Boolean narrowed to true only when generic type is explicitly provided while it shouldn't

🔎 Search Terms

specify type narrow union

🕗 Version & Regression Information

All versions I checked and nothing in FAQ that seems related

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/LAKA9GCqDOCmAEAXAFggbgQwE4EsMDsBjBA-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-PqQILycKy7zPabZaBKRaQGs0Vysd1hVbCcTYkl4P6AErDgDyw4NFLpmqZTF1F0rZMNuPxsHNoXZ5F07CoSDXINgiK4ghOCA9Eq9+DdsgLnCG9sdsGd8Fd8DdvZ9IHZAbzocQ4aRtGOCxuwCZJrghCpumGbzlgJxnAQJjZNmGQ6LAgbBv+ABMhbYMWFKljyXSVtWJyzKKfgNjKBwtpubZ1OimISgRNbNNRZqgO23argSRIkkOYD6FgwzQL6YC-lhYYRlG1QgXGqDwIm+DJlBaZYJmcEIfBSG2K6Oi9q+XAcahxwYX+2gAMx4VgrGvhRnwLKR1a1sRYqXo2tEKvR3GdhK2K8SQxkeQQ-EDoJwmieyABCIX4NEvbxBgBjQAwkViSAQA

💻 Code

// Use the variance annotation to force this type to be invariant, even though it would otherwise be covariant
type Invariant<in out T> = () => T;

const foo = <T extends object>(obj: T): Invariant<{[P in keyof T]: Invariant<T[P]>}> => null!;
const bar = <T extends {[P in keyof T]: Invariant<any>}>(w: T): T => null!;

const inferred = bar({a: foo({b: true})}); // true is boolean as expected

// Explicitly specify the generic param
const explicit = bar<{
    a: Invariant<{
        b: Invariant<boolean>;
    }>
}>({a: foo({b: true})}); // narrowed to true instead of boolean and errors

🙁 Actual behavior

Narrows to true

🙂 Expected behavior

Should stay boolean

Additional information about the issue

Doing as boolean works...

Start with the linked TypeScript Playground repro and confirm the difference between inferred and explicitly supplied generic types, focusing on the boolean literal narrowing through the invariant mapped types. Trace the type-checking behavior that produces true instead of boolean, then add a regression test showing that the explicit call preserves boolean without requiring as boolean.