Accessing property with bracket notation can sometimes incorrectly return an implicit any type

[Brqqq]

Bug Report

🔎 Search Terms

implicit any, property access

🕗 Version & Regression Information

• This changed between versions 4.2.3 and 4.3.5

⏯ Playground Link

Playground link with relevant code

💻 Code

const obj = {
	A: 1,
	B: 1
};

// Ignore the implementation, it's about the inferred return type of the function, which should be "A" | "B"
const getRandomKey = () => Math.random() > 0.5 ? "A" : "B"

type Foo =  ReturnType<typeof getRandomKey> extends keyof typeof obj ? ReturnType<typeof getRandomKey> : never;

const randomKey = getRandomKey();
const casted: Foo = getRandomKey();
	
const randomKeyResult = obj[randomKey];
const castedResult = obj[casted];

🙁 Actual behavior

randomKeyResult has type 'number', but castedResult has type any

🙂 Expected behavior

Both randomKeyResult and castedResult should be type number.

If you look at the type of casted and randomKey, the types are identical: "A" | "B". Yet when using them to access a property, they behave differently. Note that in 4.2.3, this expected behavior was also the actual behavior.

[Chetan-unbounce]

looks like something changed in newer version where they are interpreting this line outputs differently
type Foo = ReturnType<typeof getRandomKey> extends keyof typeof obj ? ReturnType<typeof getRandomKey> : never;
if I change this to
type Foo = ReturnType<typeof getRandomKey>;
type of casted and randomKey both are numbers.
OR
if i type cast it at access time
type t = ReturnType1<typeof getRandomKey>; const castedResult = obj[casted as t];

[whzx5byb]

It seems that this has been fixed in 4.9.5.