type gets widened on declaration emit when inferred in destructuring context

🔎 Search Terms

declaration, widened, d.ts, destructuring

🕗 Version & Regression Information

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

⏯ Playground Link

https://www.typescriptlang.org/play?jsx=0&module=1&ts=5.1.6#code/GYVwdgxgLglg9mABMOcAUBKAXIg3gTxwEYBfPAKESsQCcBTKEGpXRQxIxE878ugDwAOcGlEQQEAZzGt8iALyIADFwXJUmANxA

💻 Code

function foo(): {y: 1} {
    return { y: 1 }
}

export const { y = 0 } = foo();

🙁 Actual behavior

y is number in d.ts files, although the language service says y is 1|0

🙂 Expected behavior

y is 1|0 in d.ts files.

Additional information about the issue

Without the = 0 assignment y properly becomes type 1 in d.ts

Use the linked TypeScript Playground and the provided destructuring example to reproduce the declaration emit. Compare the generated d.ts type for y with the language service result, then verify that the emitted type remains 1|0 when the default assignment is present while the no-default case remains 1.