Added optional for Todo state

cf. https://gitlab.com/gitlab-org/gitlab/merge_requests/16837#note_217807588

app/finders/todos_finder.rb

@@ -47,11 +47,12 @@ class TodosFinder
     sort(items)
   end
 
-  # Returns `true` if the current user has any todos for the given target.
+  # Returns `true` if the current user has any todos for the given target with the optional given state.
   #
   # target - The value of the `target_type` column, such as `Issue`.
-  def any_for_target?(target)
-    current_user.todos.any_for_target?(target)
+  # state - The value of the `state` column, such as `pending` or `done`.
+  def any_for_target?(target, *state)
+    current_user.todos.any_for_target?(target, state)
   end
 
   private

app/models/todo.rb

@@ -89,11 +89,12 @@ class Todo < ApplicationRecord
       ])
     end
 
-    # Returns `true` if the current user has any todos for the given target.
+    # Returns `true` if the current user has any todos for the given target with the optional given state.
     #
     # target - The value of the `target_type` column, such as `Issue`.
-    def any_for_target?(target)
-      exists?(target: target, state: :pending)
+    # state - The value of the `state` column, such as `pending` or `done`.
+    def any_for_target?(target, *state)
+      state.empty? ? exists?(target: target) : exists?(target: target, state: state)
     end
 
     # Updates the state of a relation of todos to the new state.

app/services/todo_service.rb

@@ -191,7 +191,7 @@ class TodoService
   end
 
   def todo_exist?(issuable, current_user)
-    TodosFinder.new(current_user).any_for_target?(issuable)
+    TodosFinder.new(current_user).any_for_target?(issuable, :pending)
   end
 
   private

spec/models/todo_spec.rb

@@ -281,12 +281,12 @@ describe Todo do
       expect(described_class.any_for_target?(issue)).to eq(true)
     end
 
-    it 'returns false if there are only todos for a given target with state done' do
+    it 'returns false if there are only todos for a given target with state done while searching for pending' do
       issue = create(:issue)
       create(:todo, state: :done, target: issue)
       create(:todo, state: :done, target: issue)
 
-      expect(described_class.any_for_target?(issue)).to eq(false)
+      expect(described_class.any_for_target?(issue, :pending)).to eq(false)
     end
 
     it 'returns false if there are no todos for a given target' do