discourse/lib/discourse_js_processor.rb

# frozen_string_literal: true
require "execjs"
require "mini_racer"

class DiscourseJsProcessor
  class TranspileError < StandardError
  end

  # To generate a list of babel plugins used by ember-cli, set
  # babel: { debug: true } in ember-cli-build.js, then run `yarn ember build -prod`
  DISCOURSE_COMMON_BABEL_PLUGINS = [
    ["proposal-decorators", { legacy: true }],
    "proposal-class-properties",
    "proposal-private-methods",
    "proposal-class-static-block",
    "transform-parameters",
    "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(%r{^/}, "")
    data = input[:data]

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

    # add sourceURL until we can do proper source maps
    if !Rails.env.production? && !ember_cli?(input[:filename])
      plugin_name = root_path[%r{/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, theme_id: nil)
    transpiler = Transpiler.new(skip_module: skip_module?(data))
    transpiler.perform(data, root_path, logical_path, theme_id: theme_id)
  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(%r{^/*}, "")

    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/")

    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
    end

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

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

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

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

    def self.mutex
      @mutex
    end

    def self.load_file_in_context(ctx, path, wrap_in_module: nil)
      contents = File.read("#{Rails.root}/app/assets/javascripts/#{path}")
      contents = <<~JS if wrap_in_module
          define(#{wrap_in_module.to_json}, ["exports", "require", "module"], function(exports, require, module){
            #{contents}
          });
        JS
      ctx.eval(contents, filename: path)
    end

    def self.create_new_context
      # timeout any eval that takes longer than 15 seconds
      ctx = MiniRacer::Context.new(timeout: 15_000, ensure_gc_after_idle: 2000)

      # General shims
      ctx.attach("rails.logger.info", proc { |err| Rails.logger.info(err.to_s) })
      ctx.attach("rails.logger.warn", proc { |err| Rails.logger.warn(err.to_s) })
      ctx.attach("rails.logger.error", proc { |err| Rails.logger.error(err.to_s) })
      ctx.eval(<<~JS, filename: "environment-setup.js")
        window = {};
        console = {
          prefix: "[DiscourseJsProcessor] ",
          log: function(...args){ rails.logger.info(console.prefix + args.join(" ")); },
          warn: function(...args){ rails.logger.warn(console.prefix + args.join(" ")); },
          error: function(...args){ rails.logger.error(console.prefix + args.join(" ")); }
        };
      JS

      # define/require support
      load_file_in_context(ctx, "node_modules/loader.js/dist/loader/loader.js")

      # Babel
      load_file_in_context(ctx, "node_modules/@babel/standalone/babel.js")
      ctx.eval <<~JS
        globalThis.rawBabelTransform = function(){
          return Babel.transform(...arguments).code;
        }
      JS

      # Terser
      load_file_in_context(ctx, "node_modules/source-map/dist/source-map.js")
      load_file_in_context(ctx, "node_modules/terser/dist/bundle.min.js")

      # Template Compiler
      load_file_in_context(ctx, "node_modules/ember-source/dist/ember-template-compiler.js")
      load_file_in_context(
        ctx,
        "node_modules/babel-plugin-ember-template-compilation/src/plugin.js",
        wrap_in_module: "babel-plugin-ember-template-compilation/index",
      )
      load_file_in_context(
        ctx,
        "node_modules/babel-plugin-ember-template-compilation/src/expression-parser.js",
        wrap_in_module: "babel-plugin-ember-template-compilation/expression-parser",
      )
      load_file_in_context(
        ctx,
        "node_modules/babel-import-util/src/index.js",
        wrap_in_module: "babel-import-util",
      )
      load_file_in_context(
        ctx,
        "node_modules/ember-cli-htmlbars/lib/colocated-babel-plugin.js",
        wrap_in_module: "colocated-babel-plugin",
      )

      # Widget HBS compiler
      widget_hbs_compiler_source = File.read("#{Rails.root}/lib/javascripts/widget-hbs-compiler.js")
      widget_hbs_compiler_source = <<~JS
        define("widget-hbs-compiler", ["exports"], function(exports){
          #{widget_hbs_compiler_source}
        });
      JS
      widget_hbs_compiler_transpiled =
        ctx.call(
          "rawBabelTransform",
          widget_hbs_compiler_source,
          { ast: false, moduleId: "widget-hbs-compiler", plugins: DISCOURSE_COMMON_BABEL_PLUGINS },
        )
      ctx.eval(widget_hbs_compiler_transpiled, filename: "widget-hbs-compiler.js")

      # Raw HBS compiler
      load_file_in_context(
        ctx,
        "node_modules/handlebars/dist/handlebars.js",
        wrap_in_module: "handlebars",
      )

      raw_hbs_transpiled =
        ctx.call(
          "rawBabelTransform",
          File.read(
            "#{Rails.root}/app/assets/javascripts/discourse-common/addon/lib/raw-handlebars.js",
          ),
          {
            ast: false,
            moduleId: "raw-handlebars",
            plugins: [
              ["transform-modules-amd", { noInterop: true }],
              *DISCOURSE_COMMON_BABEL_PLUGINS,
            ],
          },
        )
      ctx.eval(raw_hbs_transpiled, filename: "raw-handlebars.js")

      # Theme template AST transformation plugins
      load_file_in_context(
        ctx,
        "discourse-js-processor.js",
        wrap_in_module: "discourse-js-processor",
      )

      # Make interfaces available via `v8.call`
      ctx.eval <<~JS
        globalThis.compileRawTemplate = require('discourse-js-processor').compileRawTemplate;
        globalThis.transpile = require('discourse-js-processor').transpile;
        globalThis.minify = require('discourse-js-processor').minify;
        globalThis.getMinifyResult = require('discourse-js-processor').getMinifyResult;
      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

    # Call a method in the global scope of the v8 context.
    # The `fetch_result_call` kwarg provides a workaround for the lack of mini_racer async
    # result support. The first call can perform some async operation, and then `fetch_result_call`
    # will be called to fetch the result.
    def self.v8_call(*args, **kwargs)
      fetch_result_call = kwargs.delete(:fetch_result_call)
      mutex.synchronize do
        result = v8.call(*args, **kwargs)
        result = v8.call(fetch_result_call) if fetch_result_call
        result
      end
    rescue MiniRacer::RuntimeError => e
      message = e.message
      begin
        # Workaround for https://github.com/rubyjs/mini_racer/issues/262
        possible_encoded_message = message.delete_prefix("Error: ")
        decoded = JSON.parse("{\"value\": #{possible_encoded_message}}")["value"]
        message = "Error: #{decoded}"
      rescue JSON::ParserError
        message = e.message
      end
      transpile_error = TranspileError.new(message)
      transpile_error.set_backtrace(e.backtrace)
      raise transpile_error
    end

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

    def perform(source, root_path = nil, logical_path = nil, theme_id: nil)
      self.class.v8_call(
        "transpile",
        source,
        {
          skip_module: @skip_module,
          moduleId: module_name(root_path, logical_path),
          filename: logical_path || "unknown",
          themeId: theme_id,
          commonPlugins: DISCOURSE_COMMON_BABEL_PLUGINS,
        },
      )
    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 =~ %r{(.*/#{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(%r{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

    def compile_raw_template(source, theme_id: nil)
      self.class.v8_call("compileRawTemplate", source, theme_id)
    end

    def terser(tree, opts)
      self.class.v8_call("minify", tree, opts, fetch_result_call: "getMinifyResult")
    end
  end
end