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.

Comienza con la reproducción enlazada en TypeScript Playground y confirma que el spread y el literal numérico que le sigue producen diagnósticos TS2322 separados. Sigue la ruta del checker para los literales de array con elementos spread y añade una prueba de regresión que muestre que solo se informa del spread no válido, mientras que el literal numérico se acepta.