fix: add support to emit decorator metadata (#119)

.gitignore

@@ -1,3 +1,4 @@
+.idea
 node_modules
 dist
 *.log*

package.json

@@ -45,6 +45,7 @@
     "acorn": "^8.8.2",
     "babel-plugin-dynamic-import-node": "^2.3.3",
     "babel-plugin-parameter-decorator": "^1.0.16",
+    "babel-plugin-transform-typescript-metadata": "^0.3.2",
     "changelogen": "^0.4.1",
     "config": "^3.3.9",
     "create-require": "^1.1.1",
@@ -63,11 +64,13 @@
     "pirates": "^4.0.5",
     "pkg-types": "^1.0.2",
     "prettier": "^2.8.4",
+    "reflect-metadata": "^0.1.13",
     "semver": "^7.3.8",
     "terser-webpack-plugin": "^5.3.6",
     "ts-loader": "^9.4.2",
     "tslib": "^2.5.0",
     "typescript": "^4.9.5",
+    "vite": "^4.1.2",
     "vitest": "^0.28.5",
     "webpack": "^5.75.0",
     "webpack-cli": "^5.0.1"

src/babel.ts

@@ -33,11 +33,11 @@ export default function transform(opts: TransformOptions): TRANSFORM_RESULT {
       require("@babel/plugin-transform-typescript"),
       { allowDeclareFields: true },
     ]);
-    // `unshift` because this plugin must come before `@babel/plugin-syntax-class-properties`
-    _opts.plugins.unshift([
-      require("@babel/plugin-proposal-decorators"),
-      { legacy: true },
-    ]);
+    // `unshift` because these plugin must come before `@babel/plugin-syntax-class-properties`
+    _opts.plugins.unshift(
+      [require("babel-plugin-transform-typescript-metadata")],
+      [require("@babel/plugin-proposal-decorators"), { legacy: true }]
+    );
     _opts.plugins.push(require("babel-plugin-parameter-decorator"));
     _opts.plugins.push(require("@babel/plugin-syntax-import-assertions"));
   }

test/__snapshots__/fixtures.test.ts.snap

@@ -106,9 +106,14 @@ Logical nullish assignment: 50 20"
 `;
 
 exports[`fixtures > typescript > stdout 1`] = `
-"{
+"Decorator metadata keys: design:type
+Decorator called with 3 arguments.
+Decorator called with 3 arguments.
+Decorator called with 3 arguments.
+Decorator called with 1 arguments.
+{
   file: '<cwd>/test.ts',
   dir: '<cwd>',
   resolve: '<cwd>/test.ts'
-} undefined"
+} undefined [class DecoratedClass]"
 `;

test/fixtures/typescript/decorators.ts

@@ -1,11 +1,21 @@
+import "reflect-metadata";
 function decorator(...args: any) {
-  console.log("Decorator called with arguments:", args);
+  console.log("Decorator called with " + args.length + " arguments.");
+}
+
+function anotherDecorator() {
+  return function (object: any, propertyName: any) {
+    console.log(
+      "Decorator metadata keys: " +
+        Reflect.getMetadataKeys(object, propertyName)
+    );
+  };
 }
 
 @decorator
 export default class DecoratedClass {
-  @decorator
-  decoratedProperty = null;
+  @anotherDecorator()
+  decoratedProperty: string;
 
   @decorator
   get decoratedAccessor() {
@@ -16,4 +26,8 @@ export default class DecoratedClass {
   decoratedFunction(@decorator decoratedParameter: any) {
     return decoratedParameter;
   }
+
+  constructor() {
+    this.decoratedProperty = "foo";
+  }
 }

test/fixtures/typescript/index.ts

@@ -1,4 +1,5 @@
 import test, { FeedService } from "./test";
+import Clazz from "./decorators";
 export type { Test } from "./types";
 
-console.log(test(), FeedService);
+console.log(test(), FeedService, Clazz);