Properly identify task lists inside a blockquote

Updated the task list regex to understand blockquote
characters that can come before the task item marker

app/models/concerns/taskable.rb

@@ -15,7 +15,8 @@ module Taskable
   INCOMPLETE_PATTERN = /(\[[\s]\])/.freeze
   ITEM_PATTERN       = %r{
     ^
-    \s*(?:[-+*]|(?:\d+\.)) # list prefix required - task item has to be always in a list
+    (?:(?:>\s{0,4})*)         # optional blockquote characters
+    \s*(?:[-+*]|(?:\d+\.))    # list prefix required - task item has to be always in a list
     \s+                       # whitespace prefix has to be always presented for a list item
     (\[\s\]|\[[xX]\])         # checkbox
     (\s.+)                    # followed by whitespace and some text.

changelogs/unreleased/64697-markdown-issues-checkbox-inside-blockquote-status-won-t-be-saved.yml

+---
+title: Better support clickable tasklists inside blockquotes
+merge_request: 30952
+author:
+type: fixed

spec/services/task_list_toggle_service_spec.rb

@@ -114,6 +114,23 @@ describe TaskListToggleService do
     expect(toggler.execute).to be_falsey
   end
 
+  it 'properly handles tasks in a blockquote' do
+    markdown =
+      <<-EOT.strip_heredoc
+      > > * [ ] Task 1
+      > * [x] Task 2
+    EOT
+
+    markdown_html = Banzai::Pipeline::FullPipeline.call(markdown, project: nil)[:output].to_html
+    toggler = described_class.new(markdown, markdown_html,
+                                  toggle_as_checked: true,
+                                  line_source: '> > * [ ] Task 1', line_number: 1)
+
+    expect(toggler.execute).to be_truthy
+    expect(toggler.updated_markdown.lines[0]).to eq "> > * [x] Task 1\n"
+    expect(toggler.updated_markdown_html).to include('disabled checked> Task 1')
+  end
+
   it 'properly handles a GitLab blockquote' do
     markdown =
       <<-EOT.strip_heredoc

spec/support/shared_examples/taskable_shared_examples.rb

@@ -105,4 +105,25 @@ shared_examples 'a Taskable' do
       expect(subject.task_status_short).to match('1 task')
     end
   end
+
+  describe 'with tasks in blockquotes' do
+    before do
+      subject.description = <<-EOT.strip_heredoc
+        > - [ ] Task a
+        > > - [x] Task a.1
+
+        >>>
+        1. [ ] Task 1
+        1. [x] Task 2
+        >>>
+      EOT
+    end
+
+    it 'returns the correct task status' do
+      expect(subject.task_status).to match('2 of')
+      expect(subject.task_status).to match('4 tasks completed')
+      expect(subject.task_status_short).to match('2/')
+      expect(subject.task_status_short).to match('4 tasks')
+    end
+  end
 end