Unsafe type Inference with spread

[changchanghwang]

🔎 Search Terms

unsafe type with spread, spread, optional type, type inference

🕗 Version & Regression Information

I think all versions

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/MYGwhgzhAECCBCBhaBvAUNaBLAJgLmggBcAnLAOwHMBuDaMA4sq2u4Ae3KYFdgj2SACjAlKEAinqNSFStAC+ASlR1MRABZYIAOlzQAvNABEARiO1MazTrAH6omxYVo6AdywbhDifQD805jklFUtoDi4iegAjYDtyAFNXOCRBdFDMbUyNLQAaVUsGezFtMDzQpSdMMBjdHDtsnVxK6BJ4om4ScmjgJ3k0PrRw4m64xOTEVIYAcnV4kBB2aFcBEBwppUHOCHYQeO0FykEjVohuECI8Ixzu7XdPFCUSxSA

💻 Code

class ABC {
  id: string;
  a: string;

  constructor(args: { a: string }) {
    this.id = "1";
    this.a = args.a;
  }

  with(args: { a?: string }) {
    const abc = new ABC({
      ...this,
      a: args.a,
    });
    abc.id = this.id;
    return abc;
  }
}

🙁 Actual behavior

when I use with method without arguements like below

const abc = new ABC({ a: 'hello world' });
const newAbc = abc.with({});

newAbc.a is undefined.
constructor want a is required but with give constructor undefined.
I think it's not expected working.

🙂 Expected behavior

It should be caught by compiler. because It's not developer expected working!

Additional information about the issue

No response

[jcalz]

Note: not a TS team member.

Duplicate #60623, #50559, #10727. this is effectively generic, generic spread is modeled by intersections, which don't adequately capture how properties can be overwritten.

The title and search terms do not adequately summarize or reflect the issue you're facing. If this were not a duplicate, I'd suggest you edit to address it.

[changchanghwang]

Note: not a TS team member.

Duplicate #60623, #50559, #10727. this is effectively generic, generic spread is modeled by intersections, which don't adequately capture how properties can be overwritten.

The title and search terms do not adequately summarize or reflect the issue you're facing. If this were not a duplicate, I'd suggest you edit to address it.

sorry, I'm not good at english🥲
is it related with generic?

In this manner, if it becomes this & { a: string | undefined; }, then a can ultimately be undefined, so I think it should be inferred as optional, regardless of what this is.

[MartinJohns]

I think it should be inferred as optional

But it's not optional, it's always provided. Optional has different semantics (defined or not defined), which matters with exactOptionalPropertyTypes enabled.

[changchanghwang]

I think it should be inferred as optional

But it's not optional, it's always provided. Optional has different semantics (defined or not defined), which matters with exactOptionalPropertyTypes enabled.

oh my mistake.
a always provided. (even a is undefined) but It should be inferred as string | undefined.
constructor need string a, but with method can provide undefined
It's weird unsafe type inference

[changchanghwang]

When TypeScript uses the spread operator, excess property checks can be unintentionally disabled, resulting in unsafe type inference.
It seems like we need an option to �fix this issue.
Could we handle it similarly to how object literals are type-checked?