1 files changed, 74 insertions, 0 deletions
diff --git a/Library/Homebrew/dependency.rb b/Library/Homebrew/dependency.rb
new file mode 100644
index 000000000..91b939c4f
--- /dev/null
+++ b/Library/Homebrew/dependency.rb
@@ -0,0 +1,74 @@
+require 'dependable'
+
+# A dependency on another Homebrew formula.
+class Dependency
+  include Dependable
+
+  attr_reader :name, :tags
+
+  def initialize(name, *tags)
+    @name = name
+    @tags = tags.flatten.compact
+  end
+
+  def to_s
+    name
+  end
+
+  def ==(other)
+    name == other.name
+  end
+
+  def eql?(other)
+    other.is_a?(self.class) && hash == other.hash
+  end
+
+  def hash
+    name.hash
+  end
+
+  def to_formula
+    f = Formula.factory(name)
+    # Add this dependency's options to the formula's build args
+    f.build.args = f.build.args.concat(options)
+    f
+  end
+
+  def installed?
+    to_formula.installed?
+  end
+
+  def requested?
+    ARGV.formulae.include?(to_formula) rescue false
+  end
+
+  def universal!
+    tags << 'universal' if to_formula.build.has_option? 'universal'
+  end
+
+  # Expand the dependencies of f recursively, optionally yielding
+  # [f, dep] to allow callers to apply arbitrary filters to the list.
+  # The default filter, which is used when a block is not supplied,
+  # omits optionals and recommendeds based on what the dependent has
+  # asked for.
+  def self.expand(dependent, &block)
+    dependent.deps.map do |dep|
+      prune = catch(:prune) do
+        if block_given?
+          yield dependent, dep
+        elsif dep.optional? || dep.recommended?
+          Dependency.prune unless dependent.build.with?(dep.name)
+        end
+      end
+
+      next if prune
+
+      expand(dep.to_formula, &block) << dep
+    end.flatten.compact.uniq
+  end
+
+  # Used to prune dependencies when calling expand_dependencies with a block.
+  def self.prune
+    throw(:prune, true)
+  end
+end