fix: optimize nested index-only deps (#282)

Author: bluwy

.changeset/gold-drinks-peel.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/vite-plugin-svelte': patch
+---
+
+Optimize nested index-only dependencies

packages/e2e-tests/_test_dependencies/index-only/index.js

@@ -0,0 +1 @@
+module.exports = 'foo';

packages/e2e-tests/_test_dependencies/index-only/package.json

@@ -0,0 +1,8 @@
+{
+  "version": "1.0.0",
+  "private": true,
+  "name": "e2e-test-dep-index-only",
+  "files": [
+    "index.js"
+  ]
+}

packages/e2e-tests/_test_dependencies/types-only/index.d.ts

@@ -0,0 +1 @@
+export function foo(): string;

packages/e2e-tests/_test_dependencies/types-only/package.json

@@ -0,0 +1,9 @@
+{
+  "version": "1.0.0",
+  "private": true,
+  "name": "e2e-test-dep-types-only",
+  "types": "./index.d.ts",
+  "files": [
+    "index.d.ts"
+  ]
+}

packages/e2e-tests/dependencies/package.json

@@ -0,0 +1,13 @@
+{
+  "name": "e2e-tests-dependencies",
+  "description": "Used by dependencies.spec.ts",
+  "private": true,
+  "version": "0.0.0",
+  "dependencies": {
+    "e2e-test-dep-cjs-and-esm": "workspace:*",
+    "e2e-test-dep-cjs-only": "workspace:*",
+    "e2e-test-dep-esm-only": "workspace:*",
+    "e2e-test-dep-index-only": "workspace:*",
+    "e2e-test-dep-scss-only": "workspace:*"
+  }
+}

packages/vite-plugin-svelte/src/utils/__tests__/dependencies.spec.ts

@@ -1,15 +1,16 @@
-import { findRootSvelteDependencies } from '../dependencies';
+import { findRootSvelteDependencies, needsOptimization } from '../dependencies';
 import * as path from 'path';
+import { createRequire } from 'module';
 
 describe('dependencies', () => {
 	describe('findRootSvelteDependencies', () => {
-		it('should find svelte dependencies in packages/e2e-test/hmr', async () => {
+		it('should find svelte dependencies in packages/e2e-test/hmr', () => {
 			const deps = findRootSvelteDependencies(path.resolve('packages/e2e-tests/hmr'));
 			expect(deps).toHaveLength(1);
 			expect(deps[0].name).toBe('e2e-test-dep-svelte-simple');
 			expect(deps[0].path).toEqual([]);
 		});
-		it('should find nested svelte dependencies in packages/e2e-test/package-json-svelte-field', async () => {
+		it('should find nested svelte dependencies in packages/e2e-test/package-json-svelte-field', () => {
 			const deps = findRootSvelteDependencies(
 				path.resolve('packages/e2e-tests/package-json-svelte-field')
 			);
@@ -26,4 +27,14 @@ describe('dependencies', () => {
 			expect(simple.path[0]).toBe('e2e-test-dep-svelte-nested');
 		});
 	});
+	describe('needsOptimization', () => {
+		it('should optimize cjs deps only', () => {
+			const localRequire = createRequire(path.resolve('packages/e2e-tests/dependencies'));
+			expect(needsOptimization('e2e-test-dep-cjs-and-esm', localRequire)).toBe(false);
+			expect(needsOptimization('e2e-test-dep-cjs-only', localRequire)).toBe(true);
+			expect(needsOptimization('e2e-test-dep-esm-only', localRequire)).toBe(false);
+			expect(needsOptimization('e2e-test-dep-index-only', localRequire)).toBe(true);
+			expect(needsOptimization('e2e-test-dep-types-only', localRequire)).toBe(false);
+		});
+	});
 });

packages/vite-plugin-svelte/src/utils/dependencies.ts

@@ -187,12 +187,23 @@ export function needsOptimization(dep: string, localRequire: NodeRequire): boole
 	const pkg = depData.pkg;
 	// only optimize if is cjs, using the below as heuristic
 	// see https://github.com/sveltejs/vite-plugin-svelte/issues/162
-	const isCjs = pkg.main && !pkg.module && !pkg.exports;
-	if (!isCjs) return false;
-	// ensure entry is js so vite can prebundle it
-	// see https://github.com/sveltejs/vite-plugin-svelte/issues/233
-	const entryExt = path.extname(pkg.main);
-	return !entryExt || entryExt === '.js' || entryExt === '.cjs';
+	const hasEsmFields = pkg.module || pkg.exports;
+	if (hasEsmFields) return false;
+	if (pkg.main) {
+		// ensure entry is js so vite can prebundle it
+		// see https://github.com/sveltejs/vite-plugin-svelte/issues/233
+		const entryExt = path.extname(pkg.main);
+		return !entryExt || entryExt === '.js' || entryExt === '.cjs';
+	} else {
+		// check if has implicit index.js entrypoint
+		// https://github.com/sveltejs/vite-plugin-svelte/issues/281
+		try {
+			localRequire.resolve(`${dep}/index.js`);
+			return true;
+		} catch {
+			return false;
+		}
+	}
 }
 
 interface DependencyData {