From 3054d8cf871ed9ea17ce4b0558e27034909ea72d Mon Sep 17 00:00:00 2001
From: David Alsh <12656294+alshdavid@users.noreply.github.com>
Date: Wed, 24 Jul 2024 09:57:33 +1000
Subject: [PATCH] Add retriable dynamic imports behind a feature flag (#9860)

* import retries

* cache result if succesful
---
 packages/core/core/test/test-utils.js         |  1 +
 packages/core/feature-flags/src/index.js      |  1 +
 packages/core/feature-flags/src/types.js      |  4 +++
 packages/runtimes/js/src/JSRuntime.js         | 18 +++++++++++++
 .../helpers/browser/esm-js-loader-retry.js    | 26 +++++++++++++++++++
 5 files changed, 50 insertions(+)
 create mode 100644 packages/runtimes/js/src/helpers/browser/esm-js-loader-retry.js

diff --git a/packages/core/core/test/test-utils.js b/packages/core/core/test/test-utils.js
index 0fa89c3315f..b9331e652f8 100644
--- a/packages/core/core/test/test-utils.js
+++ b/packages/core/core/test/test-utils.js
@@ -55,6 +55,7 @@ export const DEFAULT_OPTIONS: ParcelOptions = {
   featureFlags: {
     exampleFeature: false,
     parcelV3: false,
+    importRetry: false,
   },
 };
 
diff --git a/packages/core/feature-flags/src/index.js b/packages/core/feature-flags/src/index.js
index 4bcc5d71993..96819652129 100644
--- a/packages/core/feature-flags/src/index.js
+++ b/packages/core/feature-flags/src/index.js
@@ -8,6 +8,7 @@ export type FeatureFlags = _FeatureFlags;
 export const DEFAULT_FEATURE_FLAGS: FeatureFlags = {
   exampleFeature: false,
   parcelV3: false,
+  importRetry: false,
 };
 
 let featureFlagValues: FeatureFlags = {...DEFAULT_FEATURE_FLAGS};
diff --git a/packages/core/feature-flags/src/types.js b/packages/core/feature-flags/src/types.js
index fa78c4c7b81..73ef3f63611 100644
--- a/packages/core/feature-flags/src/types.js
+++ b/packages/core/feature-flags/src/types.js
@@ -7,4 +7,8 @@ export type FeatureFlags = {|
    * Rust backed requests
    */
   +parcelV3: boolean,
+  /**
+   * Configure runtime to enable retriable dynamic imports
+   */
+  importRetry: boolean,
 |};
diff --git a/packages/runtimes/js/src/JSRuntime.js b/packages/runtimes/js/src/JSRuntime.js
index d66e1d6b530..f5058c1c542 100644
--- a/packages/runtimes/js/src/JSRuntime.js
+++ b/packages/runtimes/js/src/JSRuntime.js
@@ -484,6 +484,24 @@ function getLoaderRuntime({
     )}'))`;
   }
 
+  if (needsEsmLoadPrelude && options.featureFlags.importRetry) {
+    loaderCode = `
+      Object.defineProperty(module, 'exports', { get: () => {
+        let load = require('./helpers/browser/esm-js-loader-retry');
+        return ${loaderCode}.then((v) => {
+          Object.defineProperty(module, "exports", { value: Promise.resolve(v) })
+          return v
+        });
+      }})`;
+
+    return {
+      filePath: __filename,
+      code: loaderCode,
+      dependency,
+      env: {sourceType: 'module'},
+    };
+  }
+
   let code = [];
 
   if (needsEsmLoadPrelude) {
diff --git a/packages/runtimes/js/src/helpers/browser/esm-js-loader-retry.js b/packages/runtimes/js/src/helpers/browser/esm-js-loader-retry.js
new file mode 100644
index 00000000000..1f729b6b914
--- /dev/null
+++ b/packages/runtimes/js/src/helpers/browser/esm-js-loader-retry.js
@@ -0,0 +1,26 @@
+async function load(id) {
+  if (!parcelRequire.retryState) {
+    parcelRequire.retryState = {};
+  }
+
+  if (!globalThis.navigator.onLine) {
+    await new Promise(res =>
+      globalThis.addEventListener('online', res, {once: true}),
+    );
+  }
+
+  let url = require('../bundle-manifest').resolve(id);
+
+  if (parcelRequire.retryState[id] != undefined) {
+    url = `${url}?retry=${parcelRequire.retryState[id]}`;
+  }
+
+  try {
+    // eslint-disable-next-line no-undef
+    return await __parcel__import__(url);
+  } catch (error) {
+    parcelRequire.retryState[id] = Date.now();
+  }
+}
+
+module.exports = load;