Refactor IssuableFinder to extract model-specific logicrefactor-issuable-finder-to-use-inheritance

By extracting a new `filter_items` method, we can override that in the
IssuesFinder and MergeRequestsFinder separately, so we don't need checks that
the model is the correct one, because we can just use the class we're in to know
that.

We can do the same for the VALID_PARAMS constant, by making it a class method.

6 files changed, 22 insertions, 12 deletions

diff --git a/app/controllers/concerns/issuable_collections.rb b/app/controllers/concerns/issuable_collections.rb
index 0d7ee06deb6..f7ba305a59f 100644
--- a/app/controllers/concerns/issuable_collections.rb
+++ b/app/controllers/concerns/issuable_collections.rb
@@ -103,7 +103,7 @@ module IssuableCollections
       # @filter_params[:authorized_only] = true
     end
 
-    @filter_params.permit(IssuableFinder::VALID_PARAMS)
+    @filter_params.permit(finder_type.valid_params)
   end
   # rubocop:enable Gitlab/ModuleWithInstanceVariables
 
@@ -146,7 +146,7 @@ module IssuableCollections
 
   def finder
     strong_memoize(:finder) do
-      issuable_finder_for(@finder_type) # rubocop:disable Gitlab/ModuleWithInstanceVariables
+      issuable_finder_for(finder_type)
     end
   end
 
diff --git a/app/controllers/concerns/issues_action.rb b/app/controllers/concerns/issues_action.rb
index 3ba1235cee0..3b11a373368 100644
--- a/app/controllers/concerns/issues_action.rb
+++ b/app/controllers/concerns/issues_action.rb
@@ -4,7 +4,6 @@ module IssuesAction
 
   # rubocop:disable Gitlab/ModuleWithInstanceVariables
   def issues
-    @finder_type = IssuesFinder
     @issues = issuables_collection
               .non_archived
               .page(params[:page])
@@ -17,4 +16,11 @@ module IssuesAction
     end
   end
   # rubocop:enable Gitlab/ModuleWithInstanceVariables
+
+  private
+
+  def finder_type
+    (super if defined?(super)) ||
+      (IssuesFinder if action_name == 'issues')
+  end
 end
diff --git a/app/controllers/concerns/merge_requests_action.rb b/app/controllers/concerns/merge_requests_action.rb
index a9cc13038bf..b70db99b157 100644
--- a/app/controllers/concerns/merge_requests_action.rb
+++ b/app/controllers/concerns/merge_requests_action.rb
@@ -4,8 +4,6 @@ module MergeRequestsAction
 
   # rubocop:disable Gitlab/ModuleWithInstanceVariables
   def merge_requests
-    @finder_type = MergeRequestsFinder
-
     @merge_requests = issuables_collection.page(params[:page])
 
     @issuable_meta_data = issuable_meta_data(@merge_requests, collection_type)
@@ -14,6 +12,11 @@ module MergeRequestsAction
 
   private
 
+  def finder_type
+    (super if defined?(super)) ||
+      (MergeRequestsFinder if action_name == 'merge_requests')
+  end
+
   def filter_params
     super.merge(non_archived: true)
   end
diff --git a/app/controllers/projects/issues_controller.rb b/app/controllers/projects/issues_controller.rb
index 33fced99132..73806454525 100644
--- a/app/controllers/projects/issues_controller.rb
+++ b/app/controllers/projects/issues_controller.rb
@@ -243,9 +243,8 @@ class Projects::IssuesController < Projects::ApplicationController
     Issues::UpdateService.new(project, current_user, update_params)
   end
 
-  def set_issuables_index
-    @finder_type = IssuesFinder
-    super
+  def finder_type
+    IssuesFinder
   end
 
   def whitelist_query_limiting
diff --git a/app/controllers/projects/merge_requests_controller.rb b/app/controllers/projects/merge_requests_controller.rb
index 8eed957d9fe..a1af125547c 100644
--- a/app/controllers/projects/merge_requests_controller.rb
+++ b/app/controllers/projects/merge_requests_controller.rb
@@ -323,9 +323,8 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
     @target_branches = @merge_request.target_project.repository.branch_names
   end
 
-  def set_issuables_index
-    @finder_type = MergeRequestsFinder
-    super
+  def finder_type
+    MergeRequestsFinder
   end
 
   def check_user_can_push_to_source_branch!
diff --git a/app/controllers/projects_controller.rb b/app/controllers/projects_controller.rb
index 72573e0765d..0370edc6e20 100644
--- a/app/controllers/projects_controller.rb
+++ b/app/controllers/projects_controller.rb
@@ -279,7 +279,6 @@ class ProjectsController < Projects::ApplicationController
         @project_wiki = @project.wiki
         @wiki_home = @project_wiki.find_page('home', params[:version_id])
       elsif @project.feature_available?(:issues, current_user)
-        @finder_type = IssuesFinder
         @issues = issuables_collection.page(params[:page])
         @collection_type = 'Issue'
         @issuable_meta_data = issuable_meta_data(@issues, @collection_type)
@@ -289,6 +288,10 @@ class ProjectsController < Projects::ApplicationController
     end
   end
 
+  def finder_type
+    IssuesFinder
+  end
+
   def determine_layout
     if [:new, :create].include?(action_name.to_sym)
       'application'