fix: reset variable render names between outputs in the same generate (#6350)

When the same input bundle is generated for multiple outputs in one
`output` array, `Variable.renderBaseName` set during a chunked output's
import deconfliction (e.g. `vendor` for `_` imported from a chunk) was
left on the shared `Variable` instance. The next output's
`deconflictTopLevelVariables` then skipped that variable because of the
existing `renderBaseName`, so the function declaration was rendered as
`function vendor._(...)` — invalid JavaScript.

Reset `renderBaseName`/`renderName` for the chunk's top-level variables
at the start of `setIdentifierRenderResolutions`, before either the
exports loop or `deconflictChunk` reassigns them.

Co-authored-by: Lukas Taegert-Atkinson <lukastaegert@users.noreply.github.com>

Author: barry3406

src/Chunk.ts

@@ -1454,6 +1454,16 @@ export default class Chunk {
 			preserveModules,
 			externalLiveBindings
 		} = this.outputOptions;
+		// Reset stale render names from previous output renderings of the same
+		// module graph. Without this, variables that were renamed during a prior
+		// output's import deconfliction (e.g. given a chunk-prefixed
+		// `renderBaseName` like `vendor`) would carry that name into the next
+		// output, producing invalid identifiers such as `function vendor.foo()`.
+		for (const module of this.orderedModules) {
+			for (const variable of module.scope.variables.values()) {
+				variable.setRenderNames(null, null);
+			}
+		}
 		const syntheticExports = new Set<SyntheticNamedExportVariable>();
 		for (const exportName of this.getExportNames()) {
 			const exportVariable = this.exportsByName.get(exportName)!;

test/misc/misc.js

@@ -209,6 +209,41 @@ describe('misc', () => {
 				])
 			));
 
+	it('does not leak chunk-prefixed render names from one output into another (#6296)', async () => {
+		const bundle = await rollup.rollup({
+			input: 'main',
+			plugins: [
+				loader({
+					main: `import { _ } from 'helper';\nconsole.log(_);`,
+					helper: `export function _(target, property) { return target[property]; }`
+				})
+			]
+		});
+
+		// Generating the chunked CJS first sets `renderBaseName` on the `_`
+		// variable to the chunk name (`vendor`). Without resetting render names
+		// at the start of each output, the subsequent UMD generate would emit
+		// `function vendor._(...)`, which is invalid JavaScript.
+		const cjs = await bundle.generate({
+			format: 'cjs',
+			dir: 'dist',
+			manualChunks: id => (id === 'helper' ? 'vendor' : undefined)
+		});
+		assert.ok(
+			cjs.output.some(chunk => chunk.fileName.startsWith('vendor')),
+			'CJS output should contain a vendor chunk'
+		);
+
+		const umd = await bundle.generate({ format: 'umd', name: 'main' });
+		const umdCode = umd.output[0].code;
+		assert.ok(
+			!/function\s+vendor\./.test(umdCode),
+			`UMD output should not contain a dotted function declaration:\n${umdCode}`
+		);
+		// And the function should still parse — eval the wrapper to verify.
+		assert.doesNotThrow(() => new Function(umdCode), 'UMD output should be valid JavaScript');
+	});
+
 	it('allows passing the same object to `rollup` and `generate`', () => {
 		const options = {
 			input: 'input',