From 7c213baf4d83b1e3f90fee9894f87433944ff94b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mariusz=20J=C3=B3zala?=
 <377355+jozala@users.noreply.github.com>
Date: Fri, 27 Jun 2025 12:50:36 +0200
Subject: [PATCH] [CI] Correct the way merge base is identified (#130175)

Without fetching, the local repository might be missing reference to the
base branch, causing git merge-base to fail.
---
 .buildkite/scripts/run-pr-upgrade-tests.sh | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/.buildkite/scripts/run-pr-upgrade-tests.sh b/.buildkite/scripts/run-pr-upgrade-tests.sh
index 1cbfdfc99152..14e659c08ee9 100644
--- a/.buildkite/scripts/run-pr-upgrade-tests.sh
+++ b/.buildkite/scripts/run-pr-upgrade-tests.sh
@@ -18,7 +18,8 @@ fi
 
 # Identify the merge base of the current commit (branch) and the base branch of the pull request.
 # PR upgrade tests are run from the merge base to the current commit.
-BASE_COMMIT=$(git merge-base $BUILDKITE_PULL_REQUEST_BASE_BRANCH $BUILDKITE_COMMIT)
+git fetch origin $BUILDKITE_PULL_REQUEST_BASE_BRANCH
+BASE_COMMIT=$(git merge-base origin/$BUILDKITE_PULL_REQUEST_BASE_BRANCH $BUILDKITE_COMMIT)
 
 VERSION=$(sed -n 's/^elasticsearch[[:space:]]*=[[:space:]]*\(.*\)/\1/p' build-tools-internal/version.properties)