Turbopack Error: esmExternals = "loose" is not supported

[shresthamishra76]

Turbopack version: v15.4.2-1-ga5b73c3fd
Next.js version: 0.0.0

Error message:

esmExternals = "loose" is not supported

Debug info:
- Execution of get_entrypoints_with_issues_operation failed
- Execution of EntrypointsOperation::new failed
- Execution of Project::entrypoints failed
- Execution of Project::middleware_endpoint failed
- Execution of *MiddlewareEndpoint::new failed
- Execution of Project::middleware_context failed
- Execution of *parse_config_from_source failed
- Execution of *ProcessResult::module failed
- Execution of *AssetContext::process failed
- Execution of Project::edge_middleware_context failed
- Execution of AppProject::edge_ecmascript_client_reference_transition failed
- Execution of *NextEcmascriptClientReferenceTransition::new failed
- Execution of AppProject::edge_ssr_transition failed
- Execution of *FullContextTransition::new failed
- Execution of AppProject::edge_ssr_module_context failed
- Execution of AppProject::edge_shared_transition failed
- Execution of *FullContextTransition::new failed
- Execution of AppProject::edge_shared_module_context failed
- Execution of *ModuleAssetContext::new failed
- Execution of get_server_module_options_context failed
- Execution of NextConfig::import_externals failed
- esmExternals = "loose" is not supported

[grilomatheus]

You’re hitting this because Turbopack doesn’t support esmExternals: "loose". That flag was a Webpack-mode escape hatch and isn’t implemented in Turbopack.

Fixes:

1. Remove it from your config (recommended):

// next.config.(js|ts)
export default {
  // experimental: { esmExternals: "loose" }, // ❌ remove
}

If you added anything under experimental.turbo before, note it’s deprecated—use the top-level turbopack key only for things Turbopack actually supports.

2. If you rely on “loose” behavior, run with Webpack instead of Turbopack for now:

• Dev: start without Turbopack (e.g. next dev, not next dev --turbopack)
• Keep esmExternals: "loose" only when using Webpack.

That should unblock the build. If you share a repro, happy to confirm which dep is requiring “loose” and whether there’s a Turbopack-friendly alternative.