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

使用链接的 TypeScript Playground 和提供的 destructuring 示例来复现 declaration emit。将为 y 生成的 d.ts 类型与 language service 的结果进行比较，然后验证存在默认赋值时 emit 的类型仍为 1|0，而无默认值的情况仍为 1。