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.