Impossible to annotate parameter properties in an isolatedDeclarations compatible way

[blickly]

🔎 Search Terms

isolatedDeclarations, parameter properties, implicit undefined

🕗 Version & Regression Information

• Present since isolatedDeclarations was added in TS5.5

⏯ Playground Link

https://www.typescriptlang.org/play/?downlevelIteration=true&importHelpers=true&target=99&module=1&isolatedDeclarations=true&noCheck=true&exactOptionalPropertyTypes=true&ssl=3&ssc=2&pln=1&pc=1#code/KYDwDg9gTgLgBAYwDYEMDOa4CEVTgbwCg4TEIA7NGKAVwRmgAowoBLANxRmDhAH4AXHACCUKCgCecAD5wa5ACbAAZq3LAFASgIBfQjqA

💻 Code

export class Bar {
    constructor(private x?: Array | undefined) {}
}

🙁 Actual behavior

Error:

Declaration emit for this parameter requires implicitly adding undefined to it's type. This is not supported with --isolatedDeclarations.

🙂 Expected behavior

Should not give an error since the undefined is already explicit.

Additional information about the issue

No response

[jcalz]

Why are you writing Array without its type argument like Array<any> or Array<number>? Isn't that the source of the problem? Or is it just a typo?

[Andarist]

That is the issue but I'd consider the raised error to be a bug, at the very least it's quite confusing here

[blickly]

Oops, you are right. I oversimplified my original example to get something unrealistic. My original repro case was actually:

import {Foo} from 'other';

export class Bar {
    constructor(private x?: Foo | undefined) {}
}

https://www.typescriptlang.org/play/?downlevelIteration=true&importHelpers=true&target=99&module=1&isolatedDeclarations=true&noCheck=true&exactOptionalPropertyTypes=true#code/JYWwDg9gTgLgBAbwGIQgXzgMyhEcDkEMAFgKZT4DcAUNaQB6SxwDGANgIYDOXcAQhyiJqcUawgA7LjCgBXFjGgAKMFGAA3DjFJx6AfgBccFBDgAfOLIkATUpmATS1gJSI01NEA

But I think that the fix will work either way.

[Andarist]

Yeah, I have added a test case similar to it in my PR:

export function test2(x?: Unresolved | undefined): void {}