Don't retarget dependencies if a symbol is imported multiple times with different local names

packages/core/core/src/BundleGraph.js

@@ -225,12 +225,12 @@ export default class BundleGraph {
         }
 
         if (
-          // Only perform rewriting when there is an imported symbol
+          // Only perform retargeting when there is an imported symbol
           // - If the target is side-effect-free, the symbols point to the actual target and removing
           //   the original dependency resolution is fine
           // - Otherwise, keep this dependency unchanged for its potential side effects
           node.usedSymbolsUp.size > 0 &&
-          // Only perform rewriting if the dependency only points to a single asset (e.g. CSS modules)
+          // Only perform retargeting if the dependency only points to a single asset (e.g. CSS modules)
           !hasAmbiguousSymbols &&
           // It doesn't make sense to retarget dependencies where `*` is used, because the
           // retargeting won't enable any benefits in that case (apart from potentially even more
@@ -243,7 +243,13 @@ export default class BundleGraph {
           // or
           //      (parcelRequire("...")).then((a)=>a);
           // if the reexporting asset did `export {a as b}` or `export * as a`
-          node.value.priority === Priority.sync
+          node.value.priority === Priority.sync &&
+          // For every asset, no symbol is imported multiple times (with a different local name).
+          // Don't retarget because this cannot be resolved without also changing the asset symbols
+          // (and the asset content itself).
+          [...targets].every(
+            ([, t]) => new Set([...t.values()]).size === t.size,
+          )
         ) {
           // TODO adjust sourceAssetIdNode.value.dependencies ?
           let deps = [

packages/core/integration-tests/test/integration/scope-hoisting/es6/side-effects-re-exports-rename-same/index.js

@@ -0,0 +1,3 @@
+import * as ns from "./library/a";
+
+output = [ns, ns.value1, ns.value2];

packages/core/integration-tests/test/integration/scope-hoisting/es6/side-effects-re-exports-rename-same/library/a.js

@@ -0,0 +1 @@
+export { value1, value2 } from './b.js';

packages/core/integration-tests/test/integration/scope-hoisting/es6/side-effects-re-exports-rename-same/library/b.js

@@ -0,0 +1 @@
+export { value1, value1 as value2 } from "./c";

packages/core/integration-tests/test/integration/scope-hoisting/es6/side-effects-re-exports-rename-same/library/c.js

@@ -0,0 +1 @@
+export const value1 = 123;

packages/core/integration-tests/test/integration/scope-hoisting/es6/side-effects-re-exports-rename-same/library/package.json

@@ -0,0 +1,3 @@
+{
+	"sideEffects": false
+}

packages/core/integration-tests/test/javascript.js

@@ -7079,19 +7079,6 @@ describe('javascript', function () {
         assert.deepEqual(res.output, 'bar');
       });
 
-      it('supports reexports via variable declaration (unused)', async function () {
-        let b = await bundle(
-          path.join(
-            __dirname,
-            '/integration/scope-hoisting/es6/side-effects-re-exports-rename-var-unused/index.js',
-          ),
-          options,
-        );
-
-        let res = await run(b, {}, {require: false});
-        assert.deepEqual((await res.output).foo, 'foo');
-      });
-
       it('supports named and renamed reexports of the same asset (named used)', async function () {
         let b = await bundle(
           path.join(
@@ -7126,6 +7113,32 @@ describe('javascript', function () {
         assert.deepEqual(res.output, 'bar');
       });
 
+      it('supports named and renamed reexports of the same asset (namespace used)', async function () {
+        let b = await bundle(
+          path.join(
+            __dirname,
+            '/integration/scope-hoisting/es6/side-effects-re-exports-rename-same/index.js',
+          ),
+          options,
+        );
+
+        let res = await run(b, null, {require: false});
+        assert.deepEqual(res.output, [{value1: 123, value2: 123}, 123, 123]);
+      });
+
+      it('supports reexports via variable declaration (unused)', async function () {
+        let b = await bundle(
+          path.join(
+            __dirname,
+            '/integration/scope-hoisting/es6/side-effects-re-exports-rename-var-unused/index.js',
+          ),
+          options,
+        );
+
+        let res = await run(b, {}, {require: false});
+        assert.deepEqual((await res.output).foo, 'foo');
+      });
+
       it('supports named and namespace exports of the same asset (named used)', async function () {
         let b = await bundle(
           path.join(