Missing error when mistyped value overwrites property of spreaded generic type parameter
See original GitHub issueBug Report
🔎 Search Terms
generic argument, rest spread, false positive
🕗 Version & Regression Information
- This is the behavior in every version I tried, and I reviewed the FAQ for entries about object spread and generics
I found a few relevant issues, but none of them fully correspond to the current one:
- https://github.com/microsoft/TypeScript/issues/35858
- https://github.com/microsoft/TypeScript/issues/38469
- https://github.com/microsoft/TypeScript/issues/30129
⏯ Playground Link
Playground link with relevant code
💻 Code
interface InputProps {
value: string;
}
const getProps = (props: InputProps): InputProps => ({
...props,
value: 123, // when there is no generic type, it shows an error, as expected
});
const getPropsGenericNoSpead = <T extends InputProps>(props: T): T => {
const newProps = {...props};
newProps.value = 123; // also error, as expected
return newProps;
};
const getPropsGeneric = <T extends InputProps>(props: T): T => ({
...props,
value: 123, // no error here
});
🙁 Actual behavior
Typescript allows assigning incompatible types
🙂 Expected behavior
Typescript shows an error
Issue Analytics
- State:
- Created 3 years ago
- Reactions:6
- Comments:5
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I am also experiencing this issue and I feel quite surprised since this looks like a fairly common case when using reduce with the spread operator.
TypeScript Playground
In situations where generics are not used, the use of “Object.assign” may be a solution.
playground