TODO see issue X is also a great way to link the two together.

Is the issue still worth fixing? Well the file was completely rewritten 1 year ago, the TODO removed, and no one requesting this now/pushing for it? Close it.

Have an issue but not sure if it's relevant so it stays open forever? I've seen issues outlive the code their for by decades because investigating the lots priority issue wasn't a priority, quick "see: function" references are similar, easily searchable terms which makes old issue review very fast to close. This also ensures the backlog is reviewed periodically