Incorrect typing when a type uses Omit and inherits properties from a grandparent interface

[afonsof]

I am experiencing an incorrect typing issue in TypeScript when using Omit on an interface that inherits properties from a grandparent interface.

Steps to Reproduce

• Define a grandparent interface with a optional property.
• Create a parent interface that extends the grandparent interface.
• Create a new type using Omit to exclude a property from the parent interface.
• Generate the schema using the Child type

Code Example

interface Grandparent {
  a?: string
}

interface Parent extends Grandparent {
  b: string
}

export type Child = Omit<Parent, 'b'>

Generated output

{
  "definitions": {
    "Child": {
      "properties": {
        "a": {}
      },
      "required": [
        "a"
      ],
    }
  }
}

Expected Behavior

The grandparent property should be correctly typed and not be required

{
  "definitions": {
    "Child": {
      "properties": {
        "a": {
          "type": "string"
         }
      }
    }
  }
}

[abdalla-rko]

I have the same issue🙁

[arthurfiorette]

Hi! Thanks for the bug report, would you want to open a PR to address this? Remember to add unit tests.