Fixes to serverless patch script (#2175)

.github/workflows/serverless-patch.sh

@@ -0,0 +1,38 @@
+#!/usr/bin/env bash
+
+set -exuo pipefail
+
+merge_commit_sha=$(jq -r '.pull_request.merge_commit_sha' "$GITHUB_EVENT_PATH")
+pull_request_id=$(jq -r '.pull_request.number' "$GITHUB_EVENT_PATH")
+
+# generate patch file
+cd "$GITHUB_WORKSPACE/elasticsearch-js"
+git format-patch -1 --stdout "$merge_commit_sha" > /tmp/patch.diff
+
+# apply patch file
+cd "$GITHUB_WORKSPACE/elasticsearch-serverless-js"
+git checkout -b "apply-patch-$pull_request_id"
+git apply -C1 --recount --reject /tmp/patch.diff || exit 0
+
+comment="Patch applied from elastic/elasticsearch-js#$pull_request_id"
+
+# check for rejected patches
+tick='\`' # just trying to satisfy shellcheck here
+has_rejects=''
+for f in ./**/*.rej; do
+  has_rejects=' --draft'
+  comment="$comment
+
+## Rejected patch $tick$f$tick must be resolved:
+
+$tick$tick$tick
+$(cat "$f")
+$tick$tick$tick
+"
+done
+
+# open a PR
+gh pr create \
+  -t "Apply PR changes from elastic/elasticsearch-js#$pull_request_id" \
+  --body "$comment" \
+  "$has_rejects"

.github/workflows/serverless-patch.yml

@@ -36,17 +36,5 @@ jobs:
           repository: elastic/elasticsearch-serverless-js
           ref: main
           path: elasticsearch-serverless-js
-      - name: Generate patch file
-        run: |
-          cd $GITHUB_WORKSPACE/elasticsearch-js
-          git format-patch -1 --stdout ${{ github.event.pull_request.merge_commit_sha }} > /tmp/patch.diff
-      - name: Apply patch file
-        run: |
-          cd $GITHUB_WORKSPACE/elasticsearch-serverless-js
-          git checkout -b apply-patch-${{ github.event.pull_request.id }}
-          git apply -C1 --recount --reject /tmp/patch.diff || exit 0
-          comment='Patch applied from elastic/elasticsearch-js#${{ github.event.pull_request.id }}'
-          for f in $(find . -name '*.rej'); do
-            comment="$comment\n\n## Rejected patch \`$f`\:\n\`\`\`\n$(cat $f)\n\`\`\`"
-          done
-          gh pr create -t "Apply PR changes from elastic/elasticsearch-js#${{ github.event.pull_request.id }}" --body "$comment"
+      - name: Apply patch from stack to serverless
+        run: ./.github/serverless-patch.sh