Add experimental nightly changelog workflow

Author: matejsemancik

.github/workflows/nightly-changelog.yml

@@ -0,0 +1,82 @@
+name: Nightly Changelog
+
+on:
+  push:
+    branches:
+      - feature/nightlies
+  workflow_call:
+    inputs:
+      branch:
+        description: 'Branch to check for changes'
+        required: false
+        type: string
+        default: 'develop'
+    outputs:
+      has_changes:
+        description: "True if there were changes"
+        value: ${{ jobs.changelog.outputs.has_changes }}
+      changelog:
+        description: "The changelog"
+        value: ${{ jobs.changelog.outputs.changelog }}
+
+jobs:
+  changelog:
+    runs-on: ubuntu-latest
+    outputs:
+      has_changes: ${{ steps.changelog.outputs.has_changes }}
+      changelog: ${{ steps.changelog.outputs.changelog }}
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0 # Fetch all history for all branches and tags
+
+      - name: Restore last commit SHA from cache
+        id: cache-commit-sha
+        uses: actions/cache@v4
+        with:
+          path: last_commit_sha.txt
+          # A unique key is used to force a cache miss and trigger a save post-job.
+          key: last-commit-sha-${{ github.repository }}-${{ inputs.branch }}-${{ github.run_id }}
+          # The most recent cache is restored using a partial key match.
+          restore-keys: |
+            last-commit-sha-${{ github.repository }}-${{ inputs.branch }}-
+
+      - name: Generate changelog
+        id: changelog
+        run: |
+          # Get the SHA of the latest commit on the branch
+          CURRENT_COMMIT_SHA=$(git rev-parse origin/${{ inputs.branch }})
+
+          # Get the previously cached SHA. If the file doesn't exist, the variable will be empty.
+          LAST_COMMIT_SHA=$(cat last_commit_sha.txt 2>/dev/null || echo "")
+
+          # If no SHA was restored, fall back to a time-based comparison.
+          if [ -z "$LAST_COMMIT_SHA" ]; then
+            echo "No valid cache found. Comparing against the last 24 hours."
+            COMMIT_LOG=$(git log origin/${{ inputs.branch }} --since="24 hours ago" --pretty=format:"%s")
+          else
+            echo "Valid cache found. Comparing against commit $LAST_COMMIT_SHA."
+            COMMIT_LOG=$(git log $LAST_COMMIT_SHA..$CURRENT_COMMIT_SHA --pretty=format:"%s")
+          fi
+
+          # Set outputs
+          if [ -z "$COMMIT_LOG" ]; then
+            echo "has_changes=false" >> $GITHUB_OUTPUT
+            echo "changelog=" >> $GITHUB_OUTPUT
+          else
+            echo "has_changes=true" >> $GITHUB_OUTPUT
+            echo "changelog<<EOF" >> $GITHUB_OUTPUT
+            echo "$COMMIT_LOG" >> $GITHUB_OUTPUT
+            echo "EOF" >> $GITHUB_OUTPUT
+          fi
+
+          # Overwrite the local file with the new SHA to be cached post-job.
+          echo $CURRENT_COMMIT_SHA > last_commit_sha.txt
+
+      - name: Debug Outputs
+        if: always()
+        run: |
+          echo "Debug Outputs:"
+          echo "has_changes: ${{ steps.changelog.outputs.has_changes }}"
+          echo "changelog: ${{ steps.changelog.outputs.changelog }}"