Optional discriminated union's callback parameter type is not inferred

discriminated union

Code

type T1 = {
        as?: 'button',
        onClick?: (el: number) => void
} 

type T2 = {
        as: 'a',
        onClick?: (el: string) => void
}

type T = T1 | T2;

// onClick first parameter type is inferred according to T1 (number)
const myT1_1: T = {
        as: undefined,
        onClick: _ev => {}
}

// onClick first parameter type is inferred according to T1 (number)
const myT1_2: T = {
        as: 'button',
        onClick: _ev => {}
}

// onClick first parameter type is inferred according to T2 (string)
const myT2_1: T = {
        as: 'a',
        onClick: _ev => {}
}

// onClick first parameter type is not inferred (any)
const myT1_3: T = {
        onClick: _ev => {}
}

Expected behavior:
onClick _ev parameter of myT1_3 is inferred to be a number

Actual behavior:
onClick _ev parameter of myT1_3 is any

Playground Link:
Playground Link

If the callback in T1 and T2 is replaced with a primitive member then myT1_3 is inferred correctly. Playground Link

This appears to be a duplicate of #41759

The parameter seems to be correctly inferred in the latest version of typescript, can this be closed as fixed?

Confirmed fixed 4.2 -> 4.3

Ryan Cavanaugh (@RyanCavanaugh)

Ryan Cavanaugh (@RyanCavanaugh) Still exist in the last version..

https://www.typescriptlang.org/play?ts=4.5.0-beta#code/C4TwDgpgBAglC8UDeAoK6qkgfgFxQHIYCAaNDAQ3wAoBjfJKAE3wDsBXAWwCMIAnKAF8AlAgB8UAG4B7AJZMA3CkEoUWaACEEycunX4CG0rqhUodBszZdefElHpQAzsD6zWAcyGj4EmfKUVVXVYDQBhbTgAHygtJRRJCgEzGHCAbQBdKBiAJQhaaT4mAB4XN097VLDMiUQ0k1QMJtMaMCSKTicfCUbmvpMmlUGUDKA

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Optional discriminated union's callback parameter type is not inferred #35769

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Optional discriminated union's callback parameter type is not inferred #35769

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wvanvugt-speedline commented on Feb 5, 2021

IanVS commented on Jun 4, 2021

RyanCavanaugh commented on Jun 11, 2021

wzono commented on Nov 18, 2021

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