Add latest commit hash to compare cache key

Adds the latest commit hash for a repository to the compare cache key.

Changelog: fixed

lib/api/repositories.rb

@@ -126,8 +126,9 @@ module API
       end
       get ':id/repository/compare' do
         ff_enabled = Feature.enabled?(:api_caching_rate_limit_repository_compare, user_project, default_enabled: :yaml)
+        cache_key = [user_project, user_project.repository.commit, :repository_compare, current_user, declared_params]
 
-        cache_action_if(ff_enabled, [user_project, :repository_compare, current_user, declared_params], expires_in: 1.minute) do
+        cache_action_if(ff_enabled, cache_key, expires_in: 1.minute) do
           if params[:from_project_id].present?
             target_project = MergeRequestTargetProjectFinder
               .new(current_user: current_user, source_project: user_project, project_feature: :repository)

spec/requests/api/repositories_spec.rb

@@ -495,6 +495,43 @@ RSpec.describe API::Repositories do
 
         expect(response).to have_gitlab_http_status(:not_found)
       end
+
+      it "returns a newly created commit", :use_clean_rails_redis_caching do
+        # Parse the commits ourselves because json_response is cached
+        def commit_messages(response)
+          Gitlab::Json.parse(response.body)["commits"].map do |commit|
+            commit["message"]
+          end
+        end
+
+        # First trigger the rate limit cache
+        get api(route, current_user), params: { from: 'master', to: 'feature' }
+
+        expect(response).to have_gitlab_http_status(:ok)
+        expect(commit_messages(response)).not_to include("Cool new commit")
+
+        # Then create a new commit via the API
+        post api("/projects/#{project.id}/repository/commits", user), params: {
+          branch: "feature",
+          commit_message: "Cool new commit",
+          actions: [
+            {
+              action: "create",
+              file_path: "foo/bar/baz.txt",
+              content: "puts 8"
+            }
+          ]
+        }
+
+        expect(response).to have_gitlab_http_status(:created)
+
+        # Now perform the same query as before, but the cache should have expired
+        # and our new commit should exist
+        get api(route, current_user), params: { from: 'master', to: 'feature' }
+
+        expect(response).to have_gitlab_http_status(:ok)
+        expect(commit_messages(response)).to include("Cool new commit")
+      end
     end
 
     context 'when unauthenticated', 'and project is public' do