Fix bug with snippet updating error losing changes

app/services/snippets/update_service.rb

@@ -48,10 +48,12 @@ module Snippets
 
       true
     rescue => e
-      # Restore old attributes
+      # Restore old attributes but re-assign changes so they're not lost
       unless snippet.previous_changes.empty?
         snippet.previous_changes.each { |attr, value| snippet[attr] = value[0] }
         snippet.save
+
+        snippet.assign_attributes(params)
       end
 
       snippet.errors.add(:repository, 'Error updating the snippet')

changelogs/unreleased/vij-fix-update-bug.yml

+---
+title: Fix Snippet update error bug losing changes
+merge_request: 31873
+author:
+type: fixed

spec/services/snippets/update_service_spec.rb

@@ -196,14 +196,24 @@ describe Snippets::UpdateService do
         end
       end
 
-      it 'rolls back any snippet modifications' do
-        option_keys = options.stringify_keys.keys
-        orig_attrs = snippet.attributes.select { |k, v| k.in?(option_keys) }
+      context 'with snippet modifications' do
+        let(:option_keys) { options.stringify_keys.keys }
 
-        subject
+        it 'rolls back any snippet modifications' do
+          orig_attrs = snippet.attributes.select { |k, v| k.in?(option_keys) }
+
+          subject
+
+          persisted_attrs = snippet.reload.attributes.select { |k, v| k.in?(option_keys) }
+          expect(orig_attrs).to eq persisted_attrs
+        end
+
+        it 'keeps any snippet modifications' do
+          subject
 
-        current_attrs = snippet.attributes.select { |k, v| k.in?(option_keys) }
-        expect(orig_attrs).to eq current_attrs
+          instance_attrs = snippet.attributes.select { |k, v| k.in?(option_keys) }
+          expect(options.stringify_keys).to eq instance_attrs
+        end
       end
     end