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.

9 files changed, 111 insertions, 78 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'
diff --git a/app/finders/issuable_finder.rb b/app/finders/issuable_finder.rb
index 0fe3000ca01..384a336e2bb 100644
--- a/app/finders/issuable_finder.rb
+++ b/app/finders/issuable_finder.rb
@@ -25,32 +25,38 @@ class IssuableFinder
 
   NONE = '0'.freeze
 
-  SCALAR_PARAMS = %i[
-    assignee_id
-    assignee_username
-    author_id
-    author_username
-    authorized_only
-    due_date
-    group_id
-    iids
-    label_name
-    milestone_title
-    my_reaction_emoji
-    non_archived
-    project_id
-    scope
-    search
-    sort
-    state
-    include_subgroups
-  ].freeze
-  ARRAY_PARAMS = { label_name: [], iids: [], assignee_username: [] }.freeze
-
-  VALID_PARAMS = (SCALAR_PARAMS + [ARRAY_PARAMS]).freeze
-
   attr_accessor :current_user, :params
 
+  def self.scalar_params
+    @scalar_params ||= %i[
+      assignee_id
+      assignee_username
+      author_id
+      author_username
+      authorized_only
+      group_id
+      iids
+      label_name
+      milestone_title
+      my_reaction_emoji
+      non_archived
+      project_id
+      scope
+      search
+      sort
+      state
+      include_subgroups
+    ]
+  end
+
+  def self.array_params
+    @array_params ||= { label_name: [], iids: [], assignee_username: [] }
+  end
+
+  def self.valid_params
+    @valid_params ||= scalar_params + [array_params]
+  end
+
   def initialize(current_user, params = {})
     @current_user = current_user
     @params = params
@@ -58,6 +64,15 @@ class IssuableFinder
 
   def execute
     items = init_collection
+    items = filter_items(items)
+
+    # Filtering by project HAS TO be the last because we use the project IDs yielded by the issuable query thus far
+    items = by_project(items)
+
+    sort(items)
+  end
+
+  def filter_items(items)
     items = by_scope(items)
     items = by_created_at(items)
     items = by_state(items)
@@ -65,16 +80,11 @@ class IssuableFinder
     items = by_search(items)
     items = by_assignee(items)
     items = by_author(items)
-    items = by_due_date(items)
     items = by_non_archived(items)
     items = by_iids(items)
     items = by_milestone(items)
     items = by_label(items)
-    items = by_my_reaction_emoji(items)
-
-    # Filtering by project HAS TO be the last because we use the project IDs yielded by the issuable query thus far
-    items = by_project(items)
-    sort(items)
+    by_my_reaction_emoji(items)
   end
 
   def find(*params)
@@ -396,42 +406,6 @@ class IssuableFinder
     items
   end
 
-  def by_due_date(items)
-    if due_date?
-      if filter_by_no_due_date?
-        items = items.without_due_date
-      elsif filter_by_overdue?
-        items = items.due_before(Date.today)
-      elsif filter_by_due_this_week?
-        items = items.due_between(Date.today.beginning_of_week, Date.today.end_of_week)
-      elsif filter_by_due_this_month?
-        items = items.due_between(Date.today.beginning_of_month, Date.today.end_of_month)
-      end
-    end
-
-    items
-  end
-
-  def filter_by_no_due_date?
-    due_date? && params[:due_date] == Issue::NoDueDate.name
-  end
-
-  def filter_by_overdue?
-    due_date? && params[:due_date] == Issue::Overdue.name
-  end
-
-  def filter_by_due_this_week?
-    due_date? && params[:due_date] == Issue::DueThisWeek.name
-  end
-
-  def filter_by_due_this_month?
-    due_date? && params[:due_date] == Issue::DueThisMonth.name
-  end
-
-  def due_date?
-    params[:due_date].present? && klass.column_names.include?('due_date')
-  end
-
   def label_names
     if labels?
       params[:label_name].is_a?(String) ? params[:label_name].split(',') : params[:label_name]
diff --git a/app/finders/issues_finder.rb b/app/finders/issues_finder.rb
index 83245aadf6e..d65c620e75a 100644
--- a/app/finders/issues_finder.rb
+++ b/app/finders/issues_finder.rb
@@ -16,10 +16,15 @@
 #     sort: string
 #     my_reaction_emoji: string
 #     public_only: boolean
+#     due_date: date or '0', '', 'overdue', 'week', or 'month'
 #
 class IssuesFinder < IssuableFinder
   CONFIDENTIAL_ACCESS_LEVEL = Gitlab::Access::REPORTER
 
+  def self.scalar_params
+    @scalar_params ||= super + [:due_date]
+  end
+
   def klass
     Issue.includes(:author)
   end
@@ -52,6 +57,46 @@ class IssuesFinder < IssuableFinder
     params.fetch(:public_only, false)
   end
 
+  def filter_items(items)
+    by_due_date(super)
+  end
+
+  def by_due_date(items)
+    if due_date?
+      if filter_by_no_due_date?
+        items = items.without_due_date
+      elsif filter_by_overdue?
+        items = items.due_before(Date.today)
+      elsif filter_by_due_this_week?
+        items = items.due_between(Date.today.beginning_of_week, Date.today.end_of_week)
+      elsif filter_by_due_this_month?
+        items = items.due_between(Date.today.beginning_of_month, Date.today.end_of_month)
+      end
+    end
+
+    items
+  end
+
+  def filter_by_no_due_date?
+    due_date? && params[:due_date] == Issue::NoDueDate.name
+  end
+
+  def filter_by_overdue?
+    due_date? && params[:due_date] == Issue::Overdue.name
+  end
+
+  def filter_by_due_this_week?
+    due_date? && params[:due_date] == Issue::DueThisWeek.name
+  end
+
+  def filter_by_due_this_month?
+    due_date? && params[:due_date] == Issue::DueThisMonth.name
+  end
+
+  def due_date?
+    params[:due_date].present?
+  end
+
   def user_can_see_all_confidential_issues?
     return @user_can_see_all_confidential_issues if defined?(@user_can_see_all_confidential_issues)
 
diff --git a/spec/controllers/concerns/issuable_collections_spec.rb b/spec/controllers/concerns/issuable_collections_spec.rb
index d7825364ed5..c1f42bbb9d7 100644
--- a/spec/controllers/concerns/issuable_collections_spec.rb
+++ b/spec/controllers/concerns/issuable_collections_spec.rb
@@ -8,6 +8,10 @@ describe IssuableCollections do
       def self.helper_method(name); end
 
       include IssuableCollections
+
+      def finder_type
+        IssuesFinder
+      end
     end
 
     controller = klass.new