[ID-Prep] Type of variable is widened in declaration with !strictNullChecks

The [ID-prep] set of issues aligns Declaration Emit with the forthcoming Isolated Declarations feature.

🔎 Search Terms

const declaration widen

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

Playground Link

💻 Code

declare function f3<T>(a: T, b: T): T;
const x3 = f3("abc", "def");  // "abc" | "def"

🙁 Actual behavior

x3 is emitted as declare const x3: string; in declaration files but it's actually "abc" | "def" in source

🙂 Expected behavior

x3 is emitted as declare const x3: "abc" | "def"

Additional information about the issue

No response

Commencez par la reproduction liée dans TypeScript Playground et le comportement d’émission des déclarations décrit dans l’issue. Suivez comment l’union littérale inférée de l’appel générique devient le type de déclaration émis ; c’est terminé lorsque la déclaration conserve "abc" | "def" au lieu de string.