metadata: Record installation options

Adds a new class called `Tab` that acts as a recipt for install options. A
`Tab` can be serialized to a JSON file for future reference.

Library/Homebrew/formula_installer.rb

@@ -2,6 +2,7 @@ require 'exceptions'
 require 'formula'
 require 'keg'
 require 'set'
+require 'tab'
 
 class FormulaInstaller
   attr :f
@@ -128,6 +129,9 @@ class FormulaInstaller
       data = read.read
       raise Marshal.load(data) unless data.nil? or data.empty?
       raise "Suspicious installation failure" unless $?.success?
+
+      # Write an installation receipt (a Tab) to the prefix
+      Tab.for_install(f, args).write
     end
   end
 

Library/Homebrew/tab.rb

@@ -0,0 +1,33 @@
+require 'ostruct'
+
+require 'formula'
+require 'vendor/multi_json'
+
+# Inherit from OpenStruct to gain a generic initialization method that takes a
+# hash and creates an attribute for each key and value. `Tab.new` probably
+# should not be called directly, instead use one of the class methods like
+# `Tab.for_install`.
+class Tab < OpenStruct
+  def self.for_install f, args
+    # Retrieve option flags from command line.
+    arg_options = args.options_only
+    # Pick off the option flags from the formula's `options` array by
+    # discarding the descriptions.
+    formula_options = f.options.map { |o, _| o }
+
+    Tab.new :used_options => formula_options & arg_options,
+            :unused_options => formula_options - arg_options,
+            :tabfile => f.prefix + 'INSTALL_RECEIPT.json'
+  end
+
+  def to_json
+    MultiJson.encode({
+      :used_options => used_options,
+      :unused_options => unused_options
+    })
+  end
+
+  def write
+    tabfile.write to_json
+  end
+end

bin/brew

@@ -5,6 +5,7 @@ HOMEBREW_BREW_FILE = ENV['HOMEBREW_BREW_FILE'] = File.expand_path(__FILE__)
 
 require 'pathname'
 HOMEBREW_LIBRARY_PATH = Pathname.new(__FILE__).realpath.dirname.parent.join("Library/Homebrew").to_s
+$:.unshift(HOMEBREW_LIBRARY_PATH + '/vendor')
 $:.unshift(HOMEBREW_LIBRARY_PATH)
 require 'global'