Type checking is ignored with spread operator, especially with truthy expression.

[dimak-dev]

🔎 Search Terms

spread operator with expression

🕗 Version & Regression Information

• Tested with www.typescriptlang.org with versions from 3.3.3 to nightly (v5.4.0-dev.20240131)

⏯ Playground Link

No response

💻 Code

type Type = {
 property: string,
}

let typedVar1: Type = {
 property: 'string',
 anotherProperty: 'foo', // TS-2353: Object literal may only specify known properties, and 'anotherProperty' does not exist in type 'Type'.
}

let typedVar2: Type = {
 property: 'string',
 ...({anotherProperty: 'bar'}), // No error
}

let typedVar3: Type = {
 property: 'string',
 anotherProperty: 'foo', // TS-2783: 'anotherProperty' is specified more than once, so this usage will be overwritten.
 ...({anotherProperty: 'bar'}),
}

let typedVar4: Type = {
 property: 'string',
 anotherProperty: 'foo', // No error, total ingoring
 ...(1 == 1 && {anotherProperty: 'bar'}),
}

console.log(typedVar2); // {"property": "string", "anotherProperty": "bar"} 
console.log(typedVar2.anotherProperty); // TS-2339 : Property 'anotherProperty' does not exist on type 'Type'.
console.log(typedVar4); // {"property": "string", "anotherProperty": "bar"} 
console.log(typedVar4.anotherProperty); // TS-2339 : Property 'anotherProperty' does not exist on type 'Type'.

🙁 Actual behavior

1. TS-2353: Object literal may only specify known properties, and 'anotherProperty' does not exist in type 'Type'
2. No error
3. TS-2783: 'anotherProperty' is specified more than once, so this usage will be overwritten.
4. No error

🙂 Expected behavior

1. TS-2353: Object literal may only specify known properties, and 'anotherProperty' does not exist in type 'Type'
2. TS-2353: Object literal may only specify known properties, and 'anotherProperty' does not exist in type 'Type'
3. TS-2353 + TS-2783
4. TS-2353 + TS-2783

Additional information about the issue

No response

[MartinJohns]

Duplicate of #39998. Type checking is not ignored and works, just excess property checks not.

[fatcerberus]

le sigh... this error message really needs to be softened to make it more obvious EPC isn't a type check.
Count this as another vote for something like #55152 (comment)

[typescript-bot]

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