Add script for creating a rollback changelog

.github/workflows/script/rollback_changelog.py

@@ -0,0 +1,62 @@
+import datetime
+import os
+import sys
+
+EMPTY_CHANGELOG = """# CodeQL Action Changelog
+
+"""
+
+def get_today_string():
+  today = datetime.datetime.today()
+  return '{:%d %b %Y}'.format(today)
+
+# Include everything up to and after the first heading,
+# but not the first heading and body.
+def drop_unreleased_section(lines: list[str]):
+  before_first_section = ''
+  after_first_section = ''
+  found_first_section = False
+  skipped_first_section = False
+
+  for i, line in enumerate(lines):
+    if line.startswith('## ') and not found_first_section:
+      found_first_section = True
+    elif line.startswith('## ') and found_first_section:
+      skipped_first_section = True
+
+    if not found_first_section:
+      before_first_section += line
+    if skipped_first_section:
+      after_first_section += line
+
+  return (before_first_section, after_first_section)
+
+def update_changelog(target_version, rollback_version, new_version):
+  before_first_section = EMPTY_CHANGELOG
+  after_first_section = ''
+
+  if (os.path.exists('CHANGELOG.md')):
+    with open('CHANGELOG.md', 'r') as f:
+      (before_first_section, after_first_section) = drop_unreleased_section(f.readlines())
+
+  newHeader = f'## {new_version} - {get_today_string()}\n'
+
+  print(before_first_section, end="")
+  print(newHeader)
+  print(f"This release rolls back {rollback_version} due to issues with that release. It is identical to {target_version}.\n")
+  print(after_first_section)
+
+# We expect three version strings as input:
+#
+# - target_version: the version that we are re-releasing as `new_version`
+# - rollback_version: the version that we are rolling back, typically the one that followed `target_version`
+# - new_version: the new version that we are releasing `target_version` as, typically the one that follows `rollback_version`
+#
+# Example: python3 .github/workflows/script/rollback_changelog.py "1.2.3" "1.2.4" "1.2.5"
+if len(sys.argv) < 4:
+  raise Exception('Expecting argument: target_version rollback_version new_version')
+
+target_version = sys.argv[1]
+rollback_version = sys.argv[2]
+new_version = sys.argv[3]
+update_changelog(target_version, rollback_version, new_version)