fix: don't optimize in with syntheticNamedExports

rollup · lukastaegert · Aug 20, 2025 · Aug 2, 2025 · Aug 2, 2025 · Aug 18, 2025
commit a39ebadf90ee9d3248b1ec561a342c84ffbeefc1
diff --git a/src/ast/nodes/BinaryExpression.ts b/src/ast/nodes/BinaryExpression.ts
@@ -15,6 +15,7 @@ import {
 import { getRenderedLiteralValue } from '../utils/renderLiteralValue';
 import ExternalVariable from '../variables/ExternalVariable';
 import NamespaceVariable from '../variables/NamespaceVariable';
+import SyntheticNamedExportVariable from '../variables/SyntheticNamedExportVariable';
 import ExpressionStatement from './ExpressionStatement';
 import type { LiteralValue } from './Literal';
 import type * as NodeType from './NodeType';
@@ -109,6 +110,7 @@ export default class BinaryExpression extends NodeBase implements DeoptimizableE
 		if (this.operator === 'in' && this.right.variable instanceof NamespaceVariable) {
 			const [variable] = this.right.variable.context.traceExport(String(leftValue));
 			if (variable instanceof ExternalVariable) return UnknownValue;
+			if (variable instanceof SyntheticNamedExportVariable) return UnknownValue;
 			return !!variable;
 		}
 

diff --git a/test/form/samples/namespace-optimization-in-operator-synthetic/_config.js b/test/form/samples/namespace-optimization-in-operator-synthetic/_config.js
@@ -0,0 +1,27 @@
+module.exports = defineTest({
+	description: 'disables optimization for synthetic named exports when using the in operator',
+	options: {
+		plugins: [
+			{
+				name: 'virtual-synthatic',
+				resolveId(id) {
+					if (id === 'virtual:synthetic') {
+						return '\0' + id;
+					}
+				},
+				load(id) {
+					if (id === '\0virtual:synthetic') {
+						const code = `
+							export const __moduleExports = { a: true };
+						`;
+						return {
+							code,
+							syntheticNamedExports: '__moduleExports'
+						};
+					}
+				}
+			}
+		]
+	},
+	solo: true
+});
diff --git a/test/form/samples/namespace-optimization-in-operator-synthetic/_expected.js b/test/form/samples/namespace-optimization-in-operator-synthetic/_expected.js
@@ -0,0 +1,23 @@
+function _mergeNamespaces(n, m) {
+	m.forEach(function (e) {
+		e && typeof e !== 'string' && !Array.isArray(e) && Object.keys(e).forEach(function (k) {
+			if (k !== 'default' && !(k in n)) {
+				var d = Object.getOwnPropertyDescriptor(e, k);
+				Object.defineProperty(n, k, d.get ? d : {
+					enumerable: true,
+					get: function () { return e[k]; }
+				});
+			}
+		});
+	});
+	return Object.freeze(n);
+}
+
+const __moduleExports = { a: true };
+
+var mod = /*#__PURE__*/_mergeNamespaces({
+	__proto__: null
+}, [__moduleExports]);
+
+if ('a' in mod) console.log(`'a' in mod`);
+if ('b' in mod) console.log(`'b' in mod`);
diff --git a/test/form/samples/namespace-optimization-in-operator-synthetic/main.js b/test/form/samples/namespace-optimization-in-operator-synthetic/main.js
@@ -0,0 +1,4 @@
+import * as mod from 'virtual:synthetic';
+
+if ('a' in mod) console.log(`'a' in mod`)
+if ('b' in mod) console.log(`'b' in mod`)