add CI action that requires clean merges between all named branches

Author: sam0x17

.github/workflows/require-clean-merges.yml

@@ -0,0 +1,46 @@
+name: Require Clean Merges
+
+on:
+  pull_request:
+    branches:
+      - devnet-ready
+      - devnet
+      - testnet
+
+jobs:
+  assert-clean-merges:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout Repository
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0 # Ensures we get all branches for merging
+
+      - name: Determine Target Branch and Set Merge List
+        id: set-merge-branches
+        run: |
+          TARGET_BRANCH="${{ github.event.pull_request.base.ref }}"
+          if [[ "$TARGET_BRANCH" == "devnet-ready" ]]; then
+            echo "MERGE_BRANCHES=devnet-ready devnet testnet main" >> $GITHUB_ENV
+          elif [[ "$TARGET_BRANCH" == "devnet" ]]; then
+            echo "MERGE_BRANCHES=devnet testnet main" >> $GITHUB_ENV
+          elif [[ "$TARGET_BRANCH" == "testnet" ]]; then
+            echo "MERGE_BRANCHES=testnet main" >> $GITHUB_ENV
+          elif [[ "$TARGET_BRANCH" == "main" ]]; then
+            echo "MERGE_BRANCHES=main" >> $GITHUB_ENV
+          else
+            echo "MERGE_BRANCHES=devnet-ready devnet testnet main" >> $GITHUB_ENV"
+          fi
+
+      - name: Check Merge Cleanliness
+        run: |
+          for branch in $MERGE_BRANCHES; do
+            echo "Checking merge from $branch into ${{ github.event.pull_request.base.ref }}..."
+            git fetch origin $branch
+            git checkout ${{ github.event.pull_request.base.ref }}
+            if ! git merge --no-commit --no-ff origin/$branch; then
+              echo "Merge conflict detected when merging $branch into ${{ github.event.pull_request.base.ref }}"
+              exit 1
+            fi
+            git merge --abort
+          done