Make `HOMEBREW_PREFIX/Caskroom` the default.

Library/Homebrew/cask/lib/hbc.rb

@@ -49,6 +49,7 @@ module Hbc
     Hbc::Cache.ensure_cache_exists
     Hbc::Cache.migrate_legacy_cache
 
+    Hbc::Caskroom.migrate_caskroom_from_repo_to_prefix
     Hbc::Caskroom.ensure_caskroom_exists
   end
 

Library/Homebrew/cask/lib/hbc/caskroom.rb

 module Hbc::Caskroom
   module_function
 
+  def migrate_caskroom_from_repo_to_prefix
+    repo_caskroom = Hbc.homebrew_repository.join("Caskroom")
+    if !Hbc.caskroom.exist? && repo_caskroom.directory?
+      ohai "Moving Caskroom from HOMEBREW_REPOSITORY to HOMEBREW_PREFIX"
+      FileUtils.mv repo_caskroom, Hbc.caskroom
+    end
+  end
+
   def ensure_caskroom_exists
     unless Hbc.caskroom.exist?
       ohai "Creating Caskroom at #{Hbc.caskroom}"

Library/Homebrew/cask/lib/hbc/cli/list.rb

@@ -79,4 +79,8 @@ class Hbc::CLI::List < Hbc::CLI::Base
   def self.help
     "with no args, lists installed Casks; given installed Casks, lists staged files"
   end
+
+  def self.needs_init?
+    true
+  end
 end

Library/Homebrew/cask/lib/hbc/locations.rb

@@ -9,7 +9,7 @@ module Hbc::Locations
     end
 
     def default_caskroom
-      @default_caskroom ||= homebrew_repository.join("Caskroom")
+      @default_caskroom ||= homebrew_prefix.join("Caskroom")
     end
 
     def caskroom