JSDoc Does not Pick up Type imported using Require

[mjbvz]

From microsoft/vscode#20238

TypeScript Version: 2.1.6

Code

foo.js:

export class Foo {
    /**
     * @param {string} name
     * @param {number} id
     */
    constructor(name, id) {
        this.name = name;
        this.id = id
    }
}

index.js:

const {Foo} = require('./foo');

/**
 * @param {Foo} param
 */
function func(param) {

}

Expected behavior:
The type of param is Foo

Actual behavior:
The type of param is any.

If I change the import to import {Foo} from './foo', the type of param is correct

[mhegazy]

Foo is not a type. it is a constructor function. I suppose we can check if we could not look up a type, but the value points to a constructor function, use that instead.

[MicahZoltu]

@mhegazy see the repro case over in microsoft/vscode#21933 in particular, notice how to behavior is different for var foo = new Foo(). This suggests to me that the engine understands that Foo is a type (with a constructor), not just a function, but it doesn't seem to follow the same rules when told via the annotation. Perhaps I'm misunderstanding to difference between a type and a constructor function?

[MicahZoltu]

For record keeping and improving searchability of this issue, the same problem occurs with local variables, it is not limited to function parameters:

var Foo = require("./foo");

/** @type {Foo} */
var bar; // VSCode (via TypeScript engine) considers `bar` to be of type `any`

Also note that the recommended workaround of using the import syntax only applies if you are writing ES2015+, in which case you really should be using import syntax anyway. For code written in ES5 I don't believe there is any workaround to this issue.

[Zarel]

@mhegazy

Foo is not a type. it is a constructor function.

If I define Foo as a class within the file, it's a type. Why is it not a type if I import it from a different file? How do I make it a type?

I've googled this a lot and I can't find any documentation on how to make it a type. Now that TypeScript emits errors when I try to do this, I think that error is a good place to provide guidance on how to make it a type.

[mhegazy]

Based on the discussion in #15747, we want to look up the reference as a value of the look up as a type failed, and add special handling for classes.