4 files changed, 85 insertions, 6 deletions
diff --git a/Library/Homebrew/dependencies.rb b/Library/Homebrew/dependencies.rb
index 5d5b5ab0d..7c2ff7d1b 100644
--- a/Library/Homebrew/dependencies.rb
+++ b/Library/Homebrew/dependencies.rb
@@ -21,7 +21,7 @@ class DependencyCollector
 
   def initialize
     @deps = Dependencies.new
-    @requirements = Set.new
+    @requirements = ComparableSet.new
   end
 
   def add spec
@@ -196,6 +196,9 @@ end
 # This requirement is used to require an X11 implementation,
 # optionally with a minimum version number.
 class X11Dependency < Requirement
+  include Comparable
+  attr_reader :min_version
+
   def initialize min_version=nil
     @min_version = min_version
   end
@@ -217,9 +220,20 @@ class X11Dependency < Requirement
     ENV.x11
   end
 
-  def hash
-    "X11".hash
+  def <=> other
+    unless other.is_a? X11Dependency
+      raise TypeError, "expected X11Dependency"
+    end
+
+    if other.min_version.nil?
+      1
+    elsif @min_version.nil?
+      -1
+    else
+      @min_version <=> other.min_version
+    end
   end
+
 end
 
 
diff --git a/Library/Homebrew/extend/set.rb b/Library/Homebrew/extend/set.rb
new file mode 100644
index 000000000..b45b85de9
--- /dev/null
+++ b/Library/Homebrew/extend/set.rb
@@ -0,0 +1,24 @@
+require 'set'
+
+class ComparableSet < Set
+  def add new
+    # smileys only
+    return super new unless new.respond_to? :>
+
+    objs = find_all { |o| o.class == new.class }
+    objs.each do |o|
+      return self if o > new
+      delete o
+    end
+    super new
+  end
+
+  alias_method :<<, :add
+
+  # Set#merge bypasses enumerating the set's contents,
+  # so the subclassed #add would never be called
+  def merge enum
+    enum.is_a?(Enumerable) or raise ArgumentError, "value must be enumerable"
+    enum.each { |o| add(o) }
+  end
+end
diff --git a/Library/Homebrew/formula.rb b/Library/Homebrew/formula.rb
index d23aeea71..8f63cd705 100644
--- a/Library/Homebrew/formula.rb
+++ b/Library/Homebrew/formula.rb
@@ -6,6 +6,7 @@ require 'bottles'
 require 'patches'
 require 'compilers'
 require 'build_environment'
+require 'extend/set'
 
 
 class Formula
@@ -455,9 +456,9 @@ class Formula
   end
 
   def recursive_requirements
-    reqs = recursive_deps.map { |dep| dep.requirements }.to_set
-    reqs << requirements
-    reqs.flatten
+    reqs = ComparableSet.new
+    recursive_deps.each { |dep| reqs.merge dep.requirements }
+    reqs.merge requirements
   end
 
   def to_hash
diff --git a/Library/Homebrew/test/test_comparableset.rb b/Library/Homebrew/test/test_comparableset.rb
new file mode 100644
index 000000000..d39ad51d6
--- /dev/null
+++ b/Library/Homebrew/test/test_comparableset.rb
@@ -0,0 +1,40 @@
+require 'testing_env'
+require 'extend/set'
+
+class ComparableSetTests < Test::Unit::TestCase
+  def setup
+    @set = ComparableSet.new
+  end
+
+  def test_merging_multiple_dependencies
+    @set << X11Dependency.new
+    @set << X11Dependency.new
+    assert_equal @set.count, 1
+    @set << Requirement.new
+    assert_equal @set.count, 2
+  end
+
+  def test_comparison_prefers_larger
+    @set << X11Dependency.new
+    @set << X11Dependency.new('2.6')
+    assert_equal @set.count, 1
+    assert_equal @set.to_a, [X11Dependency.new('2.6')]
+  end
+
+  def test_comparison_does_not_merge_smaller
+    @set << X11Dependency.new('2.6')
+    @set << X11Dependency.new
+    assert_equal @set.count, 1
+    assert_equal @set.to_a, [X11Dependency.new('2.6')]
+  end
+
+  def test_merging_sets
+    @set << X11Dependency.new
+    @set << Requirement.new
+    reqs = Set.new [X11Dependency.new('2.6'), Requirement.new]
+    @set.merge reqs
+
+    assert_equal @set.count, 2
+    assert_equal @set.find {|r| r.is_a? X11Dependency}, X11Dependency.new('2.6')
+  end
+end