implemented using an ivar, and added specs

app/controllers/projects/commit_controller.rb

@@ -16,6 +16,8 @@ class Projects::CommitController < Projects::ApplicationController
   before_action :define_note_vars, only: [:show, :diff_for_path]
   before_action :authorize_edit_tree!, only: [:revert, :cherry_pick]
+  BRANCH_SEARCH_LIMIT = 1000
+
   def show
     apply_diff_view_cookie!
@@ -59,8 +61,11 @@ class Projects::CommitController < Projects::ApplicationController
     # branch_names_contains/tag_names_contains can take a long time when there are thousands of
     # branches/tags - each `git branch --contains xxx` request can consume a cpu core.
     # so only do the query when there are a manageable number of branches/tags
-    @branches = @project.repository.branch_count > 1000 ? [:limit_exceeded] : @project.repository.branch_names_contains(commit.id)
-    @tags = @project.repository.tag_count > 1000 ? [:limit_exceeded] : @project.repository.tag_names_contains(commit.id)
+    @branches_limit_exceeded = @project.repository.branch_count > BRANCH_SEARCH_LIMIT
+    @branches = @branches_limit_exceeded ? [] : @project.repository.branch_names_contains(commit.id)
+
+    @tags_limit_exceeded = @project.repository.tag_count > BRANCH_SEARCH_LIMIT
+    @tags = @tags_limit_exceeded ? [] : @project.repository.tag_names_contains(commit.id)
     render layout: false
   end

app/views/projects/commit/branches.html.haml

-- if @branches.any?
-  - branch = commit_default_branch(@project, @branches)
-  - if branch == :limit_exceeded
+- if @branches.any? || @branches_limit_exceeded
+  - if @branches_limit_exceeded
     = commit_branch_link('#', _('Too many branches to search'))
   - else
+    - branch = commit_default_branch(@project, @branches)
     = commit_branch_link(project_ref_path(@project, branch), branch)
 -# `commit_default_branch` deletes the default branch from `@branches`,
 -# so only render this if we have more branches or tags left
-- if @branches.any? || @tags.any?
+- if @branches.any? || @tags.any? || @tags_limit_exceeded
   %span
     = link_to "…", "#", class: "js-details-expand label label-gray"
     %span.js-details-content.hide
       = commit_branches_links(@project, @branches) if @branches.any?
-      - if @tags.first == :limit_exceeded
+      - if @tags_limit_exceeded
         = commit_tag_link('#', _('Too many tags to search'))
       - elsif @tags.any?
         = commit_tags_links(@project, @tags)

spec/controllers/projects/commit_controller_spec.rb

@@ -134,8 +134,8 @@ describe Projects::CommitController do
     end
   end
-  describe "GET branches" do
-    it "contains branch and tags information" do
+  describe 'GET branches' do
+    it 'contains branch and tags information' do
       commit = project.commit('5937ac0a7beb003549fc5fd26fc247adbce4a52e')
       get(:branches,
@@ -143,8 +143,26 @@ describe Projects::CommitController do
           project_id: project,
           id: commit.id)
-      expect(assigns(:branches)).to include("master", "feature_conflict")
-      expect(assigns(:tags)).to include("v1.1.0")
+      expect(assigns(:branches)).to include('master', 'feature_conflict')
+      expect(assigns(:branches_limit_exceeded)).to be_falsey
+      expect(assigns(:tags)).to include('v1.1.0')
+      expect(assigns(:tags_limit_exceeded)).to be_falsey
+    end
+
+    it 'returns :limit_exceeded when number of branches/tags reach a threshhold' do
+      commit = project.commit('5937ac0a7beb003549fc5fd26fc247adbce4a52e')
+      allow_any_instance_of(Repository).to receive(:branch_count).and_return(1001)
+      allow_any_instance_of(Repository).to receive(:tag_count).and_return(1001)
+
+      get(:branches,
+          namespace_id: project.namespace,
+          project_id: project,
+          id: commit.id)
+
+      expect(assigns(:branches)).to eq([])
+      expect(assigns(:branches_limit_exceeded)).to be_truthy
+      expect(assigns(:tags)).to eq([])
+      expect(assigns(:tags_limit_exceeded)).to be_truthy
     end
   end

spec/views/projects/commit/branches.html.haml_spec.rb

+require 'spec_helper'
+
+describe 'projects/commit/branches.html.haml' do
+  let(:project) { create(:project, :repository) }
+
+  before do
+    assign(:project, project)
+  end
+
+  context 'branches and tags' do
+    before do
+      assign(:branches, ['master', 'test-branch'])
+      assign(:branches_limit_exceeded, false)
+      assign(:tags, ['tag1'])
+      assign(:tags_limit_exceeded, false)
+
+      render
+    end
+
+    it 'shows branch and tag links' do
+      expect(rendered).to have_selector('.js-details-expand')
+      expect(rendered).to have_link('master')
+      expect(rendered).to have_link('test-branch')
+      expect(rendered).to have_link('tag1')
+    end
+  end
+
+  context 'throttled branches and tags' do
+    before do
+      assign(:branches, [])
+      assign(:branches_limit_exceeded, true)
+      assign(:tags, [])
+      assign(:tags_limit_exceeded, true)
+
+      render
+    end
+
+    it 'shows too many to search' do
+      expect(rendered).to have_selector('.js-details-expand')
+      expect(rendered).to have_link('Too many branches to search', href: '#')
+      expect(rendered).to have_link('Too many tags to search', href: '#')
+    end
+  end
+end