[Bug]: duplicated default import

[nstepien]

Reproduction link or steps

Repo branch: Comcast/react-data-grid#3578

• git clone https://github.com/adazzle/react-data-grid.git
• git checkout rolldown
• npm i
• npm run build
• open lib/bundle.js
• notice that that the default export of clsx is imported multiple times with different identifiers

  import clsx, { default as clsx$1, default as clsx$2, default as clsx$3, default as clsx$4, default as clsx$5, default as clsx$6, default as clsx$7 } from "clsx";

What is expected?

I'd expect the following import to not result in multiple imports.

import clsx from "clsx";

What is actually happening?

The clsx default export is imported under multiple identifiers.

System Info

System:
    OS: Windows 11 10.0.26100
    CPU: (64) x64 AMD Ryzen Threadripper 3970X 32-Core Processor
    Memory: 11.11 GB / 31.88 GB
  Binaries:
    Node: 23.5.0 - C:\Program Files\nodejs\node.EXE
    npm: 11.0.0 - C:\Program Files\nodejs\npm.CMD
  Browsers:
    Edge: Chromium (131.0.2903.99)
    Internet Explorer: 11.0.26100.1882
  npmPackages:
    rolldown: ^0.15.1 => 0.15.1

Any additional comments?

The CJS output (lib/bundle.cjs) does not have this issue.
Rollup does not have this issue either.

[hi-ogawa]

I made a minimal-ish repro https://stackblitz.com/edit/github-ugpzvon2?file=src%2Fentry.js

Esbuild also doesn't dedupe same external imports (though in a different way) esbuild try and there's an issue about it evanw/esbuild#475

[nstepien]

Other external imports don't exhibit this behavior in my build, that's odd. 🤔

import { createContext, forwardRef, memo, useCallback, useContext, useEffect, useId, useImperativeHandle, useLayoutEffect, useMemo, useRef, useState } from "react";
import { flushSync } from "react-dom";
import clsx, { default as clsx$1, default as clsx$2, default as clsx$3, default as clsx$4, default as clsx$5, default as clsx$6, default as clsx$7 } from "clsx";
import { Fragment, jsx, jsxs } from "react/jsx-runtime";

Maybe it's only an issue with default imports?

[hi-ogawa]

Indeed, this seems to only happen for default import. I updated the repro above now output looks like this:

import externalDefault, { externalNamed, default as externalDefault$1 } from "external";

//#region src/dep.js
var dep_default = "dep";
console.log({
	externalDefault: externalDefault$1,
	externalNamed
});

//#endregion
//#region src/entry.js
console.log({
	externalDefault,
	externalNamed,
	dep: dep_default
});

//#endregion

[hyf0]

Seems default doesn't get merged on purpose @IWANABETHATGUY cc

rolldown/crates/rolldown/src/stages/link_stage/bind_imports_and_exports.rs

Lines 392 to 400 in 80d522f

	if name.as_str() != "default" {
	self
	.external_import_binding_merger
	.entry(rec.resolved_module)
	.or_default()
	.entry(name.inner().clone())
	.or_default()
	.insert(*imported_as_ref);
	}