Customize Start discussion message according to if the noteable can be resolvable

app/models/discussion_note.rb

 # A note in a non-diff discussion on an issue, merge request, commit, or snippet
 class DiscussionNote < Note
   NOTEABLE_TYPES = %w(MergeRequest Issue Commit Snippet).freeze
+  RESOLVABLE_TYPES = %w(MergeRequest).freeze
 
   validates :noteable_type, inclusion: { in: NOTEABLE_TYPES }
 

app/models/note.rb

@@ -228,6 +228,10 @@ class Note < ActiveRecord::Base
     DiscussionNote::NOTEABLE_TYPES.include?(self.noteable_type) && !part_of_discussion?
   end
 
+  def can_be_resolvable?
+    DiscussionNote::RESOLVABLE_TYPES.include?(self.noteable_type)
+  end
+
   def discussion_class(noteable = nil)
     # When commit notes are rendered on an MR's Discussion page, they are
     # displayed in one discussion instead of individually.

app/views/projects/notes/_comment_type_button.html.haml

+- noteable_type = @note.noteable_type
 .btn-group.append-right-10.comment-type-dropdown.js-comment-type-dropdown
   %button.btn.btn-nr.btn-create.comment-btn.js-comment-button.js-comment-submit-button
     Comment
@@ -9,10 +10,10 @@
         = icon('check')
         .description
           %strong Comment
-          %p= "Add a general comment to this #{@note.noteable_type.titleize.downcase}."
+          %p= "Add a general comment to this #{noteable_type.titleize.downcase}."
       %li.divider
       %li#discussion{ data: { value: 'DiscussionNote', 'button-text' => 'Start discussion', 'secondary-button-text' => 'Start discussion & close merge request' } }
         = icon('check')
         .description
           %strong Start discussion
-          %p Discuss a specific suggestion or question that needs to be resolved.
+          %p= "Discuss a specific suggestion or question#{@note.can_be_resolvable? ? ' that needs to be resolved' : ''}."