discourse/lib/discourse_js_processor.rb

# frozen_string_literal: true
require 'execjs'
require 'mini_racer'

class DiscourseJsProcessor

  DISCOURSE_COMMON_BABEL_PLUGINS = [
    'proposal-optional-chaining',
    ['proposal-decorators', { legacy: true } ],
    'transform-template-literals',
    'proposal-class-properties',
    'proposal-class-static-block',
    'proposal-private-property-in-object',
    'proposal-private-methods',
    'proposal-numeric-separator',
    'proposal-logical-assignment-operators',
    'proposal-nullish-coalescing-operator',
    'proposal-json-strings',
    'proposal-optional-catch-binding',
    'transform-parameters',
    'proposal-async-generator-functions',
    'proposal-object-rest-spread',
    'proposal-export-namespace-from',
  ]

  def self.plugin_transpile_paths
    @@plugin_transpile_paths ||= Set.new
  end

  def self.ember_cli?(filename)
    filename.include?("/app/assets/javascripts/discourse/dist/")
  end

  def self.call(input)
    root_path = input[:load_path] || ''
    logical_path = (input[:filename] || '').sub(root_path, '').gsub(/\.(js|es6).*$/, '').sub(/^\//, '')
    data = input[:data]

    if should_transpile?(input[:filename])
      data = transpile(data, root_path, logical_path)
    end

    # add sourceURL until we can do proper source maps
    if !Rails.env.production? && !ember_cli?(input[:filename])
      plugin_name = root_path[/\/plugins\/([\w-]+)\/assets/, 1]
      source_url = if plugin_name
        "plugins/#{plugin_name}/assets/javascripts/#{logical_path}"
      else
        logical_path
      end

      data = "eval(#{data.inspect} + \"\\n//# sourceURL=#{source_url}\");\n"
    end

    { data: data }
  end

  def self.transpile(data, root_path, logical_path)
    transpiler = Transpiler.new(skip_module: skip_module?(data))
    transpiler.perform(data, root_path, logical_path)
  end

  def self.should_transpile?(filename)
    filename ||= ''

    # skip ember cli
    return false if ember_cli?(filename)

    # es6 is always transpiled
    return true if filename.end_with?(".es6") || filename.end_with?(".es6.erb")

    # For .js check the path...
    return false unless filename.end_with?(".js") || filename.end_with?(".js.erb")

    relative_path = filename.sub(Rails.root.to_s, '').sub(/^\/*/, '')

    js_root = "app/assets/javascripts"
    test_root = "test/javascripts"

    return false if relative_path.start_with?("#{js_root}/locales/")
    return false if relative_path.start_with?("#{js_root}/plugins/")

    return true if %w(
      start-discourse
      onpopstate-handler
      google-tag-manager
      google-universal-analytics-v3
      google-universal-analytics-v4
      activate-account
      auto-redirect
      embed-application
      app-boot
    ).any? { |f| relative_path == "#{js_root}/#{f}.js" }

    return true if plugin_transpile_paths.any? { |prefix| relative_path.start_with?(prefix) }

    !!(relative_path =~ /^#{js_root}\/[^\/]+\// ||
      relative_path =~ /^#{test_root}\/[^\/]+\//)
  end

  def self.skip_module?(data)
    !!(data.present? && data =~ /^\/\/ discourse-skip-module$/)
  end

  class Transpiler
    @mutex = Mutex.new
    @ctx_init = Mutex.new

    def self.mutex
      @mutex
    end

    def self.create_new_context
      # timeout any eval that takes longer than 15 seconds
      ctx = MiniRacer::Context.new(timeout: 15000, ensure_gc_after_idle: 2000)
      ctx.eval("#{File.read("#{Rails.root}/app/assets/javascripts/node_modules/@babel/standalone/babel.js")}")
      ctx.eval(File.read(Ember::Source.bundled_path_for('ember-template-compiler.js')))
      ctx.eval("module = {}; exports = {};")
      ctx.eval("const DISCOURSE_COMMON_BABEL_PLUGINS = #{DISCOURSE_COMMON_BABEL_PLUGINS.to_json};")
      ctx.attach("rails.logger.info", proc { |err| Rails.logger.info(err.to_s) })
      ctx.attach("rails.logger.error", proc { |err| Rails.logger.error(err.to_s) })
      ctx.eval <<JS
      console = {
        prefix: "",
        log: function(msg){ rails.logger.info(console.prefix + msg); },
        error: function(msg){ rails.logger.error(console.prefix + msg); }
      }

JS
      source = File.read("#{Rails.root}/lib/javascripts/widget-hbs-compiler.js")
      js_source = ::JSON.generate(source, quirks_mode: true)
      js = ctx.eval("Babel.transform(#{js_source}, { ast: false, plugins: ['transform-arrow-functions', 'transform-block-scoped-functions', 'transform-block-scoping', 'transform-computed-properties', 'transform-destructuring', 'transform-duplicate-keys', 'transform-for-of', 'transform-function-name', 'transform-literals', 'transform-object-super', 'transform-parameters', 'transform-shorthand-properties', 'transform-spread', 'transform-sticky-regex', 'transform-template-literals', 'transform-typeof-symbol', 'transform-unicode-regex', 'proposal-object-rest-spread', 'proposal-optional-chaining'] }).code")
      ctx.eval(js)

      ctx
    end

    def self.reset_context
      @ctx&.dispose
      @ctx = nil
    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

    def initialize(skip_module: false)
      @skip_module = skip_module
    end

    def perform(source, root_path = nil, logical_path = nil)
      klass = self.class
      klass.mutex.synchronize do
        klass.v8.eval("console.prefix = 'BABEL: babel-eval: ';")
        transpiled = babel_source(
          source,
          module_name: module_name(root_path, logical_path),
          filename: logical_path
        )
        @output = klass.v8.eval(transpiled)
      end
    end

    def babel_source(source, opts = nil)
      opts ||= {}

      js_source = ::JSON.generate(source, quirks_mode: true)

      if opts[:module_name] && !@skip_module
        filename = opts[:filename] || 'unknown'
        <<~JS
          Babel.transform(
            #{js_source},
            {
              moduleId: '#{opts[:module_name]}',
              filename: '#{filename}',
              ast: false,
              plugins: [
                exports.WidgetHbsCompiler,
                ['transform-modules-amd', {noInterop: true}],
                ...DISCOURSE_COMMON_BABEL_PLUGINS
              ]
            }
          ).code
        JS
      else
        <<~JS
          Babel.transform(
            #{js_source},
            {
              ast: false,
              plugins: [
                exports.WidgetHbsCompiler,
                ...DISCOURSE_COMMON_BABEL_PLUGINS
              ]
            }
          ).code
        JS
      end
    end

    def module_name(root_path, logical_path)
      path = nil

      root_base = File.basename(Rails.root)
      # If the resource is a plugin, use the plugin name as a prefix
      if root_path =~ /(.*\/#{root_base}\/plugins\/[^\/]+)\//
        plugin_path = "#{Regexp.last_match[1]}/plugin.rb"

        plugin = Discourse.plugins.find { |p| p.path == plugin_path }
        path = "discourse/plugins/#{plugin.name}/#{logical_path.sub(/javascripts\//, '')}" if plugin
      end

      # We need to strip the app subdirectory to replicate how ember-cli works.
      path || logical_path&.gsub('app/', '')&.gsub('addon/', '')&.gsub('admin/addon', 'admin')
    end

  end
end