Type not matched when using keyof instead of literal

[truemogician]

Bug Report

🔎 Search Terms

I've posted this problem on StackOverflow but received no comments or answers.
This problem is rather difficult to describe briefly in natural language (or maybe due to my poor English), thus I failed to find any relative questions through the search engine.

🕗 Version & Regression Information

I'm currently using TypeScript 4.4.4, earlier versions are not tested, but I suppose they'll behave the same.

💻 Code

type a = { foo: "bar" } extends { "foo" } ? true : false;
type b = { [K in keyof { "foo" }]: { foo: "bar" } extends { K } ? true : false }["foo"];

🙁 Actual behavior

a = true
b = false

🙂 Expected behavior

b should also be true

[RyanCavanaugh]

type a = { foo: "bar" } extends { "foo" } ? true : false;
type b = { [K in keyof { "foo" }]: { foo: "bar" } extends { K } ? true : false }["foo"];

The type being resolved here (annotated for additional clarity) is

{ foo: "bar" } extends { K: any } ? true : false

K in this position is a property name, not a reference to the key type. You could equally have written

type a = { foo: "bar" } extends { "foo" } ? true : false;
type b = { [K in keyof { "foo" }]: { foo: "bar" } extends { QQQ } ? true : false }["foo"];

Which is clearly correctly false

This is true as expected:

type b = { [K in keyof { "foo": any }]: ({ foo: "bar" } extends Record<K, unknown> ? true : false) }["foo"];

[truemogician]

@RyanCavanaugh Thank you!
It is me instead of TypeScript that turns out wrong lol
In fact, I'm not quite sure whether this is a bug, but since I can't get help even in StackOverflow, reporting the problem here becomes my only choice.