FIX: Return next bookmarks page only if it exists (#18139)

It used to return the next URL anyway which lead to an additional
request. On the frontend, if the result set was empty, it kept retrying
until at least one result was returned. This bug is fixed in this commit
too.

app/assets/javascripts/discourse/app/controllers/user-activity-bookmarks.js

@@ -96,6 +96,7 @@ export default Controller.extend({
 
   _processLoadResponse(searchTerm, response) {
     if (!response || !response.user_bookmark_list) {
+      this.model.loadMoreUrl = null;
       return;
     }
 

app/models/user_bookmark_list.rb

@@ -5,7 +5,7 @@ class UserBookmarkList
 
   PER_PAGE = 20
 
-  attr_reader :bookmarks, :per_page
+  attr_reader :bookmarks, :per_page, :has_more
   attr_accessor :more_bookmarks_url, :bookmark_serializer_opts
 
   def initialize(user:, guardian:, params:)
@@ -21,7 +21,9 @@ class UserBookmarkList
   end
 
   def load(&blk)
-    @bookmarks = BookmarkQuery.new(user: @user, guardian: @guardian, params: @params).list_all(&blk)
+    query = BookmarkQuery.new(user: @user, guardian: @guardian, params: @params)
+    @bookmarks = query.list_all(&blk)
+    @has_more = (@params[:page].to_i + 1) * @params[:per_page] < query.count
     @bookmarks
   end
 

app/serializers/user_bookmark_list_serializer.rb

@@ -15,6 +15,6 @@ class UserBookmarkListSerializer < ApplicationSerializer
   end
 
   def include_more_bookmarks_url?
-    @include_more_bookmarks_url ||= object.bookmarks.size == object.per_page
+    @include_more_bookmarks_url ||= object.has_more
   end
 end

lib/bookmark_query.rb

@@ -26,7 +26,7 @@ class BookmarkQuery
     end
   end
 
-  attr_reader :guardian
+  attr_reader :guardian, :count
 
   def initialize(user:, guardian: nil, params: {})
     @user = user
@@ -34,6 +34,7 @@ class BookmarkQuery
     @guardian = guardian || Guardian.new(@user)
     @page = @params[:page].to_i
     @limit = @params[:limit].present? ? @params[:limit].to_i : @params[:per_page]
+    @count = 0
   end
 
   def list_all(&blk)
@@ -73,6 +74,8 @@ class BookmarkQuery
         bookmarks.updated_at DESC"
     )
 
+    @count = results.count
+
     if @page.positive?
       results = results.offset(@page * @params[:per_page])
     end

spec/models/user_bookmark_list_spec.rb

@@ -20,6 +20,7 @@ RSpec.describe UserBookmarkList do
   it "returns all types of bookmarks" do
     list.load
     expect(list.bookmarks.map(&:id)).to match_array([post_bookmark.id, topic_bookmark.id, user_bookmark.id])
+    expect(list.has_more).to eq(false)
   end
 
   it "defaults to 20 per page" do