Cache only the user defined metrics dashboard paths

- Currently, the output of the #all_dashboard_paths method of all
dashboard services is collected and cached by the Repository model.
Unfortunately, this cache cannot be deleted when an update is made to
the #all_dashboard_paths method.

- This MR changes the Repository model cache to only contain a list of
user-defined dashboard paths under .gitlab/dashboards. The
all_dashboard_paths methods do not do any other expensive operations
(other than fetching a list of dashboards under .gitlab/dashboards).

- This change should remove the need to delete the cache when a change
is made to the all_dashboard_paths method.

app/models/repository.rb

@@ -43,7 +43,7 @@ class Repository
                       gitlab_ci_yml branch_names tag_names branch_count
                       tag_count avatar exists? root_ref merged_branch_names
                       has_visible_content? issue_template_names merge_request_template_names
-                      metrics_dashboard_paths xcode_project?).freeze
+                      user_defined_metrics_dashboard_paths xcode_project?).freeze
 
   # Methods that use cache_method but only memoize the value
   MEMOIZED_CACHED_METHODS = %i(license).freeze
@@ -61,7 +61,7 @@ class Repository
     avatar: :avatar,
     issue_template: :issue_template_names,
     merge_request_template: :merge_request_template_names,
-    metrics_dashboard: :metrics_dashboard_paths,
+    metrics_dashboard: :user_defined_metrics_dashboard_paths,
     xcode_config: :xcode_project?
   }.freeze
 
@@ -576,10 +576,10 @@ class Repository
   end
   cache_method :merge_request_template_names, fallback: []
 
-  def metrics_dashboard_paths
+  def user_defined_metrics_dashboard_paths
     Gitlab::Metrics::Dashboard::Finder.find_all_paths_from_source(project)
   end
-  cache_method :metrics_dashboard_paths
+  cache_method :user_defined_metrics_dashboard_paths, fallback: []
 
   def readme
     head_tree&.readme

app/services/metrics/dashboard/custom_dashboard_service.rb

@@ -7,6 +7,7 @@ module Metrics
   module Dashboard
     class CustomDashboardService < ::Metrics::Dashboard::BaseService
       DASHBOARD_ROOT = ".gitlab/dashboards"
+      DASHBOARD_EXTENSION = '.yml'
 
       class << self
         def valid_params?(params)
@@ -14,8 +15,7 @@ module Metrics
         end
 
         def all_dashboard_paths(project)
-          file_finder(project)
-            .list_files_for(DASHBOARD_ROOT)
+          project.repository.user_defined_metrics_dashboard_paths
             .map do |filepath|
               {
                 path: filepath,
@@ -28,7 +28,7 @@ module Metrics
         end
 
         def file_finder(project)
-          Gitlab::Template::Finders::RepoTemplateFinder.new(project, DASHBOARD_ROOT, '.yml')
+          Gitlab::Template::Finders::RepoTemplateFinder.new(project, DASHBOARD_ROOT, DASHBOARD_EXTENSION)
         end
 
         # Grabs the filepath after the base directory.

lib/gitlab/metrics/dashboard/finder.rb

@@ -72,17 +72,20 @@ module Gitlab
           #                              display_name: String,
           #                              default: Boolean }]
           def find_all_paths(project)
-            project.repository.metrics_dashboard_paths
+            user_facing_dashboard_services(project).flat_map do |service|
+              service.all_dashboard_paths(project)
+            end
           end
 
-          # Summary of all known dashboards. Used to populate repo cache.
+          # Returns list of all user-defined dashboard paths. Used to populate repo cache.
+          # Also deletes all dashboard cache entries.
           # Prefer #find_all_paths.
+          # @return [Array] ex) ['.gitlab/dashboards/dashboard1.yml']
           def find_all_paths_from_source(project)
             Gitlab::Metrics::Dashboard::Cache.delete_all!
 
-            user_facing_dashboard_services(project).flat_map do |service|
-              service.all_dashboard_paths(project)
-            end
+            file_finder(project)
+              .list_files_for(::Metrics::Dashboard::CustomDashboardService::DASHBOARD_ROOT)
           end
 
           private
@@ -102,6 +105,14 @@ module Gitlab
             predefined_dashboard_services
           end
 
+          def file_finder(project)
+            Gitlab::Template::Finders::RepoTemplateFinder.new(
+              project,
+              ::Metrics::Dashboard::CustomDashboardService::DASHBOARD_ROOT,
+              ::Metrics::Dashboard::CustomDashboardService::DASHBOARD_EXTENSION
+            )
+          end
+
           def predefined_dashboard_services
             ::Metrics::Dashboard::PredefinedDashboardService.descendants - PREDEFINED_DASHBOARD_EXCLUSION_LIST
           end

spec/models/repository_spec.rb

@@ -1926,7 +1926,7 @@ RSpec.describe Repository do
         :has_visible_content?,
         :issue_template_names,
         :merge_request_template_names,
-        :metrics_dashboard_paths,
+        :user_defined_metrics_dashboard_paths,
         :xcode_project?
       ])
 

spec/services/metrics/dashboard/custom_dashboard_service_spec.rb

@@ -104,6 +104,15 @@ RSpec.describe Metrics::Dashboard::CustomDashboardService, :use_clean_rails_memo
           }]
         )
       end
+
+      it 'caches repo file list' do
+        expect(Gitlab::Template::Finders::RepoTemplateFinder).to receive(:new)
+          .once
+          .and_call_original
+
+        described_class.all_dashboard_paths(project)
+        described_class.all_dashboard_paths(project)
+      end
     end
   end