Incorrect type checking when object is created using spread operator

[bacher]

🔎 Search Terms

"object is created using spread operator"
"spread operator type mismatch"
"create object based on another object"
"incorrect inference when spread operator used"

🕗 Version & Regression Information

• This is the behavior in every version I tried. 5.*, 4.*, 3.*.

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=5.7.2#code/C4TwDgpgBA0hIDkCGBbaBeKByJWoB9sAjLAbgChyAzAVwDsBjYASwHs6oBzCYAZVbRwQACgCUALljxkaKAG9yUKACceNZRxxlyAX0qhIUACJJgSKJgBKEBq2UATADxCZEADRQAzsGXM6nAD4Kcls6byhWAEZJEzMLeUUoJEksAAsIABsM1iw3RKIUgHc7DPtc3WDQ8NYAJhjTc0wFJQA6Nqi8pQB6LqgAQU9PZk46NDpgL1TWGlKoKiRmDMSAbW4+AQghMQBdSQBWPJ1gnqgAFVTmTygMv2hPKZn7KAhlZTtxclqWpBbgVgBVMCQZQAYSQnggYgoJwAegB+ShfIi-AFAl5giFQ8iwhFAA

💻 Code

type KeyName = 'a' | 'b';

function getSomeKey(): KeyName {
  return 'a';
}

type Data = Record<KeyName, string>;

const o1: Data = {
  a: 'hello',
  b: 'world',
};

const o2: Data = {
  ...o1,
  // Assignment should fail
  [getSomeKey()]: 5,
};

// This line should error:
o2.a.toUpperCase();
// ^?

o2.b.toUpperCase();
// ^?

🙁 Actual behavior

This code snippet effectively puts number 5 into a field, which TS considers a string.

🙂 Expected behavior

const o2: Data = {
  ...o1,
  // Assignment should fail
  [getSomeKey()]: 5,
};

This lines should fail.

Additional information about the issue

This problem reproduced even without using of explicit Record type, example: https://www.typescriptlang.org/play/?ts=5.7.2#code/GYVwdgxgLglg9mABAcwKZQMpwLaoNKoCeAFAJQBciA5AIZWIA+1ARvQN4BQiiATuiDyS0qAbg4BfDhwgIAzlERwAjIgC8iTtxqUqAC1QAbA3CoAaLomY6A7nB4GAJmYmIasxDLDyx0uQrgATGoaFgB04crm3AD00YgAgrKyMMhguGAKsrpwII6IwDQwBhYA2miYOPhEZAC6lACs5uI+sYgAQnBQuorAiF2osqiIWTl5qDw8duQcgaE0oVBwAKoADivjAMJuqGRirQB6APxSs8wLy2ub27scB8dAA

[MartinJohns]

Duplicate of #32236.

[typescript-bot]

This issue has been marked as "Duplicate" and has seen no recent activity. It has been automatically closed for house-keeping purposes.