Add pre-commit config

.circleci/config.yml

@@ -24,6 +24,9 @@ jobs:
       - run:
           name: install dependencies
           command: opam exec -- make setup
+      - run:
+          name: check code formatting
+          command: ./scripts/lint
       - run:
           name: build
           command: opam exec -- make

.pre-commit-config.yaml

@@ -0,0 +1,12 @@
+repos:
+  - repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v3.3.0
+    hooks:
+      - id: check-yaml
+      - id: end-of-file-fixer
+      - id: trailing-whitespace
+
+  - repo: https://github.com/returntocorp/pre-commit-ocaml
+    rev: v1.0.0
+    hooks:
+      - id: ocp-indent

Makefile

@@ -25,6 +25,7 @@ setup:
 	./scripts/check-prerequisites
 	./scripts/install-tree-sitter-cli
 	opam install --deps-only -y .
+	opam install ocp-indent
 
 # Shortcut for updating the git submodules.
 .PHONY: update

scripts/lint

@@ -0,0 +1,32 @@
+#! /usr/bin/env bash
+#
+# Check that the user ran the pre-commit hooks.
+#
+set -eu
+
+eval $(opam env)
+
+pre-commit install
+if ! pre-commit run --all; then
+  cat <<EOF
+It looks like the user who committed the code did not set up their
+pre-commit hook. You need the following one-time setup:
+
+  1. Install the 'pre-commit' command:
+
+       $ pip3 install pre-commit
+
+  2. Install the pre-commit hooks for the repo:
+
+       $ pre-commit install
+
+  3. Install ocp-indent:
+
+       $ opam install ocp-indent
+
+  4. To fix already committed code, run:
+
+       $ pre-commit run --all
+EOF
+  exit 1
+fi