Add type accessors to Dependencies

Library/Homebrew/dependable.rb

@@ -15,6 +15,10 @@ module Dependable
     tags.include? :recommended
   end
 
+  def required?
+    !build? && !optional? && !recommended?
+  end
+
   def options
     Options.coerce(tags - RESERVED_TAGS)
   end

Library/Homebrew/dependencies.rb

@@ -26,4 +26,24 @@ class Dependencies
     @deps
   end
   alias_method :to_ary, :to_a
+
+  def optional
+    select(&:optional?)
+  end
+
+  def recommended
+    select(&:recommended?)
+  end
+
+  def build
+    select(&:build?)
+  end
+
+  def required
+    select(&:required?)
+  end
+
+  def default
+    build + required + recommended
+  end
 end

Library/Homebrew/test/test_dependencies.rb

@@ -45,4 +45,18 @@ class DependenciesTests < Test::Unit::TestCase
     @deps << dep
     assert_equal [dep], @deps.to_ary
   end
+
+  def test_type_helpers
+    foo = Dependency.new("foo")
+    bar = Dependency.new("bar", [:optional])
+    baz = Dependency.new("baz", [:build])
+    qux = Dependency.new("qux", [:recommended])
+    quux = Dependency.new("quux")
+    @deps << foo << bar << baz << qux << quux
+    assert_equal [foo, quux], @deps.required
+    assert_equal [bar], @deps.optional
+    assert_equal [baz], @deps.build
+    assert_equal [qux], @deps.recommended
+    assert_equal [foo, baz, quux, qux].sort_by(&:name), @deps.default.sort_by(&:name)
+  end
 end