remanso/docs/bugs/rolldown-while-in-globalThis.md

Rolldown minifier drops while( keyword — invalid syntax in Safari

Status: To be filed Workaround applied: build: { minify: "esbuild" } in vite.config.mts

Summary

Rolldown's minifier drops the while(/for(; keyword when a while (x in globalThis) loop is bundled alongside other module-level variable declarations. The resulting output is a syntax error that crashes Safari.

Target repositories

• https://github.com/rolldown/rolldown/issues
• https://github.com/oxc-project/oxc/issues (underlying minifier)

Environment

Package	Version
vite	8.0.1
rolldown	1.0.0-rc.10
@oxc-project/types	0.120.0
Triggered by	@ark/schema 0.56.0 / arktype 2.1.29

Source

File: node_modules/@ark/schema/out/shared/registry.js

let _registryName = "$ark";
let suffix = 2;
while (_registryName in globalThis)
    _registryName = `$ark${suffix++}`;
export const registryName = _registryName;

Actual minified output

un=Pe(`implementedTraits`),dn=`$ark`,fn=2;dn in globalThis;)dn=`$ark${fn++}`;var pn=dn;

The while( keyword is missing. The orphaned ) is a syntax error.

Expected output

var dn=`$ark`,fn=2;for(;dn in globalThis;)dn=`$ark${fn++}`;var pn=dn;

Impact

Safari throws: SyntaxError: Unexpected keyword 'in'. Expected a ';' following a return statement. Chrome and Firefox appear to tolerate the malformed output.

Reproduction attempts

Direct Rolldown calls (even with the full arktype + @better-fetch/fetch bundle) do not reproduce the bug. It only manifests through Vite's full production build pipeline. This strongly suggests the issue is in the interaction between Vite's module preprocessing (dependency pre-bundling, plugin transforms, scope-flattening of ESM modules) and Rolldown's minifier sequences optimization pass.

Hypothesis: Vite's pipeline produces a flattened scope where multiple var declarations from different original modules are consecutive. When the sequences optimizer then tries to fold those var declarations into the for loop init, it incorrectly drops the for(var prefix when the loop condition contains the in operator.

Notes

• Related closed issue: rolldown/rolldown#8146 — "Minifier incorrectly merges statements into for-in expression via comma operator"
• To reproduce: run pnpm build in this project without build.minify: "esbuild" — the broken chunk is getAuthor-*.js

Workaround

Add to vite.config.mts:

build: {
  minify: "esbuild",
},

esbuild correctly outputs for(;Dt in globalThis;)Dt=\$ark${za++}``.