Add compatibility layer to convert caskroom/* to homebrew/cask(-*).

Library/Homebrew/compat.rb

@@ -9,3 +9,4 @@ require "compat/extend/string"
 require "compat/gpg"
 require "compat/dependable"
 require "compat/os/mac"
+require "compat/tap"

Library/Homebrew/compat/tap.rb

@@ -0,0 +1,18 @@
+module CaskTapMigrationExtension
+  def parse_user_repo(*args)
+    user, repo = super
+
+    if user == "caskroom"
+      user = "Homebrew"
+      repo = "cask-#{repo}" unless repo == "cask"
+    end
+
+    [user, repo]
+  end
+end
+
+class Tap
+  class << self
+    prepend CaskTapMigrationExtension
+  end
+end

Library/Homebrew/tap.rb

@@ -12,7 +12,7 @@ class Tap
 
   TAP_DIRECTORY = HOMEBREW_LIBRARY/"Taps"
 
-  def self.fetch(*args)
+  def self.parse_user_repo(*args)
     case args.length
     when 1
       user, repo = args.first.split("/", 2)
@@ -29,6 +29,13 @@ class Tap
     user = user.capitalize if ["homebrew", "linuxbrew"].include? user
     repo = repo.strip_prefix "homebrew-"
 
+    [user, repo]
+  end
+  private_class_method :parse_user_repo
+
+  def self.fetch(*args)
+    user, repo = parse_user_repo(*args)
+
     if ["Homebrew", "Linuxbrew"].include?(user) && ["core", "homebrew"].include?(repo)
       return CoreTap.instance
     end