flake.nix: init

default.nix

@@ -5,13 +5,15 @@ in
   system ? builtins.currentSystem,
   nixpkgs ? sources.nixpkgs,
   treefmt-nix ? sources.treefmt-nix,
+  pkgs ? (
+    import nixpkgs {
+      inherit system;
+      config = { };
+      overlays = [ ];
+    }
+  ),
 }:
 let
-  pkgs = import nixpkgs {
-    inherit system;
-    config = { };
-    overlays = [ ];
-  };
   inherit (pkgs) lib;
 
   runtimeExprPath = ./src/eval.nix;
@@ -79,10 +81,30 @@ let
       }
     );
 
+    # Fits in with `nix fmt`.
+    treefmtWrapper = treefmtEval.config.build.wrapper;
+
     # Run regularly by CI and turned into a PR
     autoPrUpdate =
       let
         updateScripts = {
+          flake = pkgs.writeShellApplication {
+            name = "update-flake";
+            runtimeInputs = with pkgs; [
+              git
+              nix
+            ];
+            text = ''
+              echo "<details><summary>flake.nix changes</summary>"
+              # Needed because GitHub's rendering of the first body line breaks down otherwise
+              echo ""
+              echo '```'
+              cd "$1"
+              nix flake update 2>&1
+              echo  '```'
+              echo "</details>"
+            '';
+          };
           npins = pkgs.writeShellApplication {
             name = "update-npins";
             runtimeInputs = with pkgs; [ npins ];
@@ -91,7 +113,7 @@ let
               # Needed because GitHub's rendering of the first body line breaks down otherwise
               echo ""
               echo '```'
-              npins update --directory "$1/npins" 2>&1
+              npins --directory "$1/npins" import-flake 2>&1
               echo  '```'
               echo "</details>"
             '';

flake.nix

@@ -0,0 +1,52 @@
+{
+  description = "nixpkgs-check-by-name: a linter for nixpkgs";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs";
+    treefmt-nix.url = "github:numtide/treefmt-nix";
+    treefmt-nix.inputs.nixpkgs.follows = "nixpkgs";
+  };
+
+  outputs =
+    {
+      self,
+      nixpkgs,
+      treefmt-nix,
+    }:
+    let
+      # Until https://github.com/NixOS/nixpkgs/pull/295083 is accepted and merged.
+      systems = [
+        "x86_64-linux"
+        "aarch64-linux"
+        "x86_64-darwin"
+        "aarch64-darwin"
+      ];
+      eachSystem =
+        f:
+        nixpkgs.lib.genAttrs systems (
+          system:
+          f (
+            import ./default.nix {
+              inherit nixpkgs system treefmt-nix;
+              pkgs = nixpkgs.legacyPackages.${system};
+            }
+          )
+        );
+    in
+    {
+      packages = eachSystem (this: {
+        default = this.build;
+      });
+
+      devShells = eachSystem (this: {
+        default = this.shell;
+      });
+
+      checks = eachSystem (this: {
+        formatting = this.treefmt;
+        nixpkgs = this.nixpkgsCheck;
+      });
+
+      formatter = eachSystem (this: this.treefmtWrapper);
+    };
+}