chore: add commit message format requirements

Refs HAUKI-602

.pre-commit-config.yaml

@@ -1,5 +1,7 @@
 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
@@ -23,3 +25,9 @@ repos:
     hooks:
       - id: isort
         args: [--check]
+  - 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

@@ -45,7 +45,7 @@ docker compose up dev
 
 and open your browser to http://127.0.0.1:8000/.
 
-Run tests with 
+Run tests with
 
 ```
 docker compose run dev test
@@ -104,7 +104,7 @@ pip install -r requirements.txt
 pip install -r requirements-dev.txt
 ```
 
-Copy the development config file example `config_dev.env.example` to `config_dev.env` 
+Copy the development config file example `config_dev.env.example` to `config_dev.env`
 (feel free to edit the configuration file if you have any settings you wish to change):
 ```
 cp config_dev.env.example config_dev.env
@@ -129,7 +129,7 @@ and open your browser to http://127.0.0.1:8000/.
 #### Pre-commit hooks
 
 Before committing files to the repository it's advisable to use the configured pre-commit hooks (see [`.pre-commit-config.yaml`](./.pre-commit-config.yaml)). The CI pipeline will fail if the files are not formatted correctly.
- 
+
 pre-commit is included in the requirements-dev.txt. After cloning the repository you should install the requirements and then install the hooks by running:
 
 ```
@@ -144,6 +144,14 @@ You can at any time run the following command if you would like to check all of
 pre-commit run --all-files
 ```
 
+## 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.
+
 ## Importing data
 
 Currently, importing *resources* from Helsinki metropolitan area unit registry (TPREK) is supported. Import all resources from [TPREK API](https://www.hel.fi/palvelukarttaws/restpages/ver4.html) by
@@ -167,7 +175,7 @@ Import library opening hours from the kirjastot.fi API for all resources that ha
 python manage.py hours_import kirjastot --openings
 ```
 
-This imports opening hours for the libraries starting from today and ending one year in the future. If you wish to specify another start date, you may use 
+This imports opening hours for the libraries starting from today and ending one year in the future. If you wish to specify another start date, you may use
 
 ```
 python manage.py hours_import kirjastot --openings --date 2021-01-01

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;