Fix #5153: Using the child metatag without an id causes unexpected behavior

app/models/post.rb

@@ -526,11 +526,15 @@ class Post < ApplicationRecord
           end
 
         in "-child", ids
+          next if ids.blank?
+
           children.search(id: ids).each do |post|
             post.update!(parent_id: nil)
           end
 
         in "child", ids
+          next if ids.blank?
+
           Post.search(id: ids).where.not(id: id).limit(10).each do |post|
             post.update!(parent_id: id)
           end

test/unit/post_test.rb

@@ -798,27 +798,55 @@ class PostTest < ActiveSupport::TestCase
         end
 
         context "for a child" do
-          should "add and remove children" do
+          should "add children with child:ids" do
-            @children = FactoryBot.create_list(:post, 3, parent_id: nil)
+            @children = create_list(:post, 3, parent: nil)
-
             @post.update(tag_string: "aaa child:#{@children.first.id}..#{@children.last.id}")
+
             assert_equal(true, @post.reload.has_children?)
             assert_equal(@post.id, @children[0].reload.parent_id)
             assert_equal(@post.id, @children[1].reload.parent_id)
             assert_equal(@post.id, @children[2].reload.parent_id)
+          end
 
+          should "remove children with -child:ids" do
+            @children = create_list(:post, 3, parent: @post)
             @post.update(tag_string: "aaa -child:#{@children.first.id}")
+
             assert_equal(true, @post.reload.has_children?)
             assert_nil(@children[0].reload.parent_id)
             assert_equal(@post.id, @children[1].reload.parent_id)
             assert_equal(@post.id, @children[2].reload.parent_id)
+          end
+
+          should "remove all children with child:none" do
+            @children = create_list(:post, 3, parent: @post)
+            @post.update!(tag_string: "aaa child:none")
 
-            @post.update(tag_string: "aaa child:none")
             assert_equal(false, @post.reload.has_children?)
             assert_nil(@children[0].reload.parent_id)
             assert_nil(@children[1].reload.parent_id)
             assert_nil(@children[2].reload.parent_id)
           end
+
+          should "not add children with child:" do
+            @children = create_list(:post, 3, parent: nil)
+            @post.update(tag_string: "aaa child:")
+
+            assert_equal(false, @post.reload.has_children?)
+            assert_nil(@children[0].reload.parent_id)
+            assert_nil(@children[1].reload.parent_id)
+            assert_nil(@children[2].reload.parent_id)
+          end
+
+          should "not remove children with -child:" do
+            @children = create_list(:post, 3, parent: @post)
+            @post.update!(tag_string: "aaa -child:")
+
+            assert_equal(true, @post.reload.has_children?)
+            assert_equal(@post, @children[0].reload.parent)
+            assert_equal(@post, @children[1].reload.parent)
+            assert_equal(@post, @children[2].reload.parent)
+          end
         end
 
         context "for status:active" do