Severity: error
Category: type-check
Stage: Stage 1

Description

The TypeScript infer keyword is part of conditional types and is not valid SJS syntax.

Example

// ✗ error
type ReturnType<T> = T extends (...args: any[]) => infer R ? R : never    // SJS-E009

Fix

Annotate return types explicitly rather than inferring them from function signatures at the type level:

// ✓ correct — annotate explicitly
function fetchUser(id: number): Promise<User> { ... }

// consumer: use the known return type directly
const result: Promise<User> = fetchUser(1)

Related codes

• SJS-E008 — conditional types are also banned