DEV: `@babel/plugin-proposal-decorators` -> `decorator-transforms` (#25290)

decorator-transforms (https://github.com/ef4/decorator-transforms) is a modern replacement for babel's plugin-proposal-decorators. It provides a decorator implementation using modern browser features, without needing to enable babel's full suite of class feature transformations. This improves the developer experience and performance.

In local testing with Google's 'tachometer' tool, this reduces Discourse's 'init-to-render' time by around 3-4% (230ms -> 222ms).

It reduces our initial gzip'd JS payloads by 3.2% (2.43MB -> 2.35MB), or 7.5% (14.5MB -> 13.4MB) uncompressed.

app/assets/javascripts/admin/index.js

@@ -6,6 +6,23 @@ const path = require("path");
 module.exports = {
   name: require("./package").name,
 
+  options: {
+    babel: {
+      plugins: [
+        [
+          require.resolve("decorator-transforms"),
+          {
+            runEarly: true,
+          },
+        ],
+      ],
+    },
+
+    "ember-cli-babel": {
+      disableDecoratorTransforms: true,
+    },
+  },
+
   // return an empty tree here as we do not want the addon modules to be
   // included into vendor.js; instead, we will produce a separate bundle
   // (admin.js) to be included via a script tag as needed

app/assets/javascripts/dialog-holder/index.js

@@ -3,6 +3,23 @@
 module.exports = {
   name: require("./package").name,
 
+  options: {
+    babel: {
+      plugins: [
+        [
+          require.resolve("decorator-transforms"),
+          {
+            runEarly: true,
+          },
+        ],
+      ],
+    },
+
+    "ember-cli-babel": {
+      disableDecoratorTransforms: true,
+    },
+  },
+
   isDevelopingAddon() {
     return true;
   },

app/assets/javascripts/discourse-common/index.js

@@ -8,6 +8,21 @@ module.exports = {
         handlebars: "handlebars/dist/cjs/handlebars.js",
       },
     },
+
+    babel: {
+      plugins: [
+        [
+          require.resolve("decorator-transforms"),
+          {
+            runEarly: true,
+          },
+        ],
+      ],
+    },
+
+    "ember-cli-babel": {
+      disableDecoratorTransforms: true,
+    },
   },
 
   isDevelopingAddon() {

app/assets/javascripts/discourse-plugins/index.js

@@ -97,11 +97,20 @@ module.exports = {
 
   options: {
     babel: {
-      plugins: [require.resolve("deprecation-silencer")],
+      plugins: [
+        require.resolve("deprecation-silencer"),
+        [
+          require.resolve("decorator-transforms"),
+          {
+            runEarly: true,
+          },
+        ],
+      ],
     },
 
     "ember-cli-babel": {
       throwUnlessParallelizable: true,
+      disableDecoratorTransforms: true,
     },
 
     "ember-this-fallback": {

app/assets/javascripts/discourse/app/app.js

@@ -1,4 +1,5 @@
 /* eslint-disable simple-import-sort/imports */
+import "decorator-transforms/globals";
 import "./loader-shims";
 import "./global-compat";
 /* eslint-enable simple-import-sort/imports */

app/assets/javascripts/discourse/ember-cli-build.js

@@ -60,10 +60,20 @@ module.exports = function (defaults) {
 
     "ember-cli-babel": {
       throwUnlessParallelizable: true,
+      disableDecoratorTransforms: true,
     },
 
     babel: {
-      plugins: [require.resolve("deprecation-silencer")],
+      sourceMaps: false,
+      plugins: [
+        require.resolve("deprecation-silencer"),
+        [
+          require.resolve("decorator-transforms"),
+          {
+            runEarly: true,
+          },
+        ],
+      ],
     },
 
     vendorFiles: {

app/assets/javascripts/discourse/tests/setup-tests.js

@@ -1,4 +1,5 @@
 /* eslint-disable simple-import-sort/imports */
+import Application from "../app";
 import "./loader-shims";
 /* eslint-enable simple-import-sort/imports */
 
@@ -46,7 +47,6 @@ import deprecated from "discourse-common/lib/deprecated";
 import { setDefaultOwner } from "discourse-common/lib/get-owner";
 import { setupS3CDN, setupURL } from "discourse-common/lib/get-url";
 import { buildResolver } from "discourse-common/resolver";
-import Application from "../app";
 import { loadSprites } from "../lib/svg-sprite-loader";
 import * as FakerModule from "@faker-js/faker";
 import { setLoadedFaker } from "discourse/lib/load-faker";

app/assets/javascripts/float-kit/index.js

@@ -2,7 +2,22 @@
 
 module.exports = {
   name: require("./package").name,
-  options: {},
+  options: {
+    babel: {
+      plugins: [
+        [
+          require.resolve("decorator-transforms"),
+          {
+            runEarly: true,
+          },
+        ],
+      ],
+    },
+
+    "ember-cli-babel": {
+      disableDecoratorTransforms: true,
+    },
+  },
   isDevelopingAddon() {
     return true;
   },

app/assets/javascripts/pretty-text/index.js

@@ -3,6 +3,23 @@
 module.exports = {
   name: require("./package").name,
 
+  options: {
+    babel: {
+      plugins: [
+        [
+          require.resolve("decorator-transforms"),
+          {
+            runEarly: true,
+          },
+        ],
+      ],
+    },
+
+    "ember-cli-babel": {
+      disableDecoratorTransforms: true,
+    },
+  },
+
   isDevelopingAddon() {
     return true;
   },

app/assets/javascripts/select-kit/index.js

@@ -2,7 +2,22 @@
 
 module.exports = {
   name: require("./package").name,
-  options: {},
+  options: {
+    babel: {
+      plugins: [
+        [
+          require.resolve("decorator-transforms"),
+          {
+            runEarly: true,
+          },
+        ],
+      ],
+    },
+
+    "ember-cli-babel": {
+      disableDecoratorTransforms: true,
+    },
+  },
   isDevelopingAddon() {
     return true;
   },

app/assets/javascripts/theme-transpiler/package.json

@@ -19,7 +19,8 @@
     "handlebars": "^4.7.8",
     "path-browserify": "^1.0.1",
     "polyfill-crypto.getrandomvalues": "^1.0.0",
-    "terser": "^5.31.0"
+    "terser": "^5.31.0",
+    "decorator-transforms": "^2.0.0"
   },
   "engines": {
     "node": ">= 18",

app/assets/javascripts/theme-transpiler/transpiler.js

@@ -19,6 +19,7 @@ globalThis.console = {
 import { transform as babelTransform } from "@babel/standalone";
 import HTMLBarsInlinePrecompile from "babel-plugin-ember-template-compilation";
 import { Preprocessor } from "content-tag";
+import DecoratorTransforms from "decorator-transforms";
 import colocatedBabelPlugin from "ember-cli-htmlbars/lib/colocated-babel-plugin";
 import { precompile } from "ember-source/dist/ember-template-compiler";
 import EmberThisFallback from "ember-this-fallback";
@@ -138,6 +139,8 @@ globalThis.transpile = function (source, options = {}) {
   if (moduleId && !skipModule) {
     plugins.push(["transform-modules-amd", { noInterop: true }]);
   }
+  commonPlugins.find((p) => p[0] === "decorator-transforms")[0] =
+    DecoratorTransforms;
   plugins.push(...commonPlugins);
 
   try {

app/models/theme.rb

@@ -6,7 +6,7 @@ require "json_schemer"
 class Theme < ActiveRecord::Base
   include GlobalPath
 
-  BASE_COMPILER_VERSION = 81
+  BASE_COMPILER_VERSION = 82
 
   class SettingsMigrationError < StandardError
   end

lib/discourse_js_processor.rb

@@ -9,9 +9,7 @@ class DiscourseJsProcessor
   # 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",
+    ["decorator-transforms", { runEarly: true }],
     "proposal-class-static-block",
     "transform-parameters",
     "proposal-export-namespace-from",

patches/decorator-transforms+2.0.0.patch

@@ -0,0 +1,21 @@
+diff --git a/node_modules/decorator-transforms/dist/index.js b/node_modules/decorator-transforms/dist/index.js
+index fce3aeb..c23d8e4 100644
+--- a/node_modules/decorator-transforms/dist/index.js
++++ b/node_modules/decorator-transforms/dist/index.js
+@@ -4,10 +4,13 @@ import {
+ import "./chunk-CSAU5B4Q.js";
+ 
+ // src/index.ts
+-import { createRequire } from "module";
++
+ import { ImportUtil } from "babel-import-util";
+-var req = createRequire(import.meta.url);
+-var { default: decoratorSyntax } = req("@babel/plugin-syntax-decorators");
++
++// https://github.com/ef4/decorator-transforms/pull/27
++import PluginSyntaxDecorators from "@babel/plugin-syntax-decorators";
++const decoratorSyntax = PluginSyntaxDecorators.default || PluginSyntaxDecorators;
++
+ function makeVisitor(babel) {
+   const t = babel.types;
+   return {

spec/lib/discourse_js_processor_spec.rb

@@ -92,7 +92,7 @@ RSpec.describe DiscourseJsProcessor do
     JS
 
     result = DiscourseJsProcessor.transpile(script, "blah", "blah/mymodule")
-    expect(result).to include("_applyDecoratedDescriptor")
+    expect(result).to include("static #_ = dt7948.n")
   end
 
   it "correctly transpiles widget hbs" do

spec/lib/theme_javascript_compiler_spec.rb

@@ -251,7 +251,7 @@ RSpec.describe ThemeJavascriptCompiler do
       expect(compiler.raw_content).to include(
         "define(\"discourse/theme-1/discourse/components/my-component\", [\"exports\",",
       )
-      expect(compiler.raw_content).to include("_defineProperty(this, \"value\", \"foo\");")
+      expect(compiler.raw_content).to include('value = "foo";')
       expect(compiler.raw_content).to include("setComponentTemplate")
       expect(compiler.raw_content).to include("createTemplateFactory")
     end