Devops: Add script to update CHANGELOG.md

Add a script that generates a bullet-point list of all the commits since the
last release tag along with a default set of headers to sort them in. A link
to the commit is added at the end of each item. This script:

1. Removes a lot of busy-work related to preparing the `CHANGELOG.md` for a
   release.
2. Standardises the headers we use to sort the commits for the `CHANGELOG.md`

.github/workflows/update_changelog.py

@@ -0,0 +1,86 @@
+#!/bin/bash
+# -*- coding: utf-8 -*-
+"""Script for automatically updating the `CHANGELOG.md` based on the commits since the latest release tag."""
+from pathlib import Path
+import re
+import subprocess
+
+DEFAULT_CHANGELOG_SECTIONS = """
+### ‼️ Breaking changes
+
+
+### ✨ New features
+
+
+### 🗑️ Deprecations
+
+
+### 👌 Improvements
+
+
+### 🐛 Bug fixes
+
+
+### 📚 Documentation
+
+
+### 🔧 Maintenance
+
+
+### ⬆️ Update dependencies
+
+
+### ♻️ Refactor
+
+"""
+
+
+def update_changelog():
+    """Update the `CHANGELOG.md` for a first draft of the release."""
+
+    print('🔍 Checking the current version number')
+    current_changelog = Path('CHANGELOG.md').read_text(encoding='utf-8')
+
+    from aiida_quantumespresso import __version__
+
+    if str(__version__) in current_changelog:
+        print('🛑 Current version already in `CHANGELOG.md`. Skipping...')
+        return
+
+    print('⬆️ Found updated version number, adapting `CHANGELOG.md`.')
+    tags = subprocess.run(['git', 'tag', '--sort=v:refname'], capture_output=True, check=True, encoding='utf-8').stdout
+    latest_tag = re.findall(r'(v\d\.\d\.\d)\n', tags)[-1]
+
+    print(f'🔄 Comparing with latest tag `{latest_tag}`.')
+    commits = subprocess.run(['git', 'log', "--pretty=format:'%h|%H|%s'", f'{latest_tag}..origin/main'],
+                             capture_output=True,
+                             check=True,
+                             encoding='utf-8').stdout
+
+    pr_pattern = re.compile(r'\(\S(?P<pr_number>\d+)\)')
+
+    changelog_message = f'## v{__version__}\n' + DEFAULT_CHANGELOG_SECTIONS
+
+    for commit in commits.splitlines():
+
+        # Remove the PR number from the commit message
+        pr_match = pr_pattern.search(commit)
+
+        if pr_match is not None:
+            pr_number = pr_match.groupdict()['pr_number']
+            commit = commit.replace(fr'(#{pr_number})', '')
+
+        # Add the commit hash (short) to link to the changelog
+        commit = commit.strip("'")
+        hash_short, hash_long, message = commit.split('|', maxsplit=2)
+        message += f'[[{hash_short}](https://github.com/aiidateam/aiida-quantumespresso/commit/{hash_long})]'
+        changelog_message += f'\n* {message}'
+
+    with Path('CHANGELOG.md').open('w', encoding='utf8') as handle:
+        handle.write(changelog_message + '\n\n' + current_changelog)
+
+    print("🚀 Success! Finalise the `CHANGELOG.md` and let's get this baby released.")
+
+
+if __name__ == '__main__':
+    update_changelog()