Intersection type intellisense duplicates jsdoc, rather than overriding

• VSCode Version: 1.33.1
• OS Version: macOS 10.12.6

Does this issue occur when all extensions are disabled?: Yes

Sorry if the title isn't clear, it's tricky to put into words but obvious with code. The gist is when a type is extended and has the same key, the intellisense combines the documentation, rather than the "child" overriding it, like they do with interface. It's easier to explain with an example.

When intersecting types with the same property, the intellisense documentation shows all of the comments instead of just the latest:

type Duck {
  /** This is a really great duck */
  id: string
}

type Mallard = Duck & {
  /** I love this duck */
  id: string
}

const duckMan: Mallard = {
  id   // intellisense here shows "This is a really great duck I love this duck"
}

However, with an interface, the intellisense shows only the direct type comment, which is expected.

interface Duck {
  /** This is a really great banana */
  id: string
}

interface Mallard extends Duck {
  /** I love this duck */
  id: string
}

const duckMan: Mallard = {
  id // Intellisense says "I love this duck"
}

I found this out because I'm using graphql-codegen to generate types for my GraphQL schema. It generates types, and the intellisense in some cases repeats many times.

Expectation

I would expect the "closest" comment doc of a type to override all of the others, like it does with an interface. If there's a reason that can't work, then at least having a uniqueness check would be good, maybe new Set(typedocs))

未指定源文件或测试。首先在 TypeScript IntelliSense 中复现提供的交叉类型和接口示例，然后跟踪 language-service 对交叉属性的 JSDoc 的处理；当显示最接近类型的文档且不重复继承的注释时，即视为完成。