Add a partial changelog when releasing

.github/workflows/post-release-mergeback.yml

@@ -151,13 +151,24 @@ jobs:
             --assignee "${GITHUB_ACTOR}" \
             --draft
 
+
+      - name: Prepare the partial Changelog
+        env:
+          VERSION: "${{ steps.getVersion.outputs.version }}"
+          PARTIAL_CHANGELOG: "${{ runner.temp }}/partial_changelog.md"
+        run: |
+          # Prepare the partial changelog for the release notes
+          python .github/workflows/script/prepare_changelog.py CHANGELOG.md "$VERSION"> $PARTIAL_CHANGELOG
+
       - name: Create the GitHub release
         env:
           VERSION: "${{ steps.getVersion.outputs.version }}"
+          PARTIAL_CHANGELOG: "${{ runner.temp }}/partial_changelog.md"
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
           # Do not mark this release as latest. The most recent CLI release must be marked as latest.
           gh release create \
-            "${VERSION}" \
+            "$VERSION" \
             --latest=false \
-            -t "${VERSION}" \
-            -F CHANGELOG.md
+            -t "$VERSION" \
+            -F "$PARTIAL_CHANGELOG"

.github/workflows/script/prepare_changelog.py

@@ -0,0 +1,37 @@
+import os
+import sys
+
+EMPTY_CHANGELOG = 'No changes.\n\n'
+
+# Prepare the changelog for the new release
+# This function will extract the part of the changelog that
+# we want to include in the new release.
+def extract_changelog_snippet(changelog_file, version_tag):
+  output = ''
+  if (not os.path.exists(changelog_file)):
+    output = EMPTY_CHANGELOG
+
+  else:
+    with open('CHANGELOG.md', 'r') as f:
+      lines = f.readlines()
+
+      # Include everything up to, but excluding the second heading
+      found_first_section = False
+      for i, line in enumerate(lines):
+        if line.startswith('## '):
+          if found_first_section:
+            break
+          found_first_section = True
+        output += line
+
+  output += f"See the full [CHANGELOG.md](https://github.com/github/codeql-action/blob/{version_tag}/CHANGELOG.md) for more information."
+
+  return output
+
+
+if len(sys.argv) < 3:
+  raise Exception('Expecting argument: changelog_file version_tag')
+changelog_file = sys.argv[1]
+version_tag = sys.argv[2]
+
+print(extract_changelog_snippet(changelog_file, version_tag))