Incorrectly reported `TS2322` error on array items after spread

🔎 Search Terms

"array spread", "TS2322"

🕗 Version & Regression Information

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

⏯ Playground Link

https://www.typescriptlang.org/play?#code/MYewdgzgLgBAhgLhgQQE6rgTwDxgK4C2ARgKaowA+M0qAlmAOYB8MAvDANoC6A3AFChIsIkjQYc+YmRbsOAOgVwANDACMvIA

💻 Code

const a: Array<number | string> = [];
const b: Array<number> = [...a, 1];

🙁 Actual behavior

The compiler gives the following two errors, of which only one is appropriate:

~/prog/typescript ❯ tsc ./array-spread-error.ts
array-spread-error.ts:2:27 - error TS2322: Type 'string | number' is not assignable to type 'number'.
  Type 'string' is not assignable to type 'number'.

2 const b: Array<number> = [...a, 1];
                            ~~~~

array-spread-error.ts:2:33 - error TS2322: Type 'string | number' is not assignable to type 'number'.
  Type 'string' is not assignable to type 'number'.

2 const b: Array<number> = [...a, 1];
                                  ~

🙂 Expected behavior

The spread is clearly incorrect, as the original array could potentially contain strings as well, but the number literal should not be marked with the same error.

Beginne mit der verknüpften TypeScript Playground-Reproduktion und bestätige, dass der Spread und das darauf folgende numerische Literal separate TS2322-Diagnosen erzeugen. Verfolge den Checker-Pfad für Array-Literale mit Spread-Elementen und füge einen Regressionstest hinzu, der zeigt, dass nur der ungültige Spread gemeldet wird, während das numerische Literal akzeptiert wird.