Use better message in merge to maintenance

.github/workflows/checks.yml

@@ -166,9 +166,6 @@ jobs:
           git remote add upstream https://github.com/${{ github.repository }}
           git fetch --no-tags upstream main maintenance
 
-          # This is its own command so that if the current branch is `maintenance` it'll be overridden.
-          git checkout -B maintenance upstream/maintenance
-
           baseRef="${{github.head_ref}}"
           before=""
 
@@ -180,17 +177,22 @@ jobs:
 
           range="$before..${{ github.event.pull_request.head.sha || github.event.after }}"
 
-          echo "Checking if $range can be cherry-picked onto the maintenance branch."
+          echo "Checking if $range can be applied onto the maintenance branch."
+
+          git fetch --no-tags origin maintenance main
+
+          branchName=$(git branch --show-current)
 
-          # Using cherry-pick preserves the history of the commits so it's normally ideal.
-          git cherry-pick --allow-empty --no-commit -m 1 "$range" || (
-            git cherry-pick --abort
-            echo "Cannot cherry-pick onto the maintenance branch! Will try git apply."
-          )
+          # Commit using the GitHub Actions bot user.
+          git config user.name "github-actions[bot]"
+          git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
 
-          # But if an intermediary commit fails to merge cleanly then cherry-pick fails.
-          # So use a 3-way merge to apply the changes.
-          git diff c33b7c566118dfc9179a66d312f5ef36bb8a5167..526a3c747d76c1b2f61221ec56ed1e132b5e416e | git apply --3wa
+          # Make the history linear to main again.
+          git rebase -X theirs origin/main
+
+          git checkout -B maintenance upstream/maintenance
+
+          git diff "origin/main..$branchName" | git apply --3way <<< "$diff"
 
       - name: Install Node
         if: steps.should_skip.outputs.should_skip != 'true'
@@ -230,33 +232,27 @@ jobs:
           fetch-depth: 0
           fetch-tags: false
 
-      - name: Cherry pick commits onto maintenance
+      - name: Pick commits onto maintenance
         run: |
-          git fetch origin maintenance:maintenance
+          git fetch --no-tags origin maintenance main
 
-          git switch maintenance
+          branchName=$(git branch --show-current)
 
           # Commit using the GitHub Actions bot user.
           git config user.name "github-actions[bot]"
           git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
 
-          range="${{ github.event.before }}..${{ github.event.after }}"
+          # Make the history linear to main again.
+          git rebase -X theirs origin/main
 
-          echo "Cherry picking $range onto the maintenance branch."
+          git checkout -B maintenance upstream/maintenance
 
-          # Pick the freshly added commits onto the maintenance branch.
-          if git cherry-pick --allow-empty -m 1 "$range"; then
-            exit 1
-          else
-            git cherry-pick --abort
-            echo "Falling back to 3way apply!"
-          fi
+          git diff "origin/main..$branchName" | git apply --3way
 
-          git diff c33b7c566118dfc9179a66d312f5ef36bb8a5167..526a3c747d76c1b2f61221ec56ed1e132b5e416e | git apply --3wa || (
-            echo "Both cherry-pick and 3way apply failed! This can only happen if there is a bug in checkCanMergeToMaintenance or mergeToMaintenance or someone pushed in between!" && exit 1
-          )
+          message=$(git log --format='* %s' A..B)
+          message="Merge $branchName into maintenance\n\n$message"
 
-          git commit -m "Applied c33b7c566118dfc9179a66d312f5ef36bb8a5167..526a3c747d76c1b2f61221ec56ed1e132b5e416e"
+          git commit -m "$message"
 
       - name: Push changes
         uses: ad-m/github-push-action@master