build: add commit message format requirements

From now on, all new commit messages must adhere to the conventional
commits v1.0.0 spec and their max line length is limited to 72
characters. The rules are enforced with commitlint, which is run as a
pre-commit hook and also as a stage in the GitHub CI pipeline.

.github/workflows/ci.yml

@@ -98,6 +98,9 @@ jobs:
           linters: isort
           run: isort . --check-only --diff
 
+      - name: Check commitlint
+        uses: wagoid/commitlint-github-action@0d749a1a91d4770e983a7b8f83d4a3f0e7e0874e  # v5.4.4
+
       # With pytest-cov use: --cov=.
       # Some errors, skipping --doctest-modules for now
       - name: Run tests

.pre-commit-config.yaml

@@ -1,6 +1,8 @@
 # Keep tool versions in sync with the versions in requirements-dev.txt
 default_language_version:
     python: python3
+default_install_hook_types: [pre-commit, commit-msg]
+default_stages: [pre-commit, manual]
 repos:
   - repo: https://github.com/pre-commit/pre-commit-hooks
     rev: v4.5.0
@@ -25,3 +27,9 @@ repos:
     hooks:
       - id: isort
         exclude: "migrations"
+  - repo: https://github.com/alessandrojcm/commitlint-pre-commit-hook
+    rev: v9.10.0
+    hooks:
+      - id: commitlint
+        stages: [commit-msg, manual]
+        additional_dependencies: ["@commitlint/config-conventional"]

README.md

@@ -281,6 +281,15 @@ git config blame.ignoreRevsFile .git-blame-ignore-revs
 ```
 
 
+## Commit message format
+
+New commit messages must adhere to the [Conventional Commits](https://www.conventionalcommits.org/)
+specification, and line length is limited to 72 characters.
+
+When [`pre-commit`](https://pre-commit.com/) is in use, [`commitlint`](https://github.com/conventional-changelog/commitlint)
+checks new commit messages for the correct format.
+
+
 ## Search
 
 Linkedevents uses Elasticsearch for generating results on the /search-endpoint. If you wish to use that functionality, proceed like so:

commitlint.config.js

@@ -0,0 +1,10 @@
+const Configuration = {
+  extends: ['@commitlint/config-conventional'],
+  rules: {
+    'header-max-length': [2, 'always', 72],
+    'body-max-line-length': [2, 'always', 72],
+    'body-leading-blank': [2, 'always'],
+  },
+};
+
+module.exports = Configuration;