pre-commit: stop using the flake

The flake for pre-commit-checks is rather questionable. We ignored
it so it uses our own nixpkgs and doesn't reimport nixpkgs. This should
save a couple of seconds of eval time!

Change-Id: I4584982beb32e0122f791fa29f6a544bdbb9e201

flake.lock

@@ -16,45 +16,6 @@
         "type": "github"
       }
     },
-    "flake-utils": {
-      "inputs": {
-        "systems": "systems"
-      },
-      "locked": {
-        "lastModified": 1710146030,
-        "narHash": "sha256-SZ5L6eA7HJ/nmkzGG7/ISclqe6oZdOZTNoesiInkXPQ=",
-        "owner": "numtide",
-        "repo": "flake-utils",
-        "rev": "b1d9ab70662946ef0850d488da1c9019f3a9752a",
-        "type": "github"
-      },
-      "original": {
-        "owner": "numtide",
-        "repo": "flake-utils",
-        "type": "github"
-      }
-    },
-    "gitignore": {
-      "inputs": {
-        "nixpkgs": [
-          "pre-commit-hooks",
-          "nixpkgs"
-        ]
-      },
-      "locked": {
-        "lastModified": 1709087332,
-        "narHash": "sha256-HG2cCnktfHsKV0s4XW83gU3F57gaTljL9KNSuG6bnQs=",
-        "owner": "hercules-ci",
-        "repo": "gitignore.nix",
-        "rev": "637db329424fd7e46cf4185293b9cc8c88c95394",
-        "type": "github"
-      },
-      "original": {
-        "owner": "hercules-ci",
-        "repo": "gitignore.nix",
-        "type": "github"
-      }
-    },
     "nixpkgs": {
       "locked": {
         "lastModified": 1711481231,
@@ -88,25 +49,13 @@
       }
     },
     "pre-commit-hooks": {
-      "inputs": {
+      "flake": false,
-        "flake-compat": [
-          "flake-compat"
-        ],
-        "flake-utils": "flake-utils",
-        "gitignore": "gitignore",
-        "nixpkgs": [
-          "nixpkgs"
-        ],
-        "nixpkgs-stable": [
-          "nixpkgs"
-        ]
-      },
       "locked": {
-        "lastModified": 1711981679,
+        "lastModified": 1712055707,
-        "narHash": "sha256-pnbHEXJOdGkPrHBdkZLv/a2V09On+V3J4aPE/BfAJC8=",
+        "narHash": "sha256-4XLvuSIDZJGS17xEwSrNuJLL7UjDYKGJSbK1WWX2AK8=",
         "owner": "cachix",
         "repo": "git-hooks.nix",
-        "rev": "f3bb95498eaaa49a93bacaf196cdb6cf8e872cdf",
+        "rev": "e35aed5fda3cc79f88ed7f1795021e559582093a",
         "type": "github"
       },
       "original": {
@@ -122,21 +71,6 @@
         "nixpkgs-regression": "nixpkgs-regression",
         "pre-commit-hooks": "pre-commit-hooks"
       }
-    },
-    "systems": {
-      "locked": {
-        "lastModified": 1681028828,
-        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
-        "owner": "nix-systems",
-        "repo": "default",
-        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
-        "type": "github"
-      },
-      "original": {
-        "owner": "nix-systems",
-        "repo": "default",
-        "type": "github"
-      }
     }
   },
   "root": "root",

flake.nix

@@ -6,11 +6,7 @@
     nixpkgs-regression.url = "github:NixOS/nixpkgs/215d4d0fd80ca5163643b03a33fde804a29cc1e2";
     pre-commit-hooks = {
       url = "github:cachix/git-hooks.nix";
-      inputs = {
+      flake = false;
-        flake-compat.follows = "flake-compat";
-        nixpkgs.follows = "nixpkgs";
-        nixpkgs-stable.follows = "nixpkgs";
-      };
     };
     flake-compat = {
       url = "github:edolstra/flake-compat";
@@ -301,9 +297,22 @@
           );
         };
 
-        pre-commit = builtins.mapAttrs (
+        pre-commit = forAllSystems (
-          system: pre-commit-lib:
+          system:
-          pre-commit-lib.run {
+          let
+            pkgs = nixpkgsFor.${system}.native;
+            # Import pre-commit bypassing the flake because flakes don't let
+            # you have overlays. Also their implementation forces an
+            # unnecessary reimport of nixpkgs for our use cases.
+            tools = import (pre-commit-hooks + "/nix/call-tools.nix") pkgs;
+            pre-commit-run = pkgs.callPackage (pre-commit-hooks + "/nix/run.nix") {
+              inherit tools;
+              isFlakes = true;
+              # unused!
+              gitignore-nix-src = builtins.throw "gitignore-nix-src is unused";
+            };
+          in
+          pre-commit-run {
             src = self;
             hooks = {
               no-commit-to-branch = {
@@ -345,15 +354,11 @@
               };
               treefmt = {
                 enable = true;
-                settings.formatters =
+                settings.formatters = [ pkgs.nixfmt ];
-                  let
-                    pkgs = nixpkgsFor.${system}.native;
-                  in
-                  [ pkgs.nixfmt ];
               };
             };
           }
-        ) pre-commit-hooks.lib;
+        );
       };
 
       # NOTE *do not* add fresh derivations to checks, always add them to