chore: add treefmt formatting (nix fmt + pre-commit + CI check)

.github/workflows/ci.yml

@@ -24,4 +24,7 @@ jobs:
  run: if [ -f scripts/test ]; then nix develop -c bash ./scripts/test; fi
 
  - name: Luacheck
- run: nix develop -c luacheck --quiet --std lua51 --no-unused-args src/
+ run: nix develop -c luacheck --quiet --std lua51 --no-unused-args --max-line-length 130 src/
+
+ - name: Format check
+ run: nix fmt && git diff --exit-code

.gitignore

@@ -1,4 +1,6 @@
 /.*
 !/.gitignore
 !/.github/
+!/.tidyrc.json
+!/.lua-format
 /output/

.lua-format

@@ -0,0 +1,10 @@
+# LuaFormatter config for the hand-written FFI under src/.
+# 2-space indent. Keep simple functions on one line; column_limit sits a few
+# columns under luacheck's 130 limit because lua-format under-counts the leading
+# indent and trailing comma, so this keeps every emitted line within 130.
+indent_width: 2
+use_tab: false
+column_limit: 126
+continuation_indent_width: 2
+keep_simple_function_one_line: true
+keep_simple_control_block_one_line: true

.tidyrc.json

@@ -0,0 +1,10 @@
+{
+ "importSort": "source",
+ "importWrap": "source",
+ "indent": 2,
+ "operatorsFile": null,
+ "ribbon": 1,
+ "typeArrowPlacement": "first",
+ "unicode": "source",
+ "width": 80
+}

AGENTS.md

@@ -4,11 +4,21 @@ A PureScript→Lua FFI fork in the [`purescript-lua`](https://github.com/purescr
 
 ## Commands
 
-All commands run inside the nix dev shell:
-
 - Build: `nix develop -c ./scripts/build`
 - Test (only if the fork has `scripts/test`): `nix develop -c bash ./scripts/test`
-- Lint: `nix develop -c luacheck --quiet --std lua51 --no-unused-args src/`
+- Lint: `nix develop -c luacheck --quiet --std lua51 --no-unused-args --max-line-length 130 src/`
+- Format: `nix fmt` (check: `nix fmt && git diff --exit-code`)
+
+## Formatting
+
+`nix fmt` runs treefmt (`treefmt.nix`): nixfmt for Nix, `dhall format`, purs-tidy
+for `*.purs` (config in `.tidyrc.json`), and LuaFormatter for the `*.lua` FFI
+(config in `.lua-format`). LuaFormatter is used over StyLua because it keeps the
+parentheses pslua's foreign-file parser requires. The Lua line budget is 130
+columns, matching the `luacheck --max-line-length` above. The check is
+content-based (`nix fmt && git diff --exit-code`) rather than `treefmt --ci`,
+since the in-place formatters bump mtime even when content is unchanged, which
+trips treefmt's `--fail-on-change`. CI and the pre-commit hook use it.
 
 ## Lua 5.1 target
 

flake.nix

@@ -9,16 +9,33 @@
  inputs.nixpkgs.follows = "nixpkgs";
  };
  pslua.url = "github:purescript-lua/purescript-lua";
+ treefmt-nix = {
+ url = "github:numtide/treefmt-nix";
+ inputs.nixpkgs.follows = "nixpkgs";
+ };
  };
 
- outputs = { self, nixpkgs, flake-utils, purescript-overlay, pslua }:
- flake-utils.lib.eachDefaultSystem (system:
+ outputs =
+ {
+ self,
+ nixpkgs,
+ flake-utils,
+ purescript-overlay,
+ pslua,
+ treefmt-nix,
+ }:
+ flake-utils.lib.eachDefaultSystem (
+ system:
  let
  pkgs = import nixpkgs {
  inherit system;
  overlays = [ purescript-overlay.overlays.default ];
  };
- in {
+ treefmtEval = treefmt-nix.lib.evalModule pkgs ./treefmt.nix;
+ in
+ {
+ formatter = treefmtEval.config.build.wrapper;
+ checks.formatting = treefmtEval.config.build.check self;
  devShell = pkgs.mkShell {
  buildInputs = with pkgs; [
  dhall
@@ -31,8 +48,26 @@
  spago-bin.spago-0_21_0
  treefmt
  ];
+ # Install a content-based pre-commit hook. It compares the working
+ # tree diff before and after `nix fmt`, so it only objects to changes
+ # the formatter itself introduces (not the developer's existing
+ # unstaged work) and is not fooled by formatters that only bump mtime.
+ # Rewritten each shell entry to stay in sync with this flake.
+ shellHook = ''
+ hook=.git/hooks/pre-commit
+ if [ -d .git ]; then
+ printf '%s\n' \
+ '#!/usr/bin/env bash' \
+ 'before=$(git diff)' \
+ 'nix fmt >/dev/null 2>&1 || exit 0' \
+ '[ "$before" = "$(git diff)" ] || { echo "nix fmt changed files; re-stage them, then commit." >&2; exit 1; }' \
+ > "$hook"
+ chmod +x "$hook"
+ fi
+ '';
  };
- });
+ }
+ );
 
  # --- Flake Local Nix Configuration ----------------------------
  nixConfig = {

src/Effect/Exception.purs

@@ -12,8 +12,7 @@ module Effect.Exception
  , throw
  , throwException
  , try
- )
- where
+ ) where
 
 import Prelude
 

treefmt.nix

@@ -0,0 +1,43 @@
+{ pkgs, ... }:
+{
+ projectRootFile = "flake.nix";
+
+ # Nix — RFC 166 formatter.
+ programs.nixfmt.enable = true;
+
+ # Dhall — spago.dhall / packages.dhall layout.
+ programs.dhall.enable = true;
+
+ # PureScript — purs-tidy is not a first-class treefmt program, so wire it via
+ # the generic mechanism. It picks up `.tidyrc.json` from the project root.
+ settings.formatter.purs-tidy = {
+ command = "${pkgs.purs-tidy}/bin/purs-tidy";
+ options = [ "format-in-place" ];
+ includes = [ "*.purs" ];
+ };
+
+ # Lua FFI — LuaFormatter keeps the parentheses pslua's foreign-file parser
+ # requires (unlike StyLua, which strips them). Config in `.lua-format`.
+ settings.formatter.lua-format = {
+ command = "${pkgs.luaformatter}/bin/lua-format";
+ options = [
+ "-i"
+ "-c"
+ ".lua-format"
+ ];
+ includes = [ "*.lua" ];
+ };
+
+ # Never format generated output or vendored trees.
+ settings.global.excludes = [
+ "dist/*"
+ "output/*"
+ ".spago/*"
+ "node_modules/*"
+ "*.lock"
+ "flake.lock"
+ "spago.lock"
+ ".tidyrc.json"
+ ".lua-format"
+ ];
+}