devshell: add (tiny) but useful pre-commit hook

devshell.toml

@@ -1,10 +1,17 @@
+imports = [ "git.hooks" ]
+
 [devshell]
 name = "nixpkgs"
 packages = [
   "fd",
   "nixpkgs-fmt",
+  "editorconfig-checker",
 ]
 
+[[commands]]
+package = "editorconfig-checker"
+category = "linters"
+
 [[commands]]
 name = "fmt"
 help = "Check Nix formatting"
@@ -17,3 +24,34 @@ help = "Check Nix parsing"
 category = "folder tree checks"
 command = "fd --extension nix --exec nix-instantiate --parse --quiet {} >/dev/null"
 
+[git.hooks]
+enable = true
+pre-commit.text = """
+#!/usr/bin/env bash
+set -eou pipefail
+if git rev-parse --verify HEAD >/dev/null 2>&1
+then
+  against=HEAD
+else
+  # Initial commit: diff against an empty tree object
+  against=$(${git}/bin/git hash-object -t tree /dev/null)
+fi
+
+diff="git diff-index --name-only --cached $against --diff-filter d"
+
+nix_files=($($diff -- '*.nix'))
+all_files=($($diff))
+
+# Format staged nix files.
+if [[ -n "${nix_files[@]}" ]]; then
+  nixpkgs-fmt "${nix_files[@]}"
+  git add "${nix_files[@]}"
+fi
+
+# check editorconfig
+if ! editorconfig-checker -- "${all_files[@]}"; then
+  echo -e "\nCode is not aligned with .editorconfig
+Review the output and commit your fixes" >&2
+  exit 1
+fi
+"""