TS2366: Function lacks ending return statement in function with unknown return type with implicit return on some code paths, despite noImplicitReturns turned off

Bug Report

🔎 Search Terms

lacks ending

🕗 Version & Regression Information

This changed between versions 5.0.2 and 5.1.0-dev.20230323

I believe this caused it.

⏯ Playground Link

https://www.typescriptlang.org/play?noImplicitReturns=false&ts=5.1.0-dev.20230323#code/GYVwdgxgLglg9mABFApgZygCgJQC5HgDWYcA7kgN4CwAUAJAzCKYCyAhlABYB0ATm2AAmcALY5EAPkQAGbgFZsiXiigheSKLxAoA3LQC+QA

💻 Code

function test(): unknown {
	if (Math.random() > 0.5) return true;
}

🙁 Actual behavior

> tsc --noEmit

index.ts:1:18 - error TS2366: Function lacks ending return statement and return type does not include 'undefined'.

1 function test(): unknown {
                   ~~~~~~~

🙂 Expected behavior

No error, if the function return type is unknown I'd expect that to allow implicit return of undefined.

This changed between versions 5.0.2 and 5.1.0-dev.20230323

The error message changed, but this is an error in 5.0.2 and earlier too:

Uh, the playground link had noImplicitReturns turned on. If you turn it off, it only becomes an error after 5.0.2. I'll update the link

What do you know, this actually broke some real-world code already. 😄
#53474 (comment)

Believe it or not, I found this in real-world code :D

I think the simplest fix would just be to check for TypeFlags.Unknown - alternatively, we restore the isTypeAssignableTo(undefinedType, type) check.

Let's make sure that we test strictNullChecks on/off with other top-y types.

// @strictNullChecks: true,false

function foo(): unknown {
    if (Math.random()) return true;

    // implicit return
}

function bar(): {} {
    if (Math.random()) return true;

    // implicit return
}

function baz(): Record<string, any> {
    // implicit return
}

function blah(): any {
    // implicit return
}

Navigation Menu

Repository navigation

TS2366: Function lacks ending return statement in function with `unknown` return type with implicit return on some code paths, despite `noImplicitReturns` turned off #53473

Bug Report

🔎 Search Terms

🕗 Version & Regression Information

⏯ Playground Link

💻 Code

🙁 Actual behavior

🙂 Expected behavior

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

TS2366: Function lacks ending return statement in function with unknown return type with implicit return on some code paths, despite noImplicitReturns turned off #53473

Description

Bug Report

🔎 Search Terms

🕗 Version & Regression Information

⏯ Playground Link

💻 Code

🙁 Actual behavior

🙂 Expected behavior

Activity

fatcerberus commented on Mar 23, 2023

AlCalzone commented on Mar 23, 2023

fatcerberus commented on Mar 23, 2023

AlCalzone commented on Mar 23, 2023

DanielRosenwasser commented on Mar 23, 2023

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions

TS2366: Function lacks ending return statement in function with `unknown` return type with implicit return on some code paths, despite `noImplicitReturns` turned off #53473