Object#instance_exec for Ruby 1.8.6

Not thread safe! But I don't think we care.

We want to evaluate the env DSL block in the context of ENV for asthetic
reasons, but we also want access to methods on the requirement instance.
We can use #instance_exec to pass the requirement itself into the block:

  class Foo < Requirement
    env do |req|
      append 'PATH', req.some_path
    end

    def some_path
      which 'something'
    end
  end

Also add a simplified version of Object#instance_exec for Ruby 1.8.6.

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(*)

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

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

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'

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

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