Add limit to recent_diff_head_shas as an argument

app/finders/ci/pipelines_for_merge_request_finder.rb

@@ -14,7 +14,7 @@ module Ci
 
     attr_reader :merge_request, :current_user
 
-    delegate :merge_request_diffs, :commit_shas, :target_project, :source_project, :source_branch, to: :merge_request
+    delegate :recent_diff_head_shas, :commit_shas, :target_project, :source_project, :source_branch, to: :merge_request
 
     # Fetch all pipelines that the user can read.
     def execute
@@ -84,7 +84,7 @@ module Ci
     def all_pipelines_for_merge_request
       if Feature.enabled?(:decomposed_ci_query_in_pipelines_for_merge_request_finder, source_project, default_enabled: :yaml)
         pipelines_for_merge_request = triggered_by_merge_request
-        pipelines_for_branch = triggered_for_branch.for_sha(recent_diff_head_shas)
+        pipelines_for_branch = triggered_for_branch.for_sha(recent_diff_head_shas(COMMITS_LIMIT))
 
         Ci::Pipeline.from_union([pipelines_for_merge_request, pipelines_for_branch])
       else
@@ -92,11 +92,6 @@ module Ci
       end
     end
 
-    def recent_diff_head_shas
-      # We're limiting the number of commits' SHAs to 100 since they are used in a WHERE clause of a query
-      merge_request_diffs.recent.limit(COMMITS_LIMIT).pluck(:head_commit_sha).uniq # rubocop: disable CodeReuse/ActiveRecord
-    end
-
     # NOTE: this method returns only parent merge request pipelines.
     # Child merge request pipelines have a different source.
     def triggered_by_merge_request

app/models/merge_request.rb

@@ -1658,8 +1658,8 @@ class MergeRequest < ApplicationRecord
     service_class.new(project, current_user, id: id, report_type: report_type).execute(comparison_base_pipeline(identifier), actual_head_pipeline)
   end
 
-  def recent_diff_head_shas
-    merge_request_diffs.recent.pluck(:head_commit_sha)
+  def recent_diff_head_shas(limit = 100)
+    merge_request_diffs.recent(limit).pluck(:head_commit_sha)
   end
 
   def all_commits

app/models/merge_request_diff.rb

@@ -66,7 +66,7 @@ class MergeRequestDiff < ApplicationRecord
     joins(:merge_request).where(merge_requests: { target_project_id: project_id })
   end
 
-  scope :recent, -> { order(id: :desc).limit(100) }
+  scope :recent, -> (limit = 100) { order(id: :desc).limit(limit) }
 
   scope :files_in_database, -> do
     where(stored_externally: [false, nil]).where(arel_table[:files_count].gt(0))