From 7080da6e28987e6291833e7b3830d9481db93cca Mon Sep 17 00:00:00 2001
From: Lukas Taegert-Atkinson <lukas.taegert-atkinson@tngtech.com>
Date: Tue, 29 Jun 2021 21:38:20 +0200
Subject: [PATCH] Properly handle double reexports from external namespaces

---
 src/Module.ts                                 | 21 +++++++++++++++----
 .../double-namespace-reexport/_config.js      | 17 +++++++++++++++
 .../double-namespace-reexport/first.js        |  1 +
 .../samples/double-namespace-reexport/main.js |  1 +
 .../double-namespace-reexport/second.js       |  1 +
 5 files changed, 37 insertions(+), 4 deletions(-)
 create mode 100644 test/function/samples/double-namespace-reexport/_config.js
 create mode 100644 test/function/samples/double-namespace-reexport/first.js
 create mode 100644 test/function/samples/double-namespace-reexport/main.js
 create mode 100644 test/function/samples/double-namespace-reexport/second.js

diff --git a/src/Module.ts b/src/Module.ts
index 494ffc7eef9..7f27f22f156 100644
--- a/src/Module.ts
+++ b/src/Module.ts
@@ -533,12 +533,15 @@ export default class Module {
 			const foundNamespaceReexport =
 				name in this.namespaceReexportsByName
 					? this.namespaceReexportsByName[name]
-					: (this.namespaceReexportsByName[name] = this.getVariableFromNamespaceReexports(
+					: this.getVariableFromNamespaceReexports(
 							name,
 							importerForSideEffects,
 							searchedNamesAndModules,
 							skipExternalNamespaceReexports
-					  ));
+					  );
+			if (!skipExternalNamespaceReexports) {
+				this.namespaceReexportsByName[name] = foundNamespaceReexport;
+			}
 			if (foundNamespaceReexport) {
 				return foundNamespaceReexport;
 			}
@@ -1012,8 +1015,18 @@ export default class Module {
 		skipExternalNamespaceReexports = false
 	): Variable | null {
 		let foundSyntheticDeclaration: SyntheticNamedExportVariable | null = null;
-		const skipExternalNamespaceValues = new Set([true, skipExternalNamespaceReexports]);
-		for (const skipExternalNamespaces of skipExternalNamespaceValues) {
+		const skipExternalNamespaceValues = [{ searchedNamesAndModules, skipExternalNamespaces: true }];
+		if (!skipExternalNamespaceReexports) {
+			const clonedSearchedNamesAndModules = new Map<string, Set<Module | ExternalModule>>();
+			for (const [name, modules] of searchedNamesAndModules || []) {
+				clonedSearchedNamesAndModules.set(name, new Set(modules));
+			}
+			skipExternalNamespaceValues.push({
+				searchedNamesAndModules: clonedSearchedNamesAndModules,
+				skipExternalNamespaces: false
+			});
+		}
+		for (const { skipExternalNamespaces, searchedNamesAndModules } of skipExternalNamespaceValues) {
 			const foundDeclarations = new Set<Variable>();
 			for (const module of this.exportAllModules) {
 				if (module instanceof Module || !skipExternalNamespaces) {
diff --git a/test/function/samples/double-namespace-reexport/_config.js b/test/function/samples/double-namespace-reexport/_config.js
new file mode 100644
index 00000000000..41edda36e9a
--- /dev/null
+++ b/test/function/samples/double-namespace-reexport/_config.js
@@ -0,0 +1,17 @@
+const assert = require('assert');
+
+module.exports = {
+	description: 'handles chained namespace reexports from externals',
+	options: {
+		external: 'external'
+	},
+	context: {
+		require(id) {
+			assert.strictEqual(id, 'external');
+			return { foo: 42 };
+		}
+	},
+	exports({ foo }) {
+		assert.strictEqual(foo, 42);
+	}
+};
diff --git a/test/function/samples/double-namespace-reexport/first.js b/test/function/samples/double-namespace-reexport/first.js
new file mode 100644
index 00000000000..853dbb4b2f2
--- /dev/null
+++ b/test/function/samples/double-namespace-reexport/first.js
@@ -0,0 +1 @@
+export * from './second.js';
diff --git a/test/function/samples/double-namespace-reexport/main.js b/test/function/samples/double-namespace-reexport/main.js
new file mode 100644
index 00000000000..2d9fdc01be5
--- /dev/null
+++ b/test/function/samples/double-namespace-reexport/main.js
@@ -0,0 +1 @@
+export { foo } from './first.js';
diff --git a/test/function/samples/double-namespace-reexport/second.js b/test/function/samples/double-namespace-reexport/second.js
new file mode 100644
index 00000000000..4953eb6e351
--- /dev/null
+++ b/test/function/samples/double-namespace-reexport/second.js
@@ -0,0 +1 @@
+export * from 'external';