Stop mutating dependency specifications

Library/Homebrew/dependency_collector.rb

@@ -40,7 +40,7 @@ class DependencyCollector
 
   def build(spec)
     spec, tags = case spec
-                 when Hash then spec.shift
+                 when Hash then destructure_spec_hash(spec)
                  else spec
                  end
 
@@ -49,6 +49,10 @@ class DependencyCollector
 
   private
 
+  def destructure_spec_hash(spec)
+    spec.each { |o| return o }
+  end
+
   def parse_spec(spec, tags)
     case spec
     when String

Library/Homebrew/test/test_dependency_collector.rb

@@ -128,4 +128,11 @@ class DependencyCollectorTests < Test::Unit::TestCase
   def test_raises_typeerror_for_unknown_types
     assert_raises(TypeError) { @d.add(Object.new) }
   end
+
+  def test_does_not_mutate_dependency_spec
+    spec = { 'foo' => :optional }
+    copy = spec.dup
+    @d.add(spec)
+    assert_equal copy, spec
+  end
 end