Use the sourcepos attribute for finding tasks

2 files changed, 13 insertions, 6 deletions

diff --git a/app/services/issuable_base_service.rb b/app/services/issuable_base_service.rb
index 5719a4778f0..2835d598311 100644
--- a/app/services/issuable_base_service.rb
+++ b/app/services/issuable_base_service.rb
@@ -262,16 +262,16 @@ class IssuableBaseService < BaseService
 
   # Handle the `update_task` event sent from UI.  Attempts to update a specific
   # line in the markdown and cached html, bypassing any unnecessary updates or checks.
-  def update_task_event(issue)
+  def update_task_event(issuable)
     update_task_params = params.delete(:update_task)
     return unless update_task_params
 
-    toggler = TaskListToggleService.new(issue.description, issue.description_html,
+    toggler = TaskListToggleService.new(issuable.description, issuable.description_html,
                                         line_source: update_task_params[:line_source],
                                         line_number: update_task_params[:line_number],
                                         currently_checked: !update_task_params[:checked],
                                         index: update_task_params[:index],
-                                        sourcepos: false)
+                                        sourcepos: !issuable.legacy_markdown?)
 
     if toggler.execute
       # by updating the description_html field at the same time,
@@ -282,9 +282,9 @@ class IssuableBaseService < BaseService
       # since we're updating a very specific line, we don't care whether
       # the `lock_version` sent from the FE is the same or not.  Just
       # make sure the data hasn't changed since we queried it
-      params[:lock_version]     = issue.lock_version
+      params[:lock_version]     = issuable.lock_version
 
-      update_task(issue)
+      update_task(issuable)
     else
       # if we make it here, the data is much newer than we thought it was - fail fast
       raise ActiveRecord::StaleObjectError
diff --git a/app/services/task_list_toggle_service.rb b/app/services/task_list_toggle_service.rb
index 1b0a5965235..3ba0faa5009 100644
--- a/app/services/task_list_toggle_service.rb
+++ b/app/services/task_list_toggle_service.rb
@@ -11,7 +11,7 @@
 class TaskListToggleService
   attr_reader :updated_markdown, :updated_markdown_html
 
-  def initialize(markdown, markdown_html, line_source:, line_number:, currently_checked:, index:, sourcepos: false)
+  def initialize(markdown, markdown_html, line_source:, line_number:, currently_checked:, index:, sourcepos: true)
     @markdown, @markdown_html  = markdown, markdown_html
     @line_source, @line_number = line_source, line_number
     @currently_checked         = currently_checked
@@ -62,6 +62,13 @@ class TaskListToggleService
     @updated_markdown_html = html.to_html
   end
 
+  # When using CommonMark, we should be able to use the embedded `sourcepos` attribute to
+  # target the exact line in the DOM.  For RedCarpet, we need to use the index of the checkbox
+  # that was checked and match it with what we think is the same checkbox.
+  # The reason `sourcepos` is slightly more reliable is the case where a line of text is
+  # changed from a regular line into a checkbox (or vice versa).  Then the checked index
+  # in the UI will be off from the list of checkboxes we've calculated locally.
+  # It's a rare circumstance, but since we can account for it, we do.
   def get_html_checkbox(html)
     if use_sourcepos
       html.css(".task-list-item[data-sourcepos^='#{line_number}:'] > input.task-list-item-checkbox").first