Too wide diagnostic with array spread

🔎 Search Terms

array spread, diagnostics

🕗 Version & Regression Information

• This is the behavior in every version I tried and I have reviewed the FAQ

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.4.4#code/C4TwDgpgBAggRgYygXigIgIZqgH3XbPNBNAbgChyEB7AOwGdgoMAnFjEARgC5ZEBtALooo-TGgA0+NIIpU6jZmw4AmXvARCR-clD1QAdEdbsuE3fvFSLetAXP70AE0nlBQA

💻 Code

type Abc = "a" | "b" | "c";

const array1: Abc[] = ["a", "b"];

const array2: Abc[] = [
    ...array1,
    "a", 
    "b",
    "d",
]

🙁 Actual behavior

The whole contents of array2 is highlighted in red.

🙂 Expected behavior

Only the "d" should be highlighted in red, as it is the only incorrect part of array2. Note that if we remove the spread ...array1, then it works as expected.

Additional information about the issue

With more complicated types/data, this bug can make it pretty hard to diagnose where the problem is.

Start with the linked TypeScript Playground reproduction and the array-spread example in the issue. Trace how diagnostics are produced for the array literal, then verify that only the "d" element is highlighted while the spread and valid elements are not.