`@deprecated` nested namespace handling is buggy

🔎 Search Terms

deprecated nested namespace

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/FAegVGAEACAmCmAHATvAxgQwC71pMIwAdhgLbwDOiGa8kAYgPaMCMAdAEIbKQDewkSPAAeiRsiyQ0jIhUnDIAXkgsA3MAC+wYmUrVaDZuy4AvPgKGjxk6bPlKV6rcCatO3NsPWvjGE5-VtUBAQoJ1yKho6VwAmdzN+QRExCSkZOUgFZTVNbXAoOCRUTBw8AnC9KMNGOK4eRMsUm3T7bKcg2PdkAJdmWr8e7SA

💻 Code

/** @deprecated */
namespace Foo1.Bar {
  export const x = 1;
}

namespace Foo1.Baz {
  export const x = 1;
}

Foo1.Bar.x;
Foo1.Baz.x;

namespace Foo2.Baz {
  export const x = 1;
}

/** @deprecated */
namespace Foo2.Bar {
  export const x = 1;
}


Foo2.Bar.x;
Foo2.Baz.x;

🙁 Actual behavior

Usages of Foo1 are stricken through

But usages of Foo2 are not stricken through

Yet intellisense shows the tag in the hover for Foo2

🙂 Expected behavior

Either both Foo1 and Foo2 should be treated as deprecated, or neither should and instead the Bar in Foo1.Bar and Foo2.Bar should be treated as deprecated.

Additional information about the issue

@typescript-eslint recently released a new lint rule no-deprecated which reports a lint error whenever you use a thing marked with @deprecated.

A user mentioned to us that the rule reports incorrectly in certain cases (https://github.com/typescript-eslint/typescript-eslint/issues/9902).

Specifically in a case like this https://github.com/DefinitelyTyped/DefinitelyTyped/blob/d1c172bdcfd4508405f4b233e11ccd7d8743f763/types/chrome/index.d.ts#L8553-L8556

We did some investigation and found that things can be pretty ambiguous when nested namespace declarations are marked @deprecated like this and TS itself struggles with it.

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It's worth noting that the above behaviour is consistent between nested namespace shorthand (namespace Foo.Bar) and the non-shorthand style

Note you see similar behaviour for many declaration-merged things where TS's handling only makrs something as deprecated if the first definition is marked as deprecated, eg Enums.

But there are also cases where TS gets it right, eg Interfaces

Then there are weird cases like type/value shadowing where I'm not sure if TS is right or wrong -- depends on what you expect I guess.

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I would love to see some clarification on what you guys think is the correct behaviour so that we can follow-suit!