From a45cb6bf103b0734a988263507d3babb3009421c Mon Sep 17 00:00:00 2001
From: Brian Seeders <brian.seeders@elastic.co>
Date: Fri, 6 Oct 2023 11:52:16 -0400
Subject: [PATCH] [buildkite] Fix backport PR pipeline generation (#100427)

(cherry picked from commit f4d53bcc6102891374c670b61ed7d5b3ab5e47c3)
---
 .buildkite/scripts/pull-request/pipeline.ts | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/.buildkite/scripts/pull-request/pipeline.ts b/.buildkite/scripts/pull-request/pipeline.ts
index c4e12f2aa48fe..a6a3df6ff2aff 100644
--- a/.buildkite/scripts/pull-request/pipeline.ts
+++ b/.buildkite/scripts/pull-request/pipeline.ts
@@ -116,7 +116,10 @@ export const generatePipelines = (
     .filter((x) => x);
 
   if (!changedFiles?.length) {
-    const mergeBase = execSync(`git merge-base ${process.env["GITHUB_PR_TARGET_BRANCH"]} HEAD`, { cwd: PROJECT_ROOT })
+    const mergeBase = execSync(
+      `git fetch origin ${process.env["GITHUB_PR_TARGET_BRANCH"]}; git merge-base origin/${process.env["GITHUB_PR_TARGET_BRANCH"]} HEAD`,
+      { cwd: PROJECT_ROOT }
+    )
       .toString()
       .trim();