"Unreachable code detected (7027)" false positive in 3.7

[iyegoroff]

TypeScript Version: 3.7-beta, 3.7.1-rc, Nightly

Search Terms: declare never unreachable 7027

Code

declare function foo(): never

function bar() {
    foo()

    return 1
}

Expected behavior: no errors

Actual behavior: received error: "Unreachable code detected.(7027)"

Playground Link: https://www.typescriptlang.org/play/index.html?ts=3.8.0-dev.20191101#code/PTAEDMFcDsGMBcCWB7aFnIBQEpQG8AoEUEkgJwFN5Iy0BGUAQwGdRoKA3CsosAXwIEAJhVgAbRpQgwEKNOAw4AXG07dBUOElSgARpJz4CpdFmyCTlarVB0CAgkA

Related Issues: -

[MartinJohns]

I would say this works as intended. The function foo declares that it will never return (by having never as the return-type). So the compiler correctly assumes that any code that comes after calling this method won't ever run.

Why do you consider this a false positive?

Related issue: #28859

[fatcerberus]

https://devblogs.microsoft.com/typescript/announcing-typescript-3-7-rc/#better-support-for-never-returning-functions

[iyegoroff]

@MartinJohns , @fatcerberus , thanks for the answers!

Why do you consider this a false positive?

Because it wasn't an error in 3.6 and https://www.typescriptlang.org/play/index.html?ts=3.8.0-dev.20191101&ssl=3&ssc=2&pln=1&pc=1#code/GYVwdgxgLglg9mABMOcAUBKRBvAUIgxAJwFMoQikBGRAQwGdEwSA3Eo3AX111ElgSIARrSKYc+QinQYehYmQrUuPIA also doesn't produce any errors