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isolatedDeclarations should not have warning for functions that have no return statements #58330

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Jack-Works opened this issue Apr 26, 2024 · 5 comments
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Declined The issue was declined as something which matches the TypeScript vision Suggestion An idea for TypeScript

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@Jack-Works
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πŸ”Ž Search Terms

isolatedDeclaration

πŸ•— Version & Regression Information

5.5.0

⏯ Playground Link

https://www.typescriptlang.org/play/?isolatedDeclarations=true&ts=5.5.0-dev.20240426#code/KYDwDg9gTgLgBAMwK4DsDGMCWEWIBQCUcA3gL5A

πŸ’» Code

export function f() {}

πŸ™ Actual behavior

Function must have an explicit return type annotation with --isolatedDeclarations. (9007)

πŸ™‚ Expected behavior

No error

Additional information about the issue

Functions with no return statements can be easily inferred as type void, so there is no need to give this warning.

@jakebailey
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jakebailey commented Apr 26, 2024

This error is intentional; a function without a return may not always be void.

declare function fail(): never;
export function f() {
	fail();
}
export const g = () => {
	fail();
}

Is:

export declare function f(): void;
export declare const g: () => never;

This can't be determined without type analysis, so is disallowed under isolatedDeclarations.

Playground Link

@RyanCavanaugh
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Correct error for function expressions, but not function declarations - declarations won't infer never

@jakebailey
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jakebailey commented Apr 26, 2024

#58331 is indiscriminate in what it affects; if we want to allow this for function declarations only, that may be possible, but it sure seems like an extra inconsistency just to avoid writing : void (and how often do people define a noop function?).

@Jack-Works
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hmm, I didn't think of never, so the function expression part is wrong. But I find it annoying to write : void for obviously clear function declarations.

@RyanCavanaugh RyanCavanaugh added Suggestion An idea for TypeScript In Discussion Not yet reached consensus Declined The issue was declined as something which matches the TypeScript vision and removed In Discussion Not yet reached consensus labels May 2, 2024
@RyanCavanaugh
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Discussed and we don't want to make it untenable to, in the future, change the rules around function declaration return type inference. For example, it's maybe preferable that

function dofail() {
  Debug.fail("oops");
}

have an inferred return type of never (as it would if written as a function expression) rather than void.

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Labels
Declined The issue was declined as something which matches the TypeScript vision Suggestion An idea for TypeScript
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