JSDoc of base class/interface appears many times when using union of derived class/interface

[AnyhowStep]

TypeScript Version: 3.5.1

Search Terms:

JSDoc, duplicate, extends, implements

Code

interface InterfaceFoo<DataT extends { name : string }> {
    /**
     * Some comment
     * 
     * -----
     */
    name : DataT["name"]
}

class ClassFoo<DataT extends { name : string }> implements InterfaceFoo<DataT> {
    name! : DataT["name"]
}

///////////////////////
declare const arr2 : readonly (
    | ClassFoo<{name:"X"}>
    | ClassFoo<{name:"Y"}>
)[];
/*
Expected:
Some comment

Actual:
Some comment
-----
Some comment
-----
*/
arr2[0].name

///////////////////////
declare const arr3 : readonly (
    | ClassFoo<{name:"X"}>
    | ClassFoo<{name:"Y"}>
    | ClassFoo<{name:"Z"}>
)[];

/*
Expected:
Some comment

Actual:
Some comment
-----
Some comment
-----
Some comment
-----
*/
arr3[0].name

Expected behavior:

Some comment should only appear once

Actual behavior:

Some comment appears n times if the array contains ClassFoo<> n times

Playground Link:

Playground

Related Issues:

No idea

[AnyhowStep]

Playground

[AnyhowStep]

It seems like it has something to do with the implements/extends keyword.

Changing class ClassFoo implements to interface ClassFoo extends gives the same result,
Playground

---

Using InterfaceFoo directly is fine,
Playground

[AnyhowStep]

In my current project, I end up having a very looooooong tooltip,

You can see the scroll bar on the right side of the tooltip.

[AnyhowStep]

Shorter repro,

interface InterfaceFoo<DataT extends { name : string }> {
    /**
     * Appear only once plz
     */
    name : DataT["name"]
}

class ClassFoo<DataT extends { name : string }> implements InterfaceFoo<DataT> {
    name! : DataT["name"]
}

///////////////////////
declare const unionType : (
    | ClassFoo<{name:"X"}>
    | ClassFoo<{name:"Y"}>
);
/*
Expected:
Appear only once plz

Actual:
Appear only once plz Appear only once plz
*/
unionType.name

Playground

[Edit]

I actually like this repro more,
Playground

---

I feel like it should know that they all come from InterfaceFoo and not duplicate it.

It might make sense if the types in the union were all unrelated.

[sandersn]

Oops. We dedupe non-inherited jsdoc but forgot to do the same for inherited jsdoc.