Implemented SimpleBuilder and updated Environment#add_builder method to support it

README.md

@@ -154,6 +154,31 @@ Rscons::Environment.new do |env|
 end
 ```
 
+### Example: Custom Builder Using Environment#add_builder()
+
+The `add_builder` method of the `Rscons::Environment` class optionally allows
+you to define and register a builder by providing a name and action block. This
+can be useful if the builder you are trying to define is easily expressed as a
+short ruby procedure. When `add_builder` is called in this manner a new builder
+will be registered with the environment with the given name. When this builder
+is used it will call the provided block in order to build the target.
+
+```ruby
+Rscons::Environment.new do |env|
+  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
+```
+
 ### Example: Using different compilation flags for some sources
 
 ```ruby

build_tests/json_to_yaml/foo.json

@@ -0,0 +1 @@
+{ "key": "value" }

lib/rscons.rb

@@ -13,6 +13,7 @@ require_relative "rscons/builders/library"
 require_relative "rscons/builders/object"
 require_relative "rscons/builders/preprocess"
 require_relative "rscons/builders/program"
+require_relative "rscons/builders/simple_builder"
 
 # Namespace module for rscons classes
 module Rscons

lib/rscons/builders/simple_builder.rb

@@ -0,0 +1,37 @@
+module Rscons
+  module Builders
+    # A Generic builder class whose name and operation is defined at
+    # instantiation.
+    class SimpleBuilder < Builder
+      # The name of this builder when registered in an environment
+      attr_reader :name
+
+      # Create a new builder with the given name and action.
+      #
+      # @param name  [String,Symbol] The name of the builder when registered.
+      # @param block [Block]
+      #   The action to perform when the builder is processed. The provided
+      #   block must return the target file on success or false on failure.
+      #   The provided block should have the same signature as {Builder#run}.
+      def initialize(name, &block)
+        @name  = name.to_s
+        @block = block
+      end
+
+      # Run the builder to produce a build target.
+      #
+      # @param target [String] Target file name.
+      # @param sources [Array<String>] Source file name(s).
+      # @param cache [Cache] The Cache object.
+      # @param env [Environment] The Environment executing the builder.
+      # @param vars [Hash,VarSet] Extra construction variables.
+      #
+      # @return [String,false]
+      #   Name of the target file on success or false on failure.
+      def run(target, sources, cache, env, vars)
+        @block.call(target, sources, cache, env, vars)
+      end
+    end
+  end
+end
+

lib/rscons/environment.rb

@@ -120,10 +120,26 @@ module Rscons
 
     # Add a {Builder} object to the Environment.
     #
-    # @param builder [Builder] The {Builder} object to add.
+    # @overload add_builder(builder)
+    #   Registers a builder with the environment
+    #   @param builder [Builder] An instance of the builder to register.
+    #
+    # @overload add_builder(builder,&action)
+    #   Register a new {Builders::SimpleBuilder} with the environment.
+    #
+    #   @param builder [String,Symbol]
+    #     The name of the builder to add.
+    #
+    #   @param action [Block]
+    #     A block that will be called when the builder is executed to generate
+    #     a target file. The provided block should have the same prototype as
+    #     {Rscons::Builder#run}
     #
     # @return [void]
-    def add_builder(builder)
+    def add_builder(builder, &action)
+      if not builder.is_a? Rscons::Builder
+        builder = Rscons::Builders::SimpleBuilder.new(builder, &action)
+      end
       @builders[builder.name] = builder
       var_defs = builder.default_variables(self)
       if var_defs

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