Go-to-definition on tagged union property should filter down to known union case

[RikkiGibson]

TypeScript Version: 2.9.1
Issue produced using vscode 1.25.1 which appears to depend on 2.9.1

Search Terms:
tagged union, go to definition

Code

type Animal = Cat | Dog;

interface Cat {
  animaltype: "Cat",
  color: string,
  friendly: boolean;
};

interface Dog {
  animaltype: "Dog",
  color: string,
  likesToFetch: boolean;
}

const cat: Animal = {
  animaltype: "Cat",
  color: "brown",
  friendly: true
};

Expected behavior:
Go-to-definition on the color property goes to the definition on Cat instead of showing definitions for both Cat and Dog.

Actual behavior:
Go-to-definition shows candidate definitions in both the Cat and Dog interfaces.

Playground Link: https://www.typescriptlang.org/play/#src=type%20Animal%20%3D%20Cat%20%7C%20Dog%3B%0D%0A%0D%0Ainterface%20Cat%20%7B%0D%0A%20%20animaltype%3A%20%22Cat%22%2C%0D%0A%20%20color%3A%20string%2C%0D%0A%20%20friendly%3A%20boolean%3B%0D%0A%7D%0D%0A%0D%0Ainterface%20Dog%20%7B%0D%0A%20%20animaltype%3A%20%22Dog%22%2C%0D%0A%20%20color%3A%20string%2C%0D%0A%20%20likesToFetch%3A%20boolean%3B%0D%0A%7D%0D%0A%0D%0Aconst%20cat%3A%20Animal%20%3D%20%7B%0D%0A%20%20animaltype%3A%20%22Cat%22%2C%0D%0A%20%20color%3A%20%22brown%22%2C%0D%0A%20%20friendly%3A%20true%0D%0A%7D%3B

Related Issues:

[RikkiGibson]

@mhegazy @DanielRosenwasser based on our chat yesterday

[mhegazy]

QuickInfo needs to do the same as well. Assuming you have multiple jsdoc comments for color on both Dog or Cat, the compiler should be smart enough to only pick one or the other based on the discriminant property type.