Cache issuable template names

We were looking these up on each request to an issue page, because the form is
pre-filled, as is the template dropdown. That was unnecessary: we could just
treat these as 'special' repository files (like the rendered README) and cache
them in Redis until they change on a push.

app/helpers/issuables_helper.rb

@@ -314,20 +314,12 @@ module IssuablesHelper
     @issuable_templates ||=
       case issuable
       when Issue
-        issue_template_names
+        ref_project.repository.issue_template_names
       when MergeRequest
-        merge_request_template_names
+        ref_project.repository.merge_request_template_names
       end
   end
-  def merge_request_template_names
-    @merge_request_templates ||= Gitlab::Template::MergeRequestTemplate.dropdown_names(ref_project)
-  end
-
-  def issue_template_names
-    @issue_templates ||= Gitlab::Template::IssueTemplate.dropdown_names(ref_project)
-  end
-
   def selected_template(issuable)
     params[:issuable_template] if issuable_templates(issuable).any? { |template| template[:name] == params[:issuable_template] }
   end

app/models/repository.rb

@@ -34,7 +34,8 @@ class Repository
   CACHED_METHODS = %i(size commit_count rendered_readme contribution_guide
                       changelog license_blob license_key gitignore koding_yml
                       gitlab_ci_yml branch_names tag_names branch_count
-                      tag_count avatar exists? empty? root_ref has_visible_content?).freeze
+                      tag_count avatar exists? empty? root_ref has_visible_content?
+                      issue_template_names merge_request_template_names).freeze
   # Methods that use cache_method but only memoize the value
   MEMOIZED_CACHED_METHODS = %i(license empty_repo?).freeze
@@ -50,7 +51,9 @@ class Repository
     gitignore: :gitignore,
     koding: :koding_yml,
     gitlab_ci: :gitlab_ci_yml,
-    avatar: :avatar
+    avatar: :avatar,
+    issue_template: :issue_template_names,
+    merge_request_template: :merge_request_template_names
   }.freeze
   # Wraps around the given method and caches its output in Redis and an instance
@@ -535,6 +538,16 @@ class Repository
   end
   cache_method :avatar
+  def issue_template_names
+    Gitlab::Template::IssueTemplate.dropdown_names(project)
+  end
+  cache_method :issue_template_names, fallback: []
+
+  def merge_request_template_names
+    Gitlab::Template::MergeRequestTemplate.dropdown_names(project)
+  end
+  cache_method :merge_request_template_names, fallback: []
+
   def readme
     if readme = tree(:head)&.readme
       ReadmeBlob.new(readme, self)

changelogs/unreleased/cache-issuable-template-names.yml

+---
+title: Cache issue and MR template names in Redis
+merge_request:
+author:
+type: other

lib/gitlab/file_detector.rb

@@ -12,6 +12,8 @@ module Gitlab
       contributing: /\Acontributing[^\/]*\z/i,
       version: 'version',
       avatar: /\Alogo\.(png|jpg|gif)\z/,
+      issue_template: /\A\.gitlab\/issue_templates\/[^\/]+\.md\z/,
+      merge_request_template: /\A\.gitlab\/merge_request_templates\/[^\/]+\.md\z/,
       # Configuration files
       gitignore: '.gitignore',

spec/lib/gitlab/file_detector_spec.rb

@@ -56,6 +56,14 @@ describe Gitlab::FileDetector do
       end
     end
+    it 'returns the type of an issue template' do
+      expect(described_class.type_of('.gitlab/issue_templates/foo.md')).to eq(:issue_template)
+    end
+
+    it 'returns the type of a merge request template' do
+      expect(described_class.type_of('.gitlab/merge_request_templates/foo.md')).to eq(:merge_request_template)
+    end
+
     it 'returns nil for an unknown file' do
       expect(described_class.type_of('foo.txt')).to be_nil
     end

spec/models/repository_spec.rb

@@ -1509,7 +1509,9 @@ describe Repository do
         :gitignore,
         :koding,
         :gitlab_ci,
-        :avatar
+        :avatar,
+        :issue_template,
+        :merge_request_template
       ])
       repository.after_change_head