1 files changed, 21 insertions, 10 deletions
diff --git a/app/services/merge_requests/merge_service.rb b/app/services/merge_requests/merge_service.rb
index 70a67baa01c..449997bcf07 100644
--- a/app/services/merge_requests/merge_service.rb
+++ b/app/services/merge_requests/merge_service.rb
@@ -8,6 +8,8 @@ module MergeRequests
   # Executed when you do merge via GitLab UI
   #
   class MergeService < MergeRequests::BaseService
+    include Gitlab::Utils::StrongMemoize
+
     MergeError = Class.new(StandardError)
 
     attr_reader :merge_request, :source
@@ -37,15 +39,10 @@ module MergeRequests
     end
 
     def source
-      return merge_request.diff_head_sha unless merge_request.squash
-
-      squash_result = ::MergeRequests::SquashService.new(project, current_user, params).execute(merge_request)
-
-      case squash_result[:status]
-      when :success
-        squash_result[:squash_sha]
-      when :error
-        raise ::MergeRequests::MergeService::MergeError, squash_result[:message]
+      if merge_request.squash
+        squash_sha!
+      else
+        merge_request.diff_head_sha
       end
     end
 
@@ -82,8 +79,22 @@ module MergeRequests
       merge_request.update!(merge_commit_sha: commit_id)
     end
 
+    def squash_sha!
+      strong_memoize(:squash_sha) do
+        params[:merge_request] = merge_request
+        squash_result = ::MergeRequests::SquashService.new(project, current_user, params).execute
+
+        case squash_result[:status]
+        when :success
+          squash_result[:squash_sha]
+        when :error
+          raise ::MergeRequests::MergeService::MergeError, squash_result[:message]
+        end
+      end
+    end
+
     def try_merge
-      message = params[:commit_message] || merge_request.merge_commit_message
+      message = params[:commit_message] || merge_request.default_merge_commit_message
 
       repository.merge(current_user, source, merge_request, message)
     rescue Gitlab::Git::PreReceiveError => e