ThisType is invalid when using object spread on generic object

Bug Report

🔎 Search Terms

ThisType Object Spread Generic

🕗 Version & Regression Information

• I was unable to test this on prior versions because I was not using this feature previously

⏯ Playground Link

Playground link with relevant code

💻 Code

function createObject<D extends {}>(def: D & ThisType<D>) { /* some code */ }

const namableObject = { name: '' };
// ThisType will be wrongly typed when using object spread
const spreadObject = createObject({
  ...namableObject,
  get thisName() {
    return this.name; // <-- Property 'name' does not exists on type '{}'
  },
});
// Correctly typed otherwise
const fullObject = createObject({
  name: '',
  get thisName() {
    return this.name;
  },
});

🙁 Actual behavior

The generic type is broken when the given object value contains a spread object.

🙂 Expected behavior

The generic type should contain the spreaded object properties as those are finally included into the result object.

Comment

This may be related to #26412 and other issues like this one but I didn't found a workarround to get a ThisType correctly typed.

Start with the linked TypeScript Playground reproduction and compare the spread and non-spread calls to createObject. Trace how generic inference handles the spread object and ThisType context; done means the getter in spreadObject recognizes the name property without regressing the existing fullObject case.