Fix merge train unnecessarily retries pipeline by a race condition

This commit fixes the problem by evaluating in_progress_merge_sha.

app/services/merge_requests/merge_service.rb

@@ -79,6 +79,8 @@ module MergeRequests
       end
 
       merge_request.update!(merge_commit_sha: commit_id)
+    ensure
+      merge_request.update_column(:in_progress_merge_commit_sha, nil)
     end
 
     def try_merge
@@ -89,8 +91,6 @@ module MergeRequests
     rescue => e
       handle_merge_error(log_message: e.message)
       raise_error('Something went wrong during merge')
-    ensure
-      merge_request.update!(in_progress_merge_commit_sha: nil)
     end
 
     def after_merge

changelogs/unreleased/fix-merge-train-to-evaluate-in_progress_merge_commit_sha.yml

+---
+title: Fix merge train unnecessarily retries pipeline by a race condition
+merge_request: 24566
+author:
+type: fixed

ee/app/models/merge_train.rb

@@ -95,8 +95,9 @@ class MergeTrain < ApplicationRecord
     end
 
     def sha_exists_in_history?(target_project_id, target_branch, newrev, limit: 20)
-      MergeRequest.exists?(id: complete_merge_trains(target_project_id, target_branch, limit: limit),
-                           merge_commit_sha: newrev)
+      MergeRequest.where(id: complete_merge_trains(target_project_id, target_branch, limit: limit))
+                  .where('merge_commit_sha = ? OR in_progress_merge_commit_sha = ?', newrev, newrev)
+                  .exists?
     end
 
     def total_count_in_train(merge_request)

ee/spec/models/merge_train_spec.rb

@@ -263,7 +263,7 @@ describe MergeTrain do
         let!(:merge_request_1) { create_merge_request_on_train(status: :merging) }
 
         before do
-          merge_request_1.update_column(:merge_commit_sha, merge_commit_sha_1)
+          merge_request_1.update_column(:in_progress_merge_commit_sha, merge_commit_sha_1)
         end
 
         it { is_expected.to eq(true) }

spec/services/merge_requests/merge_service_spec.rb

@@ -31,6 +31,11 @@ describe MergeRequests::MergeService do
       it { expect(merge_request).to be_valid }
       it { expect(merge_request).to be_merged }
 
+      it 'persists merge_commit_sha and nullifies in_progress_merge_commit_sha' do
+        expect(merge_request.merge_commit_sha).not_to be_nil
+        expect(merge_request.in_progress_merge_commit_sha).to be_nil
+      end
+
       it 'sends email to user2 about merge of new merge_request' do
         email = ActionMailer::Base.deliveries.last
         expect(email.to.first).to eq(user2.email)