feat(vite): get rid of unnecessary polyfills (#3242)

Author: marvinhagemeister

packages/plugin-vite/src/plugins/patches.ts

@@ -4,6 +4,7 @@ import { cjsPlugin } from "./patches/commonjs.ts";
 import { jsxComments } from "./patches/jsx_comment.ts";
 import babelReact from "@babel/preset-react";
 import { inlineEnvVarsPlugin } from "./patches/inline_env_vars.ts";
+import { removePolyfills } from "./patches/remove_polyfills.ts";
 
 export function patches(): Plugin {
   let isDev = false;
@@ -33,6 +34,7 @@ export function patches(): Plugin {
         babelrc: false,
         plugins: [
           cjsPlugin,
+          removePolyfills,
           jsxComments,
           inlineEnvVarsPlugin(
             isDev ? "development" : "production",

packages/plugin-vite/src/plugins/patches/remove_polyfills.ts

@@ -0,0 +1,32 @@
+import type { PluginObj, types } from "@babel/core";
+
+export function removePolyfills(
+  { types: t }: { types: typeof types },
+): PluginObj {
+  return {
+    name: "fresh-remove-polyfills",
+    visitor: {
+      IfStatement(path) {
+        if (
+          t.isUnaryExpression(path.node.test) &&
+          path.node.test.operator === "!" &&
+          t.isMemberExpression(path.node.test.argument) &&
+          t.isIdentifier(path.node.test.argument.object) &&
+          ((path.node.test.argument.object.name === "String" &&
+            t.isIdentifier(path.node.test.argument.property) &&
+            path.node.test.argument.property.name === "fromCodePoint") ||
+            (path.node.test.argument.object.name === "Object" &&
+              t.isIdentifier(path.node.test.argument.property) &&
+              (path.node.test.argument.property.name === "keys" ||
+                path.node.test.argument.property.name === "create")))
+        ) {
+          if (path.node.alternate) {
+            path.replaceWith(t.cloneNode(path.node.alternate, true));
+          } else {
+            path.remove();
+          }
+        }
+      },
+    },
+  };
+}

packages/plugin-vite/src/plugins/patches/remove_polyfills_test.ts

@@ -0,0 +1,87 @@
+import { expect } from "@std/expect/expect";
+import * as babel from "@babel/core";
+import { removePolyfills } from "./remove_polyfills.ts";
+
+function runTest(options: { input: string; expected: string }) {
+  const res = babel.transformSync(options.input, {
+    filename: "foo.js",
+    babelrc: false,
+    plugins: [removePolyfills],
+  });
+
+  const output = res?.code ?? "";
+  expect(output).toEqual(options.expected);
+}
+
+Deno.test("remove polyfills - Object.keys", () => {
+  runTest({
+    input: `if (!Object.keys) {
+    Object.keys = function (o) {
+    var a = []
+    for (var i in o) if (o.hasOwnProperty(i)) a.push(i)
+    return a
+  }
+}
+
+Object.keys({ foo: "bar" });`,
+    expected: `Object.keys({
+  foo: "bar"
+});`,
+  });
+});
+
+Deno.test("remove polyfills - Object.create", () => {
+  runTest({
+    input: `if (!Object.create) {
+  Object.create = function (o) {
+    function F () {}
+    F.prototype = o
+    var newf = new F()
+    return newf
+  }
+}
+
+Object.create({});`,
+    expected: `Object.create({});`,
+  });
+});
+
+Deno.test("remove polyfills - keep alternate", () => {
+  runTest({
+    input: `if (!Object.create) {
+  Object.create = function (o) {
+    function F () {}
+    F.prototype = o
+    var newf = new F()
+    return newf
+  }
+} else {
+  console.log("foo")
+}`,
+    expected: `{
+  console.log("foo");
+}`,
+  });
+});
+
+Deno.test("remove polyfills - String.fromCodePoint", () => {
+  runTest({
+    input: `if (!String.fromCodePoint) {
+  foo
+}
+  
+String.fromCodePoint(42);`,
+    expected: `String.fromCodePoint(42);`,
+  });
+});
+
+Deno.test("remove polyfills - Keep unrelated unary statements", () => {
+  runTest({
+    input: `if (+String.fromCodePoint) {
+  foo;
+}`,
+    expected: `if (+String.fromCodePoint) {
+  foo;
+}`,
+  });
+});