cleanup: remove broken symlink for uninstalled migrated Casks

Signed-off-by: Michael Cho <michael@michaelcho.dev>

Library/Homebrew/cleanup.rb

@@ -634,6 +634,20 @@ module Homebrew
         end
       end
 
+      require "cask/caskroom"
+      if Cask::Caskroom.path.directory?
+        Cask::Caskroom.path.each_child do |path|
+          path.extend(ObserverPathnameExtension)
+          next if !path.symlink? || path.resolved_path_exists?
+
+          if dry_run?
+            puts "Would remove (broken link): #{path}"
+          else
+            path.unlink
+          end
+        end
+      end
+
       return if dry_run?
 
       return if ObserverPathnameExtension.total.zero?

Library/Homebrew/test/cleanup_spec.rb

@@ -163,6 +163,20 @@ RSpec.describe Homebrew::Cleanup do
         expect(grandchild_dir).to exist
       end
     end
+
+    it "removes broken symlinks for uninstalled migrated Casks" do
+      caskroom = Cask::Caskroom.path
+      old_cask_dir = caskroom/"old"
+      new_cask_dir = caskroom/"new"
+      unrelated_cask_dir = caskroom/"other"
+      unrelated_cask_dir.mkpath
+      FileUtils.ln_s new_cask_dir, old_cask_dir
+
+      cleanup.prune_prefix_symlinks_and_directories
+      expect(unrelated_cask_dir).to exist
+      expect(old_cask_dir).not_to be_a_symlink
+      expect(old_cask_dir).not_to exist
+    end
   end
 
   specify "::cleanup_formula" do