Filter by `None`/`Any` for labels in issues/mrs API

By using the parameters `?labels=None|Any` the user can filter
issues/mrs from the API that has `none/any` label.

Affected endpoints are:

- /api/issues
- /api/projects/:id/issues
- /api/groups/:id/issues
- /api/merge_requests
- /api/projects/:id/merge_requests
- /api/groups/:id/merge_requests

3 files changed, 13 insertions, 8 deletions

diff --git a/app/finders/issuable_finder.rb b/app/finders/issuable_finder.rb
index fdc630cbf72..e04e3a2a7e0 100644
--- a/app/finders/issuable_finder.rb
+++ b/app/finders/issuable_finder.rb
@@ -210,7 +210,14 @@ class IssuableFinder
   end
 
   def filter_by_no_label?
-    labels? && params[:label_name].include?(Label::None.title)
+    downcased = label_names.map(&:downcase)
+
+    # Label::NONE is deprecated and should be removed in 12.0
+    downcased.include?(FILTER_NONE) || downcased.include?(Label::NONE)
+  end
+
+  def filter_by_any_label?
+    label_names.map(&:downcase).include?(FILTER_ANY)
   end
 
   def labels
@@ -465,6 +472,8 @@ class IssuableFinder
     items =
       if filter_by_no_label?
         items.without_label
+      elsif filter_by_any_label?
+        items.any_label
       else
         items.with_label(label_names, params[:sort])
       end
diff --git a/app/models/concerns/issuable.rb b/app/models/concerns/issuable.rb
index 69c5affe142..5080fe03cc8 100644
--- a/app/models/concerns/issuable.rb
+++ b/app/models/concerns/issuable.rb
@@ -90,6 +90,7 @@ module Issuable
     scope :order_milestone_due_asc,  -> { left_joins_milestones.reorder('milestones.due_date IS NULL, milestones.id IS NULL, milestones.due_date ASC') }
 
     scope :without_label, -> { joins("LEFT OUTER JOIN label_links ON label_links.target_type = '#{name}' AND label_links.target_id = #{table_name}.id").where(label_links: { id: nil }) }
+    scope :any_label, -> { joins(:label_links).group(:id) }
     scope :join_project, -> { joins(:project) }
     scope :inc_notes_with_associations, -> { includes(notes: [:project, :author, :award_emoji]) }
     scope :references_project, -> { references(:project) }
diff --git a/app/models/label.rb b/app/models/label.rb
index 165e4a8f3e5..5d2d1afd1d9 100644
--- a/app/models/label.rb
+++ b/app/models/label.rb
@@ -9,15 +9,10 @@ class Label < ActiveRecord::Base
   include Sortable
   include FromUnion
 
-  # Represents a "No Label" state used for filtering Issues and Merge
-  # Requests that have no label assigned.
-  LabelStruct = Struct.new(:title, :name)
-  None = LabelStruct.new('No Label', 'No Label')
-  Any = LabelStruct.new('Any Label', '')
-
   cache_markdown_field :description, pipeline: :single_line
 
-  DEFAULT_COLOR = '#428BCA'.freeze
+  DEFAULT_COLOR = '#428BCA'
+  NONE = 'no label'
 
   default_value_for :color, DEFAULT_COLOR