Type narrowing not work with inferred function arguments

[weijarz]

Bug Report

🔎 Search Terms

type narrow argument

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

https://www.typescriptlang.org/play?ts=4.4.2#code/CYUwxgNghgTiAEAzArgOzAFwJYHtXwHcYoAHAMTTAApEAueKzAD3oGEMmBKeAXgD54ANxxZgnesNEAoUJFgIU6bHnhwAjsixwAyhhhUAzvQN6sqAObihI4FKlmMIGIihgE7JvADeU+PAwAFjA4BIYYUBjIRvCoyAC2AEZOVqgggk4A3FIAvnZQBgCe6EiUyviIAEyMHGwc3D5+ECAY8NEmMGbm8AA+SFAQBgg88GigiGYgwPD506gFvvBYiAwAhAbczAB0gcGhAIwADAecC+qaOnqGJ7lSRKQU6FT5RWAlSrj41SzwHvULTS02qYLD0+gMhiNUGMJlMZlA5gslqt1vAtjsQlRDsdTiANFoQLp9OscidbsRyJQnoViopMB8GMw-o1mq1jMCur0XODeJDoalYQZZvM-EiqGsNhxtkEMViTn4zvjCVd4AB6FXwAA8AFotfAAAYGPWLQXtTqgrmDElSIA

💻 Code

declare function wrapFunc(f: (ctx: Ctx) => void): void
declare function requireStr(s: string): void

interface Ctx {
  throw(status: number): never;
}

async function f2(ctx: Ctx) {
  let s: string | false = undefined as any
  if (!s) ctx.throw(100)
  requireStr(s)
}

wrapFunc(async function (ctx: Ctx) {
  let s: string | false = undefined as any
  if (!s) ctx.throw(100)
  requireStr(s)
})

wrapFunc(async function (ctx) {
  let s: string | false = undefined as any
  if (!s) ctx.throw(100)
  requireStr(s) // <-- Compile Error!  here `s` is string | false
})

[andrewbranch]

Documented as a limitation of #32695. #33622 considered calling this out as an error, but ultimately decided against it for never-returning functions. You can choose between the type annotation and simply writing return ctx.throw(100).