Implemented SimpleBuilder and updated Environment#add_builder method to support it

spec/build_tests_spec.rb

@@ -249,6 +249,27 @@ describe Rscons do
     ]
   end
 
+  it 'supports simple builders' do
+    test_dir('json_to_yaml')
+    Rscons::Environment.new do |env|
+      require 'json'
+      require 'yaml'
+      env.add_builder(:JsonToYaml) do |target, sources, cache, env, vars|
+        unless cache.up_to_date?(target, :JsonToYaml, sources, env)
+          cache.mkdir_p(File.dirname(target))
+          File.open(target, 'w') do |f|
+            f.write(YAML.dump(JSON.load(IO.read(sources.first))))
+          end
+          cache.register_build(target, :JsonToYaml, sources, env)
+        end
+        target
+      end
+      env.JsonToYaml('foo.yml','foo.json')
+    end
+    expect(File.exists?('foo.yml')).to be_truthy
+    expect(IO.read('foo.yml')).to eq("---\nkey: value\n")
+  end
+
   it 'cleans built files' do
     test_dir('build_dir')
     Rscons::Environment.new do |env|

spec/rscons/builders/simple_builder_spec.rb

@@ -0,0 +1,19 @@
+module Rscons
+  module Builders
+    describe SimpleBuilder do
+      let(:env) {Environment.new}
+
+      it "should create a new builder with the given name (as a symbol) and action" do
+        builder = Rscons::Builders::SimpleBuilder.new(:Foo) { 0x1234 }
+        expect(builder.name).to eq("Foo")
+        expect(builder.run(1,2,3,4,5)).to eq(0x1234)
+      end
+
+      it "should create a new builder with the given name (as a string) and action" do
+        builder = Rscons::Builders::SimpleBuilder.new("Foo") { 0x1234 }
+        expect(builder.name).to eq("Foo")
+        expect(builder.run(1,2,3,4,5)).to eq(0x1234)
+      end
+    end
+  end
+end

spec/rscons/environment_spec.rb

@@ -72,6 +72,13 @@ module Rscons
         env.add_builder(Rscons::Builders::Object.new)
         expect(env.builders.keys).to eq ["Object"]
       end
+
+      it "adds a new simple builder to the list of builders" do
+        env = Environment.new(exclude_builders: true)
+        expect(env.builders.keys).to eq []
+        env.add_builder(:Foo) {}
+        expect(env.builders.keys).to eq ["Foo"]
+      end
     end
 
     describe "#get_build_fname" do