move CoreFormulaRepository into separate file

For users whose local brew is at around 2015-06-11 to 2015-08-06,
running `brew update` will emit following error:

  Error: uninitialized constant Formulary::CoreFormulaRepository

This is caused by the same bug described in Homebrew/homebrew#42553.

This commit workarounds this issue and restores `brew update` compatibility
for users mentioned above.

Also cleanup legacy `require "cmd/tap"`.

Library/Homebrew/cmd/install.rb

 require "blacklist"
 require "cmd/doctor"
 require "cmd/search"
-require "cmd/tap"
 require "formula_installer"
+require "tap"
+require "core_formula_repository"
 require "hardware"
 
 module Homebrew

Library/Homebrew/cmd/pull.rb

@@ -3,7 +3,8 @@
 
 require "utils"
 require "formula"
-require "cmd/tap"
+require "tap"
+require "core_formula_repository"
 
 module Homebrew
   def pull_url(url)

Library/Homebrew/cmd/readall.rb

@@ -4,7 +4,8 @@
 # or to determine if any current formulae have Ruby issues
 
 require "formula"
-require "cmd/tap"
+require "tap"
+require "core_formula_repository"
 require "thread"
 
 module Homebrew

Library/Homebrew/cmd/tap.rb

 require "tap"
+require "core_formula_repository"
 
 module Homebrew
   def tap

Library/Homebrew/cmd/test-bot.rb

@@ -29,7 +29,8 @@ require "date"
 require "rexml/document"
 require "rexml/xmldecl"
 require "rexml/cdata"
-require "cmd/tap"
+require "tap"
+require "core_formula_repository"
 
 module Homebrew
   BYTES_IN_1_MEGABYTE = 1024*1024

Library/Homebrew/core_formula_repository.rb

+require "tap"
+
+# A specialized {Tap} class to mimic the core formula file system, which shares many
+# similarities with normal {Tap}.
+# TODO Separate core formulae with core codes. See discussion below for future plan:
+#      https://github.com/Homebrew/homebrew/pull/46735#discussion_r46820565
+class CoreFormulaRepository < Tap
+  # @private
+  def initialize
+    @user = "Homebrew"
+    @repo = "homebrew"
+    @name = "Homebrew/homebrew"
+    @path = HOMEBREW_REPOSITORY
+  end
+
+  def self.instance
+    @instance ||= CoreFormulaRepository.new
+  end
+
+  # @private
+  def uninstall
+    raise "Tap#uninstall is not available for CoreFormulaRepository"
+  end
+
+  # @private
+  def pin
+    raise "Tap#pin is not available for CoreFormulaRepository"
+  end
+
+  # @private
+  def unpin
+    raise "Tap#unpin is not available for CoreFormulaRepository"
+  end
+
+  # @private
+  def pinned?
+    false
+  end
+
+  # @private
+  def command_files
+    []
+  end
+
+  # @private
+  def custom_remote?
+    remote != "https://github.com/#{user}/#{repo}.git"
+  end
+
+  # @private
+  def core_formula_repository?
+    true
+  end
+
+  # @private
+  def formula_dir
+    HOMEBREW_LIBRARY/"Formula"
+  end
+
+  # @private
+  def alias_dir
+    HOMEBREW_LIBRARY/"Aliases"
+  end
+
+  # @private
+  def formula_renames
+    require "formula_renames"
+    FORMULA_RENAMES
+  end
+
+  private
+
+  def formula_file_to_name(file)
+    file.basename(".rb").to_s
+  end
+
+  def alias_file_to_name(file)
+    file.basename.to_s
+  end
+end

Library/Homebrew/formula.rb

@@ -10,6 +10,7 @@ require "software_spec"
 require "install_renamed"
 require "pkg_version"
 require "tap"
+require "core_formula_repository"
 require "formula_renames"
 require "keg"
 require "migrator"

Library/Homebrew/formulary.rb

 require "digest/md5"
 require "formula_renames"
 require "tap"
+require "core_formula_repository"
 
 # The Formulary is responsible for creating instances of Formula.
 # It is not meant to be used directy from formulae.

Library/Homebrew/tap.rb

-require "utils/json"
-require "descriptions"
-
 # a {Tap} is used to extend the formulae provided by Homebrew core.
 # Usually, it's synced with a remote git repository. And it's likely
 # a Github repository with the name of `user/homebrew-repo`. In such
@@ -32,6 +29,7 @@ class Tap
     repo = repo.strip_prefix "homebrew-"
 
     if user == "Homebrew" && repo == "homebrew"
+      require "core_formula_repository"
       return CoreFormulaRepository.instance
     end
 
@@ -119,6 +117,7 @@ class Tap
   # @option options [String]  :clone_targe If passed, it will be used as the clone remote.
   # @option options [Boolean] :full_clone If set as true, full clone will be used.
   def install(options = {})
+    require "descriptions"
     raise TapAlreadyTappedError, name if installed?
 
     # ensure git is installed
@@ -180,6 +179,7 @@ class Tap
 
   # uninstall this {Tap}.
   def uninstall
+    require "descriptions"
     raise TapUnavailableError, name unless installed?
 
     puts "Untapping #{name}... (#{path.abv})"
@@ -326,6 +326,8 @@ class Tap
 
   # Hash with tap formula renames
   def formula_renames
+    require "utils/json"
+
     @formula_renames ||= if (rename_file = path/"formula_renames.json").file?
       Utils::JSON.load(rename_file.read)
     else
@@ -363,82 +365,3 @@ class Tap
     "#{name}/#{file.basename}"
   end
 end
-
-# A specialized {Tap} class to mimic the core formula file system, which shares many
-# similarities with normal {Tap}.
-# TODO Separate core formulae with core codes. See discussion below for future plan:
-#      https://github.com/Homebrew/homebrew/pull/46735#discussion_r46820565
-class CoreFormulaRepository < Tap
-  # @private
-  def initialize
-    @user = "Homebrew"
-    @repo = "homebrew"
-    @name = "Homebrew/homebrew"
-    @path = HOMEBREW_REPOSITORY
-  end
-
-  def self.instance
-    @instance ||= CoreFormulaRepository.new
-  end
-
-  # @private
-  def uninstall
-    raise "Tap#uninstall is not available for CoreFormulaRepository"
-  end
-
-  # @private
-  def pin
-    raise "Tap#pin is not available for CoreFormulaRepository"
-  end
-
-  # @private
-  def unpin
-    raise "Tap#unpin is not available for CoreFormulaRepository"
-  end
-
-  # @private
-  def pinned?
-    false
-  end
-
-  # @private
-  def command_files
-    []
-  end
-
-  # @private
-  def custom_remote?
-    remote != "https://github.com/#{user}/#{repo}.git"
-  end
-
-  # @private
-  def core_formula_repository?
-    true
-  end
-
-  # @private
-  def formula_dir
-    HOMEBREW_LIBRARY/"Formula"
-  end
-
-  # @private
-  def alias_dir
-    HOMEBREW_LIBRARY/"Aliases"
-  end
-
-  # @private
-  def formula_renames
-    require "formula_renames"
-    FORMULA_RENAMES
-  end
-
-  private
-
-  def formula_file_to_name(file)
-    file.basename(".rb").to_s
-  end
-
-  def alias_file_to_name(file)
-    file.basename.to_s
-  end
-end