Describe the bug

Currently in Vite 8 rolldown's topLevelVar options is true by default.

Variables defined with var are not "inlined" during dead code elimination, which breaks dead code elimination.

Reproduction

https://repl.rolldown.rs/#eNptUcFuwjAM/RUrF4pUFQG3TjvtuvNOuaStC9lCUjUOY6r677NTxhiaVDWx/Z79/DKpXtWTsr7DS0VR7l7Vv3GpWglPQxgJJiCMBDP0YzjBqto426y0174NPgaHlQuHQiDFeq09c1HVNCacSzUG57rw6SuG9vZwN+qfysPQDnvr8SWXb8N/aHk+XjKUgSa5fN4IxaQ9QEg0JKohBwAUhlc8o3szYw2iUNJzKX/rM3AZXp2QTJVTJWw2QEeE3jqMENFhS9hB85WzTSIKHvhD0x6BTCPNmBIGsuyO9rNYwk4Mpv0wB6zeY+D1Fw/+5Jbts1KtOhyQ38K3FqNWvMDMnZZGbP6djddoITskSJHVPUNvXMSnm0V98q0IknKxFj80XZHiAwO5+yN2edIFbHsohLCGESmNHra7PbM0XcP9bitN1MwKzyLFCFvN30sw0+k=

Steps to reproduce

// lib.ts
let used = false;
export function use() {
	used = true;
}
export function test() {
	if (used) return 123;
	return 321;
}

// index.ts
import { test } from './lib'

console.log(test())

expected output (with topLevelVar: false)

function test() {
	return 321;
}
//#endregion
//#region index.ts
console.log(test());
//#endregion

actual Vite 8 output (topLevelVar: true)

//#region lib.ts
var used = false;
function test() {
	if (used) return 123;
	return 321;
}
//#endregion
//#region index.ts
console.log(test());
//#endregion

Rolldown Repl example with topLevelVar: true

Rolldown Repl example with topLevelVar: false

System Info

Rolldown Repl

Used Package Manager

npm

Logs

No response

Validations

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• Read the Contributing Guidelines.
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• The provided reproduction is a minimal reproducible example of the bug.