Type narrowed to `never`, incorrectly

[ljharb]

TypeScript Version: latest

Search Terms: n/a

Code

function f(a?: {}) {
 if (!a) {
 // filters out falsy values:
 // - `null`
 // - `undefined`
 // - `false`
 // - `NaN`
 // - `0` / `-0`
 // - `''`
 return {};
 }

 // here, the type of `a` has been narrowed from "optional {}"
 // to just "{} minus `object`" (object-coercible, ie, anything but null/undefined, but not `object`)
 // effectively, this is `string | number | symbol | boolean | Function`

 if (typeof a !== 'object') {
 // `a` here could be the following values:
 // - a function
 // - `true``
 // - a non-zero non-`NaN`` number
 // - a non-empty string
 // - a symbol
 return a; // however, the type inferred here is `never`
 }

 // here, `a` has a verifiably certain type of `object`.
 // because of the type guard above.
 return a; // however, the type is reported as `{}` 
}

Expected behavior: The type of a inside the if block will be either {}, or better, string | number | symbol | boolean | Function.

Actual behavior: The type of a inside the if block is never, which is flat out incorrect.

Playground Link: link

Related Issues: not sure how to search for it

[DanielRosenwasser]

It's kind of funny, but we were actually talking about #18196 right as you were opening this issue.

But filing this as a duplicate of #18196

[ljharb]

This may be addressed by #27157; it can be closed or left open til the next release, as you like.

[typescript-bot]

This issue has been marked as a 'Duplicate' and has seen no recent activity. It has been automatically closed for house-keeping purposes.