6 files changed, 53 insertions, 3 deletions
diff --git a/Library/Homebrew/build_environment.rb b/Library/Homebrew/build_environment.rb
index 18876f954..60e099977 100644
--- a/Library/Homebrew/build_environment.rb
+++ b/Library/Homebrew/build_environment.rb
@@ -18,9 +18,9 @@ class BuildEnvironment
     @settings.include? :userpaths
   end
 
-  def modify_build_environment
+  def modify_build_environment(context=nil)
     p = @settings.find { |s| Proc === s }
-    ENV.instance_eval(&p) unless p.nil?
+    ENV.instance_exec(context, &p) unless p.nil?
   end
 
   def _dump(*)
diff --git a/Library/Homebrew/dependencies.rb b/Library/Homebrew/dependencies.rb
index c2dd63d7d..54de50f39 100644
--- a/Library/Homebrew/dependencies.rb
+++ b/Library/Homebrew/dependencies.rb
@@ -190,7 +190,7 @@ class Requirement
   # Overriding modify_build_environment is deprecated, pass a block to
   # the env DSL method instead.
   def modify_build_environment
-    env.modify_build_environment
+    env.modify_build_environment(self)
   end
 
   def env
diff --git a/Library/Homebrew/extend/object.rb b/Library/Homebrew/extend/object.rb
new file mode 100644
index 000000000..8ffe5dc90
--- /dev/null
+++ b/Library/Homebrew/extend/object.rb
@@ -0,0 +1,15 @@
+class Object
+  def instance_exec(*args, &block)
+    method_name = :__temp_instance_exec_method
+    singleton_class = (class << self; self; end)
+    singleton_class.class_eval do
+      define_method(method_name, &block)
+    end
+
+    send(method_name, *args)
+  ensure
+    singleton_class.class_eval do
+      remove_method(method_name) if method_defined?(method_name)
+    end
+  end unless method_defined?(:instance_exec)
+end
diff --git a/Library/Homebrew/global.rb b/Library/Homebrew/global.rb
index 6440506f8..50d30e877 100644
--- a/Library/Homebrew/global.rb
+++ b/Library/Homebrew/global.rb
@@ -3,6 +3,7 @@ require 'extend/pathname'
 require 'extend/ARGV'
 require 'extend/string'
 require 'extend/symbol'
+require 'extend/object'
 require 'utils'
 require 'exceptions'
 require 'set'
diff --git a/Library/Homebrew/test/test_build_environment.rb b/Library/Homebrew/test/test_build_environment.rb
index d8a227f51..6710662b5 100644
--- a/Library/Homebrew/test/test_build_environment.rb
+++ b/Library/Homebrew/test/test_build_environment.rb
@@ -31,6 +31,20 @@ class BuildEnvironmentTests < Test::Unit::TestCase
     dump = Marshal.dump(@env)
     assert Marshal.load(dump).userpaths?
   end
+
+  def test_env_block
+    foo = mock("foo")
+    @env << Proc.new { foo.some_message }
+    foo.expects(:some_message)
+    @env.modify_build_environment
+  end
+
+  def test_env_block_with_argument
+    foo = mock("foo")
+    @env << Proc.new { |x| x.some_message }
+    foo.expects(:some_message)
+    @env.modify_build_environment(foo)
+  end
 end
 
 class BuildEnvironmentDSLTests < Test::Unit::TestCase
diff --git a/Library/Homebrew/test/test_object.rb b/Library/Homebrew/test/test_object.rb
new file mode 100644
index 000000000..debdd6c42
--- /dev/null
+++ b/Library/Homebrew/test/test_object.rb
@@ -0,0 +1,20 @@
+require 'testing_env'
+require 'extend/object'
+
+class InstanceExecTests < Test::Unit::TestCase
+  def test_evaluates_in_context_of_receiver
+    assert_equal 1, [1].instance_exec { first }
+  end
+
+  def test_passes_arguments_to_block
+    assert_equal 2, [1].instance_exec(1) { |x| first + x }
+  end
+
+  def test_does_not_persist_temporary_singleton_method
+    obj = Object.new
+    before = obj.methods
+    obj.instance_exec { methods }
+    after = obj.methods
+    assert_equal before, after
+  end
+end