add Environment#clone() and a build test for it

build_tests/clone_env/build.rb

@@ -0,0 +1,11 @@
+debug = Rscons::Environment.new do |env|
+  env.build_dir('src', 'debug')
+  env['CFLAGS'] = '-O2'
+  env['CPPFLAGS'] = '-DSTRING="Debug Version"'
+  env.Program('program-debug', Dir['src/*.c'])
+end
+
+release = debug.clone('CPPFLAGS' => '-DSTRING="Release Version"') do |env|
+  env.build_dir('src', 'release')
+  env.Program('program-release', Dir['src/*.c'])
+end

build_tests/clone_env/src/program.c

@@ -0,0 +1,6 @@
+#include <stdio.h>
+
+int main(int argc, char *argv[])
+{
+    printf("Hello, %s\n", STRING);
+}

lib/rscons/environment.rb

@@ -36,6 +36,24 @@ module Rscons
       end
     end
 
+    def clone(variables = {})
+      env = Environment.new()
+      @builders.each do |builder_name, builder|
+        env.add_builder(builder)
+      end
+      @build_dirs.each do |src_dir, obj_dir|
+        env.build_dir(src_dir, obj_dir)
+      end
+      env.append(@varset)
+      env.append(variables)
+
+      if block_given?
+        yield env
+        env.process
+      end
+      env
+    end
+
     def add_builder(builder)
       @builders[builder.class.short_name] = builder
       var_defs = builder.default_variables(self)

spec/build_tests_spec.rb

@@ -126,4 +126,14 @@ describe Rscons do
     File.exists?('inc.h').should be_true
     `./program`.should == "The value is 5678\n"
   end
+
+  it 'allows cloning Environment objects' do
+    lines = test_dir('clone_env')
+    lines.should == [
+      %q{gcc -c -o debug/program.o -MMD -MF debug/program.mf '-DSTRING="Debug Version"' -O2 src/program.c},
+      %q{gcc -o program-debug debug/program.o},
+      %q{gcc -c -o release/program.o -MMD -MF release/program.mf '-DSTRING="Release Version"' -O2 src/program.c},
+      %q{gcc -o program-release release/program.o},
+    ]
+  end
 end