Generic readonly array of objects in function messes IntelliSense for optional props

[ftzi]

Bug Report

🔎 Search Terms

generic readonly array, readonly optional missing, function readonly, readonly array object optional...

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about readonly

⏯ Playground Link

https://www.typescriptlang.org/play?ts=4.5.0-beta#code/GYVwdgxgLglg9mABAMQDwBVEFMAeUtgAmAzogE5YCGhCANgJ6IDelAXImCALYBGWZAGkQ8A-O2JQyMMAHMAvgG0AugD4AFDnboh9dmqhaAlIgC8KxADc4MQsaYAoOffvI1CluwBMQuUuMB6f2FEGixiMAByKERiAAs4AHdEEAAHRGlEAEkwfFpaGGICQqA

💻 Code

function F<T extends readonly {a: number, b?: string}[]>(x: T, y: (t: T) => void) {
}

F([{a: 2, }]) // b doesn't show up in Intellisense after defining a

🙁 Actual behavior

No IntelliSense for optional properties in a readonly array of objects.

🙂 Expected behavior

IntelliSense for optional properties in a readonly array of objects.

I want this for my custom <Form /> React component, where I have a fields props, being it a ReadonlyArray<{id: string, props?: Props}>, and I have another prop for the component, the onSubmit function, that takes the id's const strings from the fields props to call the server with the corresponding Form data. It works, but the props property vanishes after defining the id, and it has lots of possible properties, so IntelliSense is pretty important there.

[andrewbranch]

Related:

• Incorrect inference/autocompletion on generic arrays, when values can be inferred from a defined object. #41645
• Properties in object literal key completion list aren't filtered when a prior argument supplies a mapped type key #35702
• Autocompletion broken for generic function parameter with optional properties #30507