Transpile ES6 even without node, just using rubyracer

config/application.rb

@@ -32,6 +32,7 @@ module Discourse
     # -- all .rb files in that directory are automatically loaded.
 
     require 'discourse'
+    require 'es6_module_transpiler/rails'
     require 'js_locale_helper'
 
     # mocha hates us, active_support/testing/mochaing.rb line 2 is requiring the wrong

lib/es6_module_transpiler/rails.rb

@@ -0,0 +1,39 @@
+require 'es6_module_transpiler/rails/version'
+require 'es6_module_transpiler/tilt'
+require 'es6_module_transpiler/sprockets'
+
+module ES6ModuleTranspiler
+  def self.compile_to
+    @compile_to || :amd
+  end
+
+  def self.compile_to=(target)
+    @compile_to = target
+  end
+
+  def self.prefix_patterns
+    @prefix_patterns ||= []
+  end
+
+  def self.add_prefix_pattern(pattern, prefix)
+    prefix_patterns << [pattern, prefix]
+  end
+
+  def self.lookup_prefix(path)
+    _, prefix = prefix_patterns.detect {|pattern, prefix| pattern =~ path }
+
+    prefix
+  end
+
+  def self.transform=(transform)
+    @transform = transform
+  end
+
+  def self.transform
+    @transform
+  end
+
+  def self.compiler_options
+    @compiler_options ||= {}
+  end
+end

lib/es6_module_transpiler/rails/version.rb

@@ -0,0 +1,5 @@
+module ES6ModuleTranspiler
+  module Rails
+    VERSION = '0.4.0'
+  end
+end

lib/es6_module_transpiler/sprockets.rb

@@ -0,0 +1,3 @@
+require 'sprockets'
+
+Sprockets.register_engine '.es6', Tilt::ES6ModuleTranspilerTemplate

lib/es6_module_transpiler/support/es6_node_runner.js

@@ -0,0 +1,22 @@
+(function(program, execJS) { execJS(program) })(function(module, exports, console) {
+  #{source}
+}, function(program) {
+  var output, print = function(string) {
+    process.stdout.write('' + string);
+  };
+  try {
+    result = program();
+    if (typeof result == 'undefined' && result !== null) {
+      print('["ok"]');
+    } else {
+      try {
+        print(JSON.stringify(['ok', result]));
+      } catch (err) {
+        print('["err"]');
+      }
+    }
+  } catch (err) {
+    print(JSON.stringify(['err', '' + err]));
+  }
+});
+

lib/es6_module_transpiler/tilt.rb

@@ -0,0 +1,4 @@
+require 'tilt'
+require 'es6_module_transpiler/tilt/es6_module_transpiler_template'
+
+Tilt.register Tilt::ES6ModuleTranspilerTemplate, 'es6'

lib/es6_module_transpiler/tilt/es6_module_transpiler_template.rb

@@ -0,0 +1,109 @@
+require 'execjs'
+
+module Tilt
+  class ES6ModuleTranspilerTemplate < Tilt::Template
+    self.default_mime_type = 'application/javascript'
+
+    @mutex = Mutex.new
+    @ctx_init = Mutex.new
+
+    def prepare
+      # intentionally left empty
+      # Tilt requires this method to be defined
+    end
+
+    def self.create_new_context
+      ctx = V8::Context.new(timeout: 5000)
+      ctx.eval("module = {}; exports = {};");
+      ctx.load("#{Rails.root}/lib/es6_module_transpiler/support/es6-module-transpiler.js")
+      ctx
+    end
+
+    def self.v8
+      return @ctx if @ctx
+
+      # ensure we only init one of these
+      @ctx_init.synchronize do
+        return @ctx if @ctx
+        @ctx = create_new_context
+      end
+
+      @ctx
+    end
+
+    class JavaScriptError < StandardError
+      attr_accessor :message, :backtrace
+
+      def initialize(message, backtrace)
+        @message = message
+        @backtrace = backtrace
+      end
+
+    end
+
+    def self.protect
+      rval = nil
+      @mutex.synchronize do
+        begin
+          rval = yield
+          # This may seem a bit odd, but we don't want to leak out
+          # objects that require locks on the v8 vm, to get a backtrace
+          # you need a lock, if this happens in the wrong spot you can
+          # deadlock a process
+        rescue V8::Error => e
+          raise JavaScriptError.new(e.message, e.backtrace)
+        end
+      end
+      rval
+    end
+
+    def evaluate(scope, locals, &block)
+      return @output if @output
+
+      klass = self.class
+      klass.protect do
+        @output = klass.v8.eval(generate_source(scope))
+      end
+      @output
+    end
+
+    private
+
+    def transpiler_path
+      File.expand_path('../../support/es6-module-transpiler.js', __FILE__)
+    end
+
+    def generate_source(scope)
+      "new module.exports.Compiler(#{::JSON.generate(data, quirks_mode: true)}, '#{module_name(scope.root_path, scope.logical_path)}', #{compiler_options}).#{compiler_method}()"
+    end
+
+    def module_name(root_path, logical_path)
+      path = ''
+      if prefix = ES6ModuleTranspiler.lookup_prefix(File.join(root_path, logical_path))
+        path = File.join(prefix, logical_path)
+      else
+        path = logical_path
+      end
+
+      if ES6ModuleTranspiler.transform
+        path = ES6ModuleTranspiler.transform.call(path)
+      end
+
+      path
+    end
+
+    def compiler_method
+      type = {
+        amd: 'AMD',
+        cjs: 'CJS',
+        globals: 'Globals'
+      }[ES6ModuleTranspiler.compile_to.to_sym]
+
+      "to#{type}"
+    end
+
+    def compiler_options
+      ::JSON.generate(ES6ModuleTranspiler.compiler_options, quirks_mode: true)
+    end
+  end
+end