cleanup: remove broken symlink for uninstalled migrated Casks

[cho-m]

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Draft to rebase after #16871

Currently, if there is a cask_rename and user does brew migrate <cask> then brew uninstall <cask>, we leave behind a broken symlink in the Caskroom.

As far as I can tell, this requires a manual deletion. --prune=all / --prune-prefix doesn't handle Caskroom.

Not sure if possible to handle during brew uninstall so just went with adding additional symlink check in brew cleanup. I didn't do any empty directory removal and only left logic as direct symlinks inside Caskroom.

[cho-m]

Actually looks like logic may exist but it doesn't seem to work for me:

brew/Library/Homebrew/cask/installer.rb

Lines 562 to 566 in 857838a

	# Remove symlinks for renamed casks if they are now broken.
	@cask.old_tokens.each do |old_token|
	old_caskroom_path = Caskroom.path/old_token
	FileUtils.rm old_caskroom_path if old_caskroom_path.symlink? && !old_caskroom_path.exist?
	end

EDIT: It might be due to loading the Cask file that was used for installation. Loading Cask from tap has renames.

[MikeMcQuaid]

It might be due to loading the Cask file that was used for installation.

This seems likely.

IMO we should refactor the way this cask file storing/loading works so instead of storing the cask file sometimes and JSON other times: we store the minimum viable amount of JSON needed for e.g. uninstalling the cask.

[MikeMcQuaid]

Good catch, thanks @cho-m!