Merge pull request #2825 from reitermarkus/refactoring

Refactoring using `Forwardable` and `DelegateClass`.

30 files changed, 207 insertions, 289 deletions

diff --git a/Library/Homebrew/cask/lib/hbc/artifact/base.rb b/Library/Homebrew/cask/lib/hbc/artifact/base.rb
index 2d9330b13..ae15552a4 100644
--- a/Library/Homebrew/cask/lib/hbc/artifact/base.rb
+++ b/Library/Homebrew/cask/lib/hbc/artifact/base.rb
@@ -1,6 +1,8 @@
 module Hbc
   module Artifact
     class Base
+      extend Predicable
+
       def self.artifact_name
         @artifact_name ||= name.sub(/^.*:/, "").gsub(/(.)([A-Z])/, '\1_\2').downcase
       end
@@ -65,13 +67,7 @@ module Hbc
         {}
       end
 
-      def verbose?
-        @verbose
-      end
-
-      def force?
-        @force
-      end
+      attr_predicate :force?, :verbose?
 
       def initialize(cask, command: SystemCommand, force: false, verbose: false)
         @cask = cask
diff --git a/Library/Homebrew/cask/lib/hbc/cask.rb b/Library/Homebrew/cask/lib/hbc/cask.rb
index e1cdb5dea..672d18954 100644
--- a/Library/Homebrew/cask/lib/hbc/cask.rb
+++ b/Library/Homebrew/cask/lib/hbc/cask.rb
@@ -1,5 +1,3 @@
-require "forwardable"
-
 require "hbc/dsl"
 require "hbc/metadata"
 
@@ -73,6 +71,15 @@ module Hbc
       @token
     end
 
+    def hash
+      token.hash
+    end
+
+    def eql?(other)
+      token == other.token
+    end
+    alias == eql?
+
     def dumpcask
       odebug "Cask instance dumps in YAML:"
       odebug "Cask instance toplevel:", to_yaml
diff --git a/Library/Homebrew/cask/lib/hbc/cask_dependencies.rb b/Library/Homebrew/cask/lib/hbc/cask_dependencies.rb
index 8bba5df8e..0edda074e 100644
--- a/Library/Homebrew/cask/lib/hbc/cask_dependencies.rb
+++ b/Library/Homebrew/cask/lib/hbc/cask_dependencies.rb
@@ -1,35 +1,36 @@
+require "delegate"
+
 require "hbc/topological_hash"
 
 module Hbc
-  class CaskDependencies
-    attr_reader :cask, :graph, :sorted
+  class CaskDependencies < DelegateClass(Array)
+    attr_reader :cask, :graph
 
     def initialize(cask)
       @cask = cask
       @graph = graph_dependencies
-      @sorted = sort
+      super(sort)
     end
 
-    def graph_dependencies
-      deps_in = ->(csk) { csk.depends_on ? csk.depends_on.cask || [] : [] }
-      walk = lambda do |acc, deps|
-        deps.each do |dep|
-          next if acc.key?(dep)
-          succs = deps_in.call CaskLoader.load(dep)
-          acc[dep] = succs
-          walk.call(acc, succs)
-        end
-        acc
-      end
+    private
 
-      graphed = walk.call({}, @cask.depends_on.cask)
-      TopologicalHash[graphed]
+    def graph_dependencies(cask = self.cask, acc = TopologicalHash.new)
+      return acc if acc.key?(cask)
+      deps = cask.depends_on.cask.map(&CaskLoader.public_method(:load))
+      acc[cask] = deps
+      deps.each do |dep|
+        graph_dependencies(dep, acc)
+      end
+      acc
     end
 
     def sort
-      @graph.tsort
+      raise CaskSelfReferencingDependencyError, cask.token if graph[cask].include?(cask)
+      graph.tsort - [cask]
     rescue TSort::Cyclic
-      raise CaskCyclicCaskDependencyError, @cask.token
+      strongly_connected_components = graph.strongly_connected_components.sort_by(&:count)
+      cyclic_dependencies = strongly_connected_components.last - [cask]
+      raise CaskCyclicDependencyError.new(cask.token, cyclic_dependencies.join(", "))
     end
   end
 end
diff --git a/Library/Homebrew/cask/lib/hbc/cask_loader.rb b/Library/Homebrew/cask/lib/hbc/cask_loader.rb
index 43fd9080d..8cd010ef6 100644
--- a/Library/Homebrew/cask/lib/hbc/cask_loader.rb
+++ b/Library/Homebrew/cask/lib/hbc/cask_loader.rb
@@ -1,12 +1,14 @@
 module Hbc
   module CaskLoader
     class FromContentLoader
+      attr_reader :content
+
       def initialize(content)
         @content = content
       end
 
       def load
-        instance_eval(@content.force_encoding("UTF-8"), __FILE__, __LINE__)
+        instance_eval(content.force_encoding("UTF-8"), __FILE__, __LINE__)
       end
 
       private
@@ -18,25 +20,25 @@ module Hbc
 
     class FromPathLoader < FromContentLoader
       def self.can_load?(ref)
-        path = Pathname.new(ref)
+        path = Pathname(ref)
         path.extname == ".rb" && path.expand_path.exist?
       end
 
       attr_reader :token, :path
 
       def initialize(path)
-        path = Pathname.new(path).expand_path
+        path = Pathname(path).expand_path
 
         @token = path.basename(".rb").to_s
         @path = path
       end
 
       def load
-        raise CaskUnavailableError.new(@token, "'#{@path}' does not exist.")  unless @path.exist?
-        raise CaskUnavailableError.new(@token, "'#{@path}' is not readable.") unless @path.readable?
-        raise CaskUnavailableError.new(@token, "'#{@path}' is not a file.")   unless @path.file?
+        raise CaskUnavailableError.new(token, "'#{path}' does not exist.")  unless path.exist?
+        raise CaskUnavailableError.new(token, "'#{path}' is not readable.") unless path.readable?
+        raise CaskUnavailableError.new(token, "'#{path}' is not a file.")   unless path.file?
 
-        @content = IO.read(@path)
+        @content = IO.read(path)
 
         super
       end
@@ -44,11 +46,11 @@ module Hbc
       private
 
       def cask(header_token, &block)
-        if @token != header_token
-          raise CaskTokenMismatchError.new(@token, header_token)
+        if token != header_token
+          raise CaskTokenMismatchError.new(token, header_token)
         end
 
-        Cask.new(header_token, sourcefile_path: @path, &block)
+        Cask.new(header_token, sourcefile_path: path, &block)
       end
     end
 
@@ -65,14 +67,13 @@ module Hbc
       end
 
       def load
-        Hbc.cache.mkpath
-        FileUtils.rm_f @path
+        path.dirname.mkpath
 
         begin
-          ohai "Downloading #{@url}."
-          curl @url, "-o", @path
+          ohai "Downloading #{url}."
+          curl url, "-o", path
         rescue ErrorDuringExecution
-          raise CaskUnavailableError.new(@token, "Failed to download #{Formatter.url(@url)}.")
+          raise CaskUnavailableError.new(token, "Failed to download #{Formatter.url(url)}.")
         end
 
         super
@@ -84,15 +85,17 @@ module Hbc
         ref.to_s.match?(HOMEBREW_TAP_CASK_REGEX)
       end
 
+      attr_reader :tap
+
       def initialize(tapped_name)
-        user, repo, token = tapped_name.split("/", 3).map(&:downcase)
+        user, repo, token = tapped_name.split("/", 3)
         @tap = Tap.fetch(user, repo)
 
         super @tap.cask_dir/"#{token}.rb"
       end
 
       def load
-        @tap.install unless @tap.installed?
+        tap.install unless tap.installed?
 
         super
       end
@@ -104,12 +107,12 @@ module Hbc
       end
 
       def initialize(ref)
-        @token = File.basename(ref, ".rb")
-        super CaskLoader.default_path(@token)
+        token = File.basename(ref, ".rb")
+        super CaskLoader.default_path(token)
       end
 
       def load
-        raise CaskUnavailableError.new(@token, "No Cask with this name exists.")
+        raise CaskUnavailableError.new(token, "No Cask with this name exists.")
       end
     end
 
diff --git a/Library/Homebrew/cask/lib/hbc/checkable.rb b/Library/Homebrew/cask/lib/hbc/checkable.rb
index 03f052629..604dd3f89 100644
--- a/Library/Homebrew/cask/lib/hbc/checkable.rb
+++ b/Library/Homebrew/cask/lib/hbc/checkable.rb
@@ -1,29 +1,27 @@
 module Hbc
   module Checkable
     def errors
-      Array(@errors)
+      @errors ||= []
     end
 
     def warnings
-      Array(@warnings)
+      @warnings ||= []
     end
 
     def add_error(message)
-      @errors ||= []
-      @errors << message
+      errors << message
     end
 
     def add_warning(message)
-      @warnings ||= []
-      @warnings << message
+      warnings << message
     end
 
     def errors?
-      Array(@errors).any?
+      errors.any?
     end
 
     def warnings?
-      Array(@warnings).any?
+      warnings.any?
     end
 
     def result
diff --git a/Library/Homebrew/cask/lib/hbc/download_strategy.rb b/Library/Homebrew/cask/lib/hbc/download_strategy.rb
index 5b32b4840..28ae704ee 100644
--- a/Library/Homebrew/cask/lib/hbc/download_strategy.rb
+++ b/Library/Homebrew/cask/lib/hbc/download_strategy.rb
@@ -100,7 +100,7 @@ module Hbc
     end
 
     def _fetch
-      odebug "Calling curl with args #{cask_curl_args.utf8_inspect}"
+      odebug "Calling curl with args #{cask_curl_args}"
       curl(*cask_curl_args)
     end
 
diff --git a/Library/Homebrew/cask/lib/hbc/dsl.rb b/Library/Homebrew/cask/lib/hbc/dsl.rb
index 92245e8fb..112ceb943 100644
--- a/Library/Homebrew/cask/lib/hbc/dsl.rb
+++ b/Library/Homebrew/cask/lib/hbc/dsl.rb
@@ -211,10 +211,10 @@ module Hbc
 
     # depends_on uses a load method so that multiple stanzas can be merged
     def depends_on(*args)
-      return @depends_on if args.empty?
       @depends_on ||= DSL::DependsOn.new
+      return @depends_on if args.empty?
       begin
-        @depends_on.load(*args) unless args.empty?
+        @depends_on.load(*args)
       rescue RuntimeError => e
         raise CaskInvalidError.new(token, e)
       end
diff --git a/Library/Homebrew/cask/lib/hbc/dsl/depends_on.rb b/Library/Homebrew/cask/lib/hbc/dsl/depends_on.rb
index a8c1a1b73..bdef4239a 100644
--- a/Library/Homebrew/cask/lib/hbc/dsl/depends_on.rb
+++ b/Library/Homebrew/cask/lib/hbc/dsl/depends_on.rb
@@ -24,6 +24,8 @@ module Hbc
 
       def initialize
         @pairs ||= {}
+        @cask ||= []
+        @formula ||= []
       end
 
       def load(pairs = {})
@@ -53,12 +55,10 @@ module Hbc
       end
 
       def formula=(*args)
-        @formula ||= []
         @formula.concat(args)
       end
 
       def cask=(*args)
-        @cask ||= []
         @cask.concat(args)
       end
 
diff --git a/Library/Homebrew/cask/lib/hbc/exceptions.rb b/Library/Homebrew/cask/lib/hbc/exceptions.rb
index d9e1b07db..1a246be65 100644
--- a/Library/Homebrew/cask/lib/hbc/exceptions.rb
+++ b/Library/Homebrew/cask/lib/hbc/exceptions.rb
@@ -77,9 +77,15 @@ module Hbc
     end
   end
 
-  class CaskCyclicCaskDependencyError < AbstractCaskErrorWithToken
+  class CaskCyclicDependencyError < AbstractCaskErrorWithToken
     def to_s
-      "Cask '#{token}' includes cyclic dependencies on other Casks and could not be installed."
+      "Cask '#{token}' includes cyclic dependencies on other Casks" << (reason.empty? ? "." : ": #{reason}")
+    end
+  end
+
+  class CaskSelfReferencingDependencyError < CaskCyclicDependencyError
+    def to_s
+      "Cask '#{token}' depends on itself."
     end
   end
 
@@ -91,7 +97,7 @@ module Hbc
 
   class CaskInvalidError < AbstractCaskErrorWithToken
     def to_s
-      "Cask '#{token}' definition is invalid" << (reason.empty? ? ".": ": #{reason}")
+      "Cask '#{token}' definition is invalid" << (reason.empty? ? "." : ": #{reason}")
     end
   end
 
diff --git a/Library/Homebrew/cask/lib/hbc/installer.rb b/Library/Homebrew/cask/lib/hbc/installer.rb
index aa6d600f7..252205a3b 100644
--- a/Library/Homebrew/cask/lib/hbc/installer.rb
+++ b/Library/Homebrew/cask/lib/hbc/installer.rb
@@ -1,11 +1,14 @@
 require "rubygems"
 
+require "formula_installer"
+
 require "hbc/cask_dependencies"
 require "hbc/staged"
 require "hbc/verify"
 
 module Hbc
   class Installer
+    extend Predicable
     # TODO: it is unwise for Hbc::Staged to be a module, when we are
     #       dealing with both staged and unstaged Casks here. This should
     #       either be a class which is only sometimes instantiated, or there
@@ -27,21 +30,7 @@ module Hbc
       @reinstall = false
     end
 
-    def skip_cask_deps?
-      @skip_cask_deps
-    end
-
-    def force?
-      @force
-    end
-
-    def binaries?
-      @binaries
-    end
-
-    def verbose?
-      @verbose
-    end
+    attr_predicate :binaries?, :force?, :skip_cask_deps?, :require_sha?, :verbose?
 
     def self.print_caveats(cask)
       odebug "Printing caveats"
@@ -75,7 +64,7 @@ module Hbc
       odebug "Hbc::Installer#fetch"
 
       satisfy_dependencies
-      verify_has_sha if @require_sha && !force?
+      verify_has_sha if require_sha? && !force?
       download
       verify
     end
@@ -210,7 +199,6 @@ module Hbc
       x11_dependencies
       formula_dependencies
       cask_dependencies unless skip_cask_deps?
-      puts "complete"
     end
 
     def macos_dependencies
@@ -247,36 +235,50 @@ module Hbc
     end
 
     def formula_dependencies
-      return unless @cask.depends_on.formula && !@cask.depends_on.formula.empty?
-      ohai "Installing Formula dependencies from Homebrew"
-      @cask.depends_on.formula.each do |dep_name|
-        print "#{dep_name} ... "
-        installed = @command.run(HOMEBREW_BREW_FILE,
-                                 args:         ["list", "--versions", dep_name],
-                                 print_stderr: false).stdout.include?(dep_name)
-        if installed
-          puts "already installed"
-        else
-          @command.run!(HOMEBREW_BREW_FILE,
-                        args: ["install", dep_name])
-          puts "done"
+      formulae = @cask.depends_on.formula.map { |f| Formula[f] }
+      return if formulae.empty?
+
+      if formulae.all?(&:any_version_installed?)
+        puts "All Formula dependencies satisfied."
+        return
+      end
+
+      not_installed = formulae.reject(&:any_version_installed?)
+
+      ohai "Installing Formula dependencies: #{not_installed.map(&:to_s).join(", ")}"
+      not_installed.each do |formula|
+        begin
+          old_argv = ARGV.dup
+          ARGV.replace([])
+          FormulaInstaller.new(formula).tap do |fi|
+            fi.installed_as_dependency = true
+            fi.installed_on_request = false
+            fi.show_header = true
+            fi.verbose = verbose?
+            fi.prelude
+            fi.install
+            fi.finish
+          end
+        ensure
+          ARGV.replace(old_argv)
         end
       end
     end
 
     def cask_dependencies
-      return unless @cask.depends_on.cask && !@cask.depends_on.cask.empty?
-      ohai "Installing Cask dependencies: #{@cask.depends_on.cask.join(", ")}"
-      deps = CaskDependencies.new(@cask)
-      deps.sorted.each do |dep_token|
-        puts "#{dep_token} ..."
-        dep = CaskLoader.load(dep_token)
-        if dep.installed?
-          puts "already installed"
-        else
-          Installer.new(dep, binaries: binaries?, verbose: verbose?, skip_cask_deps: true, force: false).install
-          puts "done"
-        end
+      return if @cask.depends_on.cask.empty?
+      casks = CaskDependencies.new(@cask)
+
+      if casks.all?(&:installed?)
+        puts "All Cask dependencies satisfied."
+        return
+      end
+
+      not_installed = casks.reject(&:installed?)
+
+      ohai "Installing Cask dependencies: #{not_installed.map(&:to_s).join(", ")}"
+      not_installed.each do |cask|
+        Installer.new(cask, binaries: binaries?, verbose: verbose?, skip_cask_deps: true, force: false).install
       end
     end
 
diff --git a/Library/Homebrew/cask/lib/hbc/system_command.rb b/Library/Homebrew/cask/lib/hbc/system_command.rb
index 6414a9e80..901617b71 100644
--- a/Library/Homebrew/cask/lib/hbc/system_command.rb
+++ b/Library/Homebrew/cask/lib/hbc/system_command.rb
@@ -20,7 +20,7 @@ module Hbc
 
     def run!
       @processed_output = { stdout: "", stderr: "" }
-      odebug "Executing: #{expanded_command.utf8_inspect}"
+      odebug "Executing: #{expanded_command}"
 
       each_output_line do |type, line|
         case type
@@ -62,7 +62,7 @@ module Hbc
 
     def assert_success
       return if processed_status && processed_status.success?
-      raise CaskCommandFailedError.new(command.utf8_inspect, processed_output[:stdout], processed_output[:stderr], processed_status)
+      raise CaskCommandFailedError.new(command, processed_output[:stdout], processed_output[:stderr], processed_status)
     end
 
     def expanded_command
@@ -162,7 +162,7 @@ module Hbc
           raise CaskError, <<-EOS
     Empty result parsing plist output from command.
       command was:
-      #{command.utf8_inspect}
+      #{command}
       output we attempted to parse:
       #{output}
           EOS
diff --git a/Library/Homebrew/cask/lib/hbc/url.rb b/Library/Homebrew/cask/lib/hbc/url.rb
index 07b41fb80..15da2ced2 100644
--- a/Library/Homebrew/cask/lib/hbc/url.rb
+++ b/Library/Homebrew/cask/lib/hbc/url.rb
@@ -1,5 +1,3 @@
-require "forwardable"
-
 module Hbc
   class URL
     FAKE_USER_AGENT = "Mozilla/5.0 (Macintosh; Intel Mac OS X 10) https://caskroom.github.io".freeze
diff --git a/Library/Homebrew/cask/lib/hbc/url_checker.rb b/Library/Homebrew/cask/lib/hbc/url_checker.rb
index 60a15ca2f..7076b13c5 100644
--- a/Library/Homebrew/cask/lib/hbc/url_checker.rb
+++ b/Library/Homebrew/cask/lib/hbc/url_checker.rb
@@ -38,7 +38,7 @@ module Hbc
     def _check_response_status
       ok = OK_RESPONSES[cask.url.scheme]
       return if ok.include?(@response_status)
-      add_error "unexpected http response, expecting #{ok.map(&:utf8_inspect).join(" or ")}, got #{@response_status.utf8_inspect}"
+      add_error "unexpected http response, expecting #{ok.map(&:to_s).join(" or ")}, got #{@response_status}"
     end
 
     def _get_data_from_request
diff --git a/Library/Homebrew/cask/lib/hbc/utils.rb b/Library/Homebrew/cask/lib/hbc/utils.rb
index 59e85aaeb..22f826e74 100644
--- a/Library/Homebrew/cask/lib/hbc/utils.rb
+++ b/Library/Homebrew/cask/lib/hbc/utils.rb
@@ -4,24 +4,15 @@ require "stringio"
 
 BUG_REPORTS_URL = "https://github.com/caskroom/homebrew-cask#reporting-bugs".freeze
 
-# monkeypatch Object - not a great idea
-class Object
-  def utf8_inspect
-    return inspect unless defined?(Encoding)
-    return map(&:utf8_inspect) if respond_to?(:map)
-    inspect.force_encoding("UTF-8").sub(/\A"(.*)"\Z/, '\1')
-  end
-end
-
 class Buffer < StringIO
+  extend Predicable
+
+  attr_predicate :tty?
+
   def initialize(tty = false)
     super()
     @tty = tty
   end
-
-  def tty?
-    @tty
-  end
 end
 
 # global methods
diff --git a/Library/Homebrew/caveats.rb b/Library/Homebrew/caveats.rb
index ee09063fd..2d0ceeb48 100644
--- a/Library/Homebrew/caveats.rb
+++ b/Library/Homebrew/caveats.rb
@@ -1,4 +1,6 @@
 class Caveats
+  extend Forwardable
+
   attr_reader :f
 
   def initialize(f)
@@ -25,9 +27,7 @@ class Caveats
     caveats.compact.join("\n")
   end
 
-  def empty?
-    caveats.empty?
-  end
+  delegate [:empty?, :to_s] => :caveats
 
   private
 
diff --git a/Library/Homebrew/checksum.rb b/Library/Homebrew/checksum.rb
index 1b095ea32..506885fce 100644
--- a/Library/Homebrew/checksum.rb
+++ b/Library/Homebrew/checksum.rb
@@ -1,6 +1,7 @@
 class Checksum
+  extend Forwardable
+
   attr_reader :hash_type, :hexdigest
-  alias to_s hexdigest
 
   TYPES = [:sha256].freeze
 
@@ -9,9 +10,7 @@ class Checksum
     @hexdigest = hexdigest
   end
 
-  def empty?
-    hexdigest.empty?
-  end
+  delegate [:empty?, :to_s] => :@hexdigest
 
   def ==(other)
     hash_type == other.hash_type && hexdigest == other.hexdigest
diff --git a/Library/Homebrew/cmd/info.rb b/Library/Homebrew/cmd/info.rb
index 98200a0b4..731156f95 100644
--- a/Library/Homebrew/cmd/info.rb
+++ b/Library/Homebrew/cmd/info.rb
@@ -169,8 +169,8 @@ module Homebrew
       Homebrew.dump_options_for_formula f
     end
 
-    c = Caveats.new(f)
-    ohai "Caveats", c.caveats unless c.empty?
+    caveats = Caveats.new(f)
+    ohai "Caveats", caveats.to_s unless caveats.empty?
   end
 
   def decorate_dependencies(dependencies)
diff --git a/Library/Homebrew/cmd/update-report.rb b/Library/Homebrew/cmd/update-report.rb
index aa1fd244d..374bbbd73 100644
--- a/Library/Homebrew/cmd/update-report.rb
+++ b/Library/Homebrew/cmd/update-report.rb
@@ -547,6 +547,8 @@ class Reporter
 end
 
 class ReporterHub
+  extend Forwardable
+
   attr_reader :reporters
 
   def initialize
@@ -564,9 +566,7 @@ class ReporterHub
     @hash.update(report) { |_key, oldval, newval| oldval.concat(newval) }
   end
 
-  def empty?
-    @hash.empty?
-  end
+  delegate :empty? => :@hash
 
   def dump
     # Key Legend: Added (A), Copied (C), Deleted (D), Modified (M), Renamed (R)
diff --git a/Library/Homebrew/debrew.rb b/Library/Homebrew/debrew.rb
index 7ff2c0360..c2662c9ee 100644
--- a/Library/Homebrew/debrew.rb
+++ b/Library/Homebrew/debrew.rb
@@ -74,18 +74,13 @@ module Debrew
     end
   end
 
-  class << self
-    alias original_raise raise
-  end
-
   @active = false
   @debugged_exceptions = Set.new
 
-  def self.active?
-    @active
-  end
-
   class << self
+    extend Predicable
+    alias original_raise raise
+    attr_predicate :active?
     attr_reader :debugged_exceptions
   end
 
diff --git a/Library/Homebrew/dependencies.rb b/Library/Homebrew/dependencies.rb
index 951db078d..0ed0502d8 100644
--- a/Library/Homebrew/dependencies.rb
+++ b/Library/Homebrew/dependencies.rb
@@ -1,28 +1,11 @@
-class Dependencies
-  include Enumerable
+require "delegate"
 
-  def initialize
-    @deps = []
+class Dependencies < DelegateClass(Array)
+  def initialize(*args)
+    super(args)
   end
 
-  def each(*args, &block)
-    @deps.each(*args, &block)
-  end
-
-  def <<(o)
-    @deps << o
-    self
-  end
-
-  def empty?
-    @deps.empty?
-  end
-
-  def *(arg)
-    @deps * arg
-  end
-
-  alias to_ary to_a
+  alias eql? ==
 
   def optional
     select(&:optional?)
@@ -44,40 +27,28 @@ class Dependencies
     build + required + recommended
   end
 
-  attr_reader :deps
-  protected :deps
-
-  def ==(other)
-    deps == other.deps
-  end
-  alias eql? ==
-
   def inspect
-    "#<#{self.class.name}: #{to_a.inspect}>"
+    "#<#{self.class.name}: #{to_a}>"
   end
 end
 
-class Requirements
-  include Enumerable
-
-  def initialize
-    @reqs = Set.new
-  end
-
-  def each(*args, &block)
-    @reqs.each(*args, &block)
+class Requirements < DelegateClass(Set)
+  def initialize(*args)
+    super(Set.new(args))
   end
 
   def <<(other)
     if other.is_a?(Comparable)
-      @reqs.grep(other.class) do |req|
+      grep(other.class) do |req|
         return self if req > other
-        @reqs.delete(req)
+        delete(req)
       end
     end
-    @reqs << other
+    super
     self
   end
 
-  alias to_ary to_a
+  def inspect
+    "#<#{self.class.name}: {#{to_a.join(", ")}}>"
+  end
 end
diff --git a/Library/Homebrew/dependency.rb b/Library/Homebrew/dependency.rb
index 4a452440a..d7d5ec59c 100644
--- a/Library/Homebrew/dependency.rb
+++ b/Library/Homebrew/dependency.rb
@@ -2,6 +2,7 @@ require "dependable"
 
 # A dependency on another Homebrew formula.
 class Dependency
+  extend Forwardable
   include Dependable
 
   attr_reader :name, :tags, :env_proc, :option_names
@@ -34,9 +35,7 @@ class Dependency
     formula
   end
 
-  def installed?
-    to_formula.installed?
-  end
+  delegate installed?: :to_formula
 
   def satisfied?(inherited_options)
     installed? && missing_options(inherited_options).empty?
diff --git a/Library/Homebrew/download_strategy.rb b/Library/Homebrew/download_strategy.rb
index 78f6c1e28..717334714 100644
--- a/Library/Homebrew/download_strategy.rb
+++ b/Library/Homebrew/download_strategy.rb
@@ -3,6 +3,7 @@ require "rexml/document"
 require "time"
 
 class AbstractDownloadStrategy
+  extend Forwardable
   include FileUtils
 
   attr_reader :meta, :name, :version, :resource
@@ -181,9 +182,7 @@ class VCSDownloadStrategy < AbstractDownloadStrategy
     @clone
   end
 
-  def head?
-    version.head?
-  end
+  delegate head?: :version
 
   # Return last commit's unique identifier for the repository.
   # Return most recent modified timestamp unless overridden.
diff --git a/Library/Homebrew/extend/predicable.rb b/Library/Homebrew/extend/predicable.rb
new file mode 100644
index 000000000..d02fbb89b
--- /dev/null
+++ b/Library/Homebrew/extend/predicable.rb
@@ -0,0 +1,9 @@
+module Predicable
+  def attr_predicate(*attrs)
+    attrs.each do |attr|
+      define_method attr do
+        instance_variable_get("@#{attr.to_s.sub(/\?$/, "")}") == true
+      end
+    end
+  end
+end
diff --git a/Library/Homebrew/formula.rb b/Library/Homebrew/formula.rb
index 66993a348..0d000496b 100644
--- a/Library/Homebrew/formula.rb
+++ b/Library/Homebrew/formula.rb
@@ -45,6 +45,7 @@ class Formula
   include Utils::Inreplace
   include Utils::Shell
   extend Enumerable
+  extend Forwardable
 
   # @!method inreplace(paths, before = nil, after = nil)
   # Actually implemented in {Utils::Inreplace.inreplace}.
@@ -314,37 +315,14 @@ class Formula
     active_spec == head
   end
 
-  # @private
-  def bottle_unneeded?
-    active_spec.bottle_unneeded?
-  end
-
-  # @private
-  def bottle_disabled?
-    active_spec.bottle_disabled?
-  end
-
-  # @private
-  def bottle_disable_reason
-    active_spec.bottle_disable_reason
-  end
-
-  # Does the currently active {SoftwareSpec} have any bottle?
-  # @private
-  def bottle_defined?
-    active_spec.bottle_defined?
-  end
-
-  # Does the currently active {SoftwareSpec} have an installable bottle?
-  # @private
-  def bottled?
-    active_spec.bottled?
-  end
-
-  # @private
-  def bottle_specification
-    active_spec.bottle_specification
-  end
+  delegate [
+    :bottle_unneeded?,
+    :bottle_disabled?,
+    :bottle_disable_reason,
+    :bottle_defined?,
+    :bottled?,
+    :bottle_specification,
+  ] => :active_spec
 
   # The Bottle object for the currently active {SoftwareSpec}.
   # @private
@@ -353,24 +331,21 @@ class Formula
   end
 
   # The description of the software.
+  # @method desc
   # @see .desc
-  def desc
-    self.class.desc
-  end
+  delegate desc: :"self.class"
 
   # The homepage for the software.
+  # @method homepage
   # @see .homepage
-  def homepage
-    self.class.homepage
-  end
+  delegate homepage: :"self.class"
 
   # The version for the currently active {SoftwareSpec}.
   # The version is autodetected from the URL and/or tag so only needs to be
   # declared if it cannot be autodetected correctly.
+  # @method version
   # @see .version
-  def version
-    active_spec.version
-  end
+  delegate version: :active_spec
 
   def update_head_version
     return unless head?
@@ -394,9 +369,8 @@ class Formula
   # Additional downloads can be defined as {#resource}s.
   # {Resource#stage} will create a temporary directory and yield to a block.
   # <pre>resource("additional_files").stage { bin.install "my/extra/tool" }</pre>
-  def resource(name)
-    active_spec.resource(name)
-  end
+  # @method resource
+  delegate resource: :active_spec
 
   # An old name for the formula
   def oldname
@@ -416,68 +390,39 @@ class Formula
   end
 
   # The {Resource}s for the currently active {SoftwareSpec}.
-  def resources
-    active_spec.resources.values
-  end
+  # @method resources
+  def_delegator :"active_spec.resources", :values, :resources
 
   # The {Dependency}s for the currently active {SoftwareSpec}.
-  # @private
-  def deps
-    active_spec.deps
-  end
+  delegate deps: :active_spec
 
   # The {Requirement}s for the currently active {SoftwareSpec}.
-  # @private
-  def requirements
-    active_spec.requirements
-  end
+  delegate requirements: :active_spec
 
   # The cached download for the currently active {SoftwareSpec}.
-  # @private
-  def cached_download
-    active_spec.cached_download
-  end
+  delegate cached_download: :active_spec
 
   # Deletes the download for the currently active {SoftwareSpec}.
-  # @private
-  def clear_cache
-    active_spec.clear_cache
-  end
+  delegate clear_cache: :active_spec
 
   # The list of patches for the currently active {SoftwareSpec}.
-  # @private
-  def patchlist
-    active_spec.patches
-  end
+  def_delegator :active_spec, :patches, :patchlist
 
   # The options for the currently active {SoftwareSpec}.
-  # @private
-  def options
-    active_spec.options
-  end
+  delegate options: :active_spec
 
   # The deprecated options for the currently active {SoftwareSpec}.
-  # @private
-  def deprecated_options
-    active_spec.deprecated_options
-  end
+  delegate deprecated_options: :active_spec
 
   # The deprecated option flags for the currently active {SoftwareSpec}.
-  # @private
-  def deprecated_flags
-    active_spec.deprecated_flags
-  end
+  delegate deprecated_flags: :active_spec
 
   # If a named option is defined for the currently active {SoftwareSpec}.
-  def option_defined?(name)
-    active_spec.option_defined?(name)
-  end
+  # @method option_defined?
+  delegate option_defined?: :active_spec
 
   # All the {.fails_with} for the currently active {SoftwareSpec}.
-  # @private
-  def compiler_failures
-    active_spec.compiler_failures
-  end
+  delegate compiler_failures: :active_spec
 
   # If this {Formula} is installed.
   # This is actually just a check for if the {#installed_prefix} directory
diff --git a/Library/Homebrew/formula_installer.rb b/Library/Homebrew/formula_installer.rb
index a365c967a..27786e77e 100644
--- a/Library/Homebrew/formula_installer.rb
+++ b/Library/Homebrew/formula_installer.rb
@@ -17,6 +17,7 @@ require "development_tools"
 
 class FormulaInstaller
   include FormulaCellarChecks
+  extend Predicable
 
   def self.mode_attr_accessor(*names)
     attr_accessor(*names)
@@ -559,11 +560,11 @@ class FormulaInstaller
 
     audit_installed if ARGV.homebrew_developer? && !formula.keg_only?
 
-    c = Caveats.new(formula)
+    caveats = Caveats.new(formula)
 
-    return if c.empty?
+    return if caveats.empty?
     @show_summary_heading = true
-    ohai "Caveats", c.caveats
+    ohai "Caveats", caveats.to_s
   end
 
   def finish
@@ -879,9 +880,7 @@ class FormulaInstaller
 
   private
 
-  def hold_locks?
-    @hold_locks || false
-  end
+  attr_predicate :hold_locks?
 
   def lock
     return unless (@@locked ||= []).empty?
diff --git a/Library/Homebrew/formula_support.rb b/Library/Homebrew/formula_support.rb
index 4d963a55e..a4534291a 100644
--- a/Library/Homebrew/formula_support.rb
+++ b/Library/Homebrew/formula_support.rb
@@ -81,7 +81,7 @@ class BottleDisableReason
   end
 
   def to_s
-    if @type == :unneeded
+    if unneeded?
       "This formula doesn't require compiling."
     else
       @reason
diff --git a/Library/Homebrew/global.rb b/Library/Homebrew/global.rb
index f36b01874..9f79781b4 100644
--- a/Library/Homebrew/global.rb
+++ b/Library/Homebrew/global.rb
@@ -1,4 +1,6 @@
+require "forwardable"
 require "extend/module"
+require "extend/predicable"
 require "extend/fileutils"
 require "extend/pathname"
 require "extend/git_repository"
diff --git a/Library/Homebrew/resource.rb b/Library/Homebrew/resource.rb
index c0e9dbada..1e55b69c5 100644
--- a/Library/Homebrew/resource.rb
+++ b/Library/Homebrew/resource.rb
@@ -1,7 +1,6 @@
 require "download_strategy"
 require "checksum"
 require "version"
-require "forwardable"
 
 # Resource is the fundamental representation of an external resource. The
 # primary formula download, along with other declared resources, are instances
diff --git a/Library/Homebrew/software_spec.rb b/Library/Homebrew/software_spec.rb
index eaae724a4..dd6cea8b2 100644
--- a/Library/Homebrew/software_spec.rb
+++ b/Library/Homebrew/software_spec.rb
@@ -1,4 +1,3 @@
-require "forwardable"
 require "resource"
 require "checksum"
 require "version"
diff --git a/Library/Homebrew/test/cask/depends_on_spec.rb b/Library/Homebrew/test/cask/depends_on_spec.rb
index 0299c243a..4b78820ce 100644
--- a/Library/Homebrew/test/cask/depends_on_spec.rb
+++ b/Library/Homebrew/test/cask/depends_on_spec.rb
@@ -12,7 +12,7 @@ describe "Satisfy Dependencies and Requirements", :cask do
   describe "depends_on cask" do
     context "when depends_on cask is cyclic" do
       let(:cask) { Hbc::CaskLoader.load_from_file(TEST_FIXTURE_DIR/"cask/Casks/with-depends-on-cask-cyclic.rb") }
-      it { is_expected.to raise_error(Hbc::CaskCyclicCaskDependencyError) }
+      it { is_expected.to raise_error(Hbc::CaskCyclicDependencyError) }
     end
 
     context do