From f84949f98d37ccfd4b28b131ca77eaf8ff30c030 Mon Sep 17 00:00:00 2001
From: Colin Rotherham <work@colinr.com>
Date: Tue, 24 Oct 2023 10:19:51 +0100
Subject: [PATCH] Add Babel polyfill provider ES shims

Rollup will log a warning for code requiring polyfills:

> (!) Unresolved dependencies
> https://rollupjs.org/troubleshooting/#warning-treating-module-as-external-dependency
> error-cause/Error (imported by "src/govuk/errors/index.mjs")

Babel will also log a warning:

> Some polyfills have been added but are not present in your dependencies.
>
> Please run one of the following commands:
> 	npm install --save error-cause@^1.0.1
> 	yarn add error-cause@^1.0.1

See ES shims on GitHub: https://github.com/es-shims
---
 package-lock.json                       | 13 +++++++++++++
 packages/govuk-frontend/babel.config.js | 14 ++++++++++++++
 packages/govuk-frontend/package.json    |  1 +
 3 files changed, 28 insertions(+)

diff --git a/package-lock.json b/package-lock.json
index 048aaa8201..bedec78ed9 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -6427,6 +6427,18 @@
         "@babel/core": "^7.4.0 || ^8.0.0-0 <8.0.0"
       }
     },
+    "node_modules/babel-plugin-polyfill-es-shims": {
+      "version": "0.10.0",
+      "resolved": "https://registry.npmjs.org/babel-plugin-polyfill-es-shims/-/babel-plugin-polyfill-es-shims-0.10.0.tgz",
+      "integrity": "sha512-+wJQdSNHoLrEbCUIzyMXEZd55EyBOqRdMB2JtBMgk9rXpBYdorcW2JT/KXYhbKNYR3bZ6rYvD7ciF42juwZdQA==",
+      "dev": true,
+      "dependencies": {
+        "@babel/helper-define-polyfill-provider": "^0.4.3"
+      },
+      "peerDependencies": {
+        "@babel/core": "^7.4.0 || ^8.0.0-0 <8.0.0"
+      }
+    },
     "node_modules/babel-plugin-polyfill-regenerator": {
       "version": "0.5.3",
       "resolved": "https://registry.npmjs.org/babel-plugin-polyfill-regenerator/-/babel-plugin-polyfill-regenerator-0.5.3.tgz",
@@ -30358,6 +30370,7 @@
         "@rollup/plugin-replace": "^5.0.5",
         "@rollup/plugin-terser": "^0.4.4",
         "autoprefixer": "^10.4.16",
+        "babel-plugin-polyfill-es-shims": "^0.10.0",
         "cssnano": "^6.0.1",
         "cssnano-preset-default": "^6.0.1",
         "govuk-prototype-kit": "^13.13.6",
diff --git a/packages/govuk-frontend/babel.config.js b/packages/govuk-frontend/babel.config.js
index a8d26f7e95..37f484e5c1 100644
--- a/packages/govuk-frontend/babel.config.js
+++ b/packages/govuk-frontend/babel.config.js
@@ -5,6 +5,7 @@
  */
 module.exports = function (api) {
   const isBrowser = !api.env('test')
+  const isProduction = !api.env('development')
 
   // Apply Browserslist environment for supported targets
   // https://github.com/browserslist/browserslist#configuring-for-different-environments
@@ -33,6 +34,19 @@ module.exports = function (api) {
         return !isPrivate && isDocumentation
       }
     },
+    plugins: [
+      [
+        'polyfill-es-shims',
+        {
+          // Add logging for required polyfills
+          debug: isProduction,
+
+          // Replace unsupported code with polyfills
+          // without modifying window globals
+          method: 'usage-pure'
+        }
+      ]
+    ],
     presets: [
       [
         '@babel/preset-env',
diff --git a/packages/govuk-frontend/package.json b/packages/govuk-frontend/package.json
index e7d67d6f74..bbdeda3d98 100644
--- a/packages/govuk-frontend/package.json
+++ b/packages/govuk-frontend/package.json
@@ -73,6 +73,7 @@
     "@rollup/plugin-replace": "^5.0.5",
     "@rollup/plugin-terser": "^0.4.4",
     "autoprefixer": "^10.4.16",
+    "babel-plugin-polyfill-es-shims": "^0.10.0",
     "cssnano": "^6.0.1",
     "cssnano-preset-default": "^6.0.1",
     "govuk-prototype-kit": "^13.13.6",