parcel-bundler · marcins · Jul 31, 2023 · Jun 14, 2023 · Jun 14, 2023 · Jun 19, 2023
diff --git a/packages/core/core/src/AssetGraph.js b/packages/core/core/src/AssetGraph.js
@@ -353,10 +353,12 @@ export default class AssetGraph extends ContentGraph<AssetGraphNode> {
         nodeId !== traversedNodeId
       ) {
         if (!ctx?.hasDeferred) {
+          this.safeToIncrementallyBundle = false;
           delete traversedNode.hasDeferred;
         }
         actions.skipChildren();
       } else if (traversedNode.type === 'dependency') {
+        this.safeToIncrementallyBundle = false;
         traversedNode.hasDeferred = false;
       } else if (nodeId !== traversedNodeId) {
         actions.skipChildren();

diff --git a/packages/core/core/src/BundleGraph.js b/packages/core/core/src/BundleGraph.js
@@ -1936,6 +1936,10 @@ export default class BundleGraph {
       bundle.id + bundle.target.publicUrl + this.getContentHash(bundle),
     );
 
+    if (bundle.isPlaceholder) {
+      hash.writeString('placeholder');
+    }
+
     let inlineBundles = this.getInlineBundles(bundle);
     for (let inlineBundle of inlineBundles) {
       hash.writeString(this.getContentHash(inlineBundle));

diff --git a/packages/core/integration-tests/test/integration/lazy-compile/index-sync-async.js b/packages/core/integration-tests/test/integration/lazy-compile/index-sync-async.js
@@ -0,0 +1,11 @@
+export default () => {
+    return Promise.all([
+import('./uses-static-component').then(c => {
+    return c.default()();
+}),
+import('./uses-static-component-async').then(c => {
+    return c.default();
+}).then(s => {
+    return s();
+})]);
+}
diff --git a/packages/core/integration-tests/test/integration/lazy-compile/index.html b/packages/core/integration-tests/test/integration/lazy-compile/index.html
@@ -0,0 +1,12 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+    <meta charset="UTF-8">
+    <meta http-equiv="X-UA-Compatible" content="IE=edge">
+    <meta name="viewport" content="width=device-width, initial-scale=1.0">
+    <title>Document</title>
+</head>
+<body>
+    <script src="./index.js" type="module"></script>
+</body>
+</html>
diff --git a/packages/core/integration-tests/test/integration/lazy-compile/index.js b/packages/core/integration-tests/test/integration/lazy-compile/index.js
@@ -0,0 +1,7 @@
+async function main() {
+    const m = await import('./lazy-1');
+    await import('./parallel-lazy-1');
+    return m.default();
+}
+
+main();
diff --git a/packages/core/integration-tests/test/integration/lazy-compile/lazy-1.js b/packages/core/integration-tests/test/integration/lazy-compile/lazy-1.js
@@ -0,0 +1,4 @@
+export default async () => {
+    const { world } = await import('./lazy-2');
+    return `Hello ${world}`;
+}
diff --git a/packages/core/integration-tests/test/integration/lazy-compile/lazy-2.js b/packages/core/integration-tests/test/integration/lazy-compile/lazy-2.js
@@ -0,0 +1 @@
+export const world = 'world';
diff --git a/packages/core/integration-tests/test/integration/lazy-compile/package.json b/packages/core/integration-tests/test/integration/lazy-compile/package.json
@@ -0,0 +1,3 @@
+{
+    "private": true
+}
diff --git a/packages/core/integration-tests/test/integration/lazy-compile/parallel-lazy-1.js b/packages/core/integration-tests/test/integration/lazy-compile/parallel-lazy-1.js
@@ -0,0 +1,4 @@
+export default async () => {
+    const m = await import('./parallel-lazy-2');
+    return m.default;
+};
diff --git a/packages/core/integration-tests/test/integration/lazy-compile/parallel-lazy-2.js b/packages/core/integration-tests/test/integration/lazy-compile/parallel-lazy-2.js
@@ -0,0 +1 @@
+export default 'parallel lazy 2';
diff --git a/packages/core/integration-tests/test/integration/lazy-compile/static-component.js b/packages/core/integration-tests/test/integration/lazy-compile/static-component.js
@@ -0,0 +1 @@
+export default () => "static component";
diff --git a/packages/core/integration-tests/test/integration/lazy-compile/uses-static-component-async.js b/packages/core/integration-tests/test/integration/lazy-compile/uses-static-component-async.js
@@ -0,0 +1,4 @@
+export default async () => {
+    const m = await import('./static-component');
+    return m.default;
+}
diff --git a/packages/core/integration-tests/test/integration/lazy-compile/uses-static-component.js b/packages/core/integration-tests/test/integration/lazy-compile/uses-static-component.js
@@ -0,0 +1,4 @@
+import staticComponent  from "./static-component"
+export default () => {
+    return staticComponent;
+}
diff --git a/packages/core/integration-tests/test/lazy-compile.js b/packages/core/integration-tests/test/lazy-compile.js
@@ -0,0 +1,123 @@
+import assert from 'assert';
+import path from 'path';
+import {
+  bundler,
+  outputFS,
+  distDir,
+  getNextBuild,
+  assertBundles,
+  removeDistDirectory,
+  run,
+} from '@parcel/test-utils';
+
+const findBundle = (bundleGraph, nameRegex) => {
+  return bundleGraph.getBundles().find(b => nameRegex.test(b.name));
+};
+
+const distDirIncludes = async matches => {
+  const files = await outputFS.readdir(distDir);
+  for (const match of matches) {
+    if (typeof match === 'string') {
+      if (!files.some(file => file === match)) {
+        throw new Error(
+          `No file matching ${match} was found in ${files.join(', ')}`,
+        );
+      }
+    } else {
+      if (!files.some(file => match.test(file))) {
+        throw new Error(
+          `No file matching ${match} was found in ${files.join(', ')}`,
+        );
+      }
+    }
+  }
+  return true;
+};
+
+describe('lazy compile', function () {
+  it('should lazy compile', async function () {
+    const b = await bundler(
+      path.join(__dirname, '/integration/lazy-compile/index.js'),
+      {
+        shouldBuildLazily: true,
+        mode: 'development',
+        shouldContentHash: false,
+      },
+    );
+
+    await removeDistDirectory();
+
+    const subscription = await b.watch();
+    let result = await getNextBuild(b);
+
+    // This simulates what happens if index.js is loaded as well as lazy-1 which loads lazy-2.
+    // While parallel-lazy-1 is also async imported by index.js, we pretend it wasn't requested (i.e. like
+    // if it was behind a different trigger).
+    result = await result.requestBundle(
+      findBundle(result.bundleGraph, /index.js/),
+    );
+    result = await result.requestBundle(
+      findBundle(result.bundleGraph, /^lazy-1/),
+    );
+    result = await result.requestBundle(
+      findBundle(result.bundleGraph, /^lazy-2/),
+    );
+
+    // Expect the bundle graph to contain the whole nest of lazy from `lazy-1`, but not
+    // `parallel-lazy-1` which wasn't requested.
+    assertBundles(result.bundleGraph, [
+      {
+        assets: ['index.js', 'bundle-url.js', 'cacheLoader.js', 'js-loader.js'],
+      },
+      {
+        assets: ['lazy-1.js', 'esmodule-helpers.js'],
+      },
+      {
+        assets: ['lazy-2.js'],
+      },
+      {
+        assets: ['parallel-lazy-1.js'],
+      },
+    ]);
+
+    subscription.unsubscribe();
+
+    // Ensure the files match the bundle graph - lazy-2 should've been produced as it was requested
+    assert(await distDirIncludes(['index.js', /^lazy-1\./, /^lazy-2\./]));
+  });
+
+  it('should lazy compile properly when same module is used sync/async', async () => {
   // Also do this when building lazily or the runtime itself could get deduplicated and only 
   // exist in the parent. This causes errors if an old version of the parent without the runtime 
   // is already loaded. 
   if ( 
     bundle.env.outputFormat === 'commonjs' || 
     bundle.env.isLibrary || 
     options.shouldBuildLazily 
   ) { 
     externalBundles = [mainBundle]; 
   } else { 
   // Also do this when building lazily or the runtime itself could get deduplicated and only 
   // exist in the parent. This causes errors if an old version of the parent without the runtime 
   // is already loaded. 
   if ( 
     bundle.env.outputFormat === 'commonjs' || 
     bundle.env.isLibrary || 
     options.shouldBuildLazily 
   ) { 
     externalBundles = [mainBundle]; 
   } else { 
+    const b = await bundler(
+      path.join(__dirname, '/integration/lazy-compile/index-sync-async.js'),
+      {
+        shouldBuildLazily: true,
+        mode: 'development',
+        shouldContentHash: false,
+      },
+    );
+
+    await removeDistDirectory();
+
+    const subscription = await b.watch();
+    let result = await getNextBuild(b);
+    result = await result.requestBundle(
+      findBundle(result.bundleGraph, /^index-sync-async\./),
+    );
+    result = await result.requestBundle(
+      findBundle(result.bundleGraph, /^uses-static-component\./),
+    );
+    result = await result.requestBundle(
+      findBundle(result.bundleGraph, /^uses-static-component-async\./),
+    );
+    result = await result.requestBundle(
+      findBundle(result.bundleGraph, /^static-component\./),
+    );
+
+    let output = await run(result.bundleGraph);
+    assert.deepEqual(await output.default(), [
+      'static component',
+      'static component',
+    ]);
+    subscription.unsubscribe();
+  });
+});
diff --git a/packages/runtimes/js/src/JSRuntime.js b/packages/runtimes/js/src/JSRuntime.js
@@ -357,14 +357,13 @@ function getLoaderRuntime({
   // Importing of the other bundles will be handled by the bundle group entry.
   // Do the same thing in library mode for ES modules, as we are building for another bundler
   // and the imports for sibling bundles will be in the target bundle.
-  // Also do this when building lazily or the runtime itself could get deduplicated and only
-  // exist in the parent. This causes errors if an old version of the parent without the runtime
-  // is already loaded.
-  if (
-    bundle.env.outputFormat === 'commonjs' ||
-    bundle.env.isLibrary ||
-    options.shouldBuildLazily
-  ) {
+
+  // Previously we also did this when building lazily, however it seemed to cause issues in some cases.
+  // The original comment as to why is left here, in case a future traveller is trying to fix that issue:
+  // > [...] the runtime itself could get deduplicated and only exist in the parent. This causes errors if an
+  // > old version of the parent without the runtime
+  // > is already loaded.
+  if (bundle.env.outputFormat === 'commonjs' || bundle.env.isLibrary) {
     externalBundles = [mainBundle];
   } else {
     // Otherwise, load the bundle group entry after the others.
@@ -443,7 +442,9 @@ function getLoaderRuntime({
     loaderModules.push(code);
   }
 
-  if (bundle.env.context === 'browser' && !options.shouldBuildLazily) {
+  // Similar to the comment above, this also used to be skipped when shouldBuildLazily was true,
+  // however it caused issues where a bundle group contained multiple bundles.
+  if (bundle.env.context === 'browser') {
     loaderModules.push(
       ...externalBundles
         // TODO: Allow css to preload resources as well