Add treefmt

And use it in place of editorconfig/nixpkgs-fmt checks

.editorconfig

@@ -1,24 +0,0 @@
-# top-most EditorConfig file
-root = true
-
-# Unix-style newlines with a newline ending every file
-[*]
-charset = utf-8
-end_of_line = lf
-insert_final_newline = true
-trim_trailing_whitespace = true
-
-[*.{cc,hh,hpp,pl,pm,sh,t}]
-indent_style = space
-intend_size = 4
-
-[Makefile]
-indent_style = tab
-
-[*.nix]
-indent_style = space
-indent_size = 2
-
-# Match diffs, avoid to trim trailing whitespace
-[*.{diff,patch}]
-trim_trailing_whitespace = false

flake.nix

@@ -8,6 +8,7 @@
     flake-utils.lib.eachDefaultSystem (system:
       let
         pkgs = nixpkgs.legacyPackages.${system};
+        inherit (pkgs) stdenv;
         drvArgs = { srcDir = self; };
       in
       rec {
@@ -26,25 +27,18 @@
           in
           {
 
-            editorconfig = pkgs.runCommand "editorconfig-check"
-              {
-                nativeBuildInputs = [
-                  pkgs.editorconfig-checker
-                ];
-              } ''
-              editorconfig-checker ${self}
-              touch $out
+            treefmt = stdenv.mkDerivation {
+              name = "treefmt-check";
+              src = self;
+              nativeBuildInputs = devShells.default.nativeBuildInputs;
+              dontConfigure = true;
+
+              buildPhase = ''
+                env HOME=$(mktemp -d) treefmt --fail-on-change
               '';
 
-            nixpkgs-fmt = pkgs.runCommand "fmt-check"
-              {
-                nativeBuildInputs = [
-                  pkgs.nixpkgs-fmt
-                ];
-              } ''
-              nixpkgs-fmt --check .
-              touch $out
-            '';
+              installPhase = "touch $out";
+            };
 
             build = mkVariant pkgs.nix;
             build-unstable = mkVariant pkgs.nixUnstable;

shell.nix

@@ -26,8 +26,7 @@ in
 
   nativeBuildInputs = old.nativeBuildInputs ++ [
 
-    pkgs.editorconfig-checker
-
+    pkgs.treefmt
     pkgs.nixpkgs-fmt
 
     (pkgs.python3.withPackages (ps: [

tests/assets/ci.nix

@@ -1,6 +1,5 @@
-{
-  pkgs ? import (builtins.getFlake (toString ./.)).inputs.nixpkgs { }
-  , system ? pkgs.system
+{ pkgs ? import (builtins.getFlake (toString ./.)).inputs.nixpkgs { }
+, system ? pkgs.system
 }:
 
 {

treefmt.toml

@@ -0,0 +1,3 @@
+[formatter.nix]
+command = "nixpkgs-fmt"
+includes = ["*.nix"]