test.conf);
+      let runDerivation = run ({ src = null; addGcRoot = false; } // test.conf);
       in ''
         rm -f ~/.git/hooks/*
         ${runDerivation.shellHook}

nix/run.nix

@@ -6,6 +6,7 @@ builtinStuff@{ pkgs, tools, isFlakes, pre-commit, git, runCommand, writeText, wr
 , excludes ? [ ]
 , tools ? { }
 , default_stages ? [ "commit" ]
+, addGcRoot ? true
 , imports ? [ ]
 }:
 let
@@ -19,7 +20,7 @@ let
               {
                 _module.args.pkgs = pkgs;
                 _module.args.gitignore-nix-src = gitignore-nix-src;
-                inherit hooks excludes default_stages settings;
+                inherit hooks excludes default_stages settings addGcRoot;
                 tools = builtinStuff.tools // tools;
                 package = pre-commit;
               } // (if isFlakes