Typescript: Emitted code for super() results in 'Branch not covered' in coverage reports.

[Izhaki]

TypeScript Version: 2.1.4

Code

The super() call in the following code, results in 'Branch not covered' with Istanbul (see issue).

constructor( x: number, y: number, w: number, h: number ) {
    super(); // <- Throws 'Branch not covered'.
    this.rect = new Rect( x, y, w, h);
}

In Typescript 1.8 the super() call transpiled to:

_super.call(this);

But in 2.1.4 it transpile to:

var _this = _super.call(this) || this;

Which will obviously yield 'Branch not covered'.

Adding a test - or ignore instructions - just to ensure appropriate coverage does not feel right here, let alone will have to include some comments on the internals of typescript.

[RyanCavanaugh]

This is to support subclassing classes which themselves return different objects from super

[Izhaki]

@RyanCavanaugh. OMG, had she died, Barbara would turn in her grave.

Is this in the ES6 standard? Because this looks to me like OOP on LSD.

[RyanCavanaugh]

It's a thing (tm), unfortunately

> class Tricky { constructor() { return { m: 4 } } }
[Function: Tricky]
> let t = new Tricky();
undefined
> t
{ m: 4 }
> class Mine extends Tricky { constructor() { super(); } }
[Function: Mine]
> let m = new Mine();
undefined
> m
{ m: 4 }
> m instanceof Mine
false

[DanielRosenwasser]

Also linking to https://github.com/SitePen/remap-istanbul/issues/106 in case that can fix the issue.

[Bnaya]

For the reference,
on babel, i get

(when adding to the babel config)
" auxiliaryCommentBefore: ' istanbul ignore next ',"

[mhegazy]

@Bnaya, this seems like a good feature to add. do you mind filing a new issue to track it.

[Bnaya]

I don't feel i know enough about it, i just gave the hint:)

[samvloeberghs]

@Bnaya wouldn't that ignore everything?! Seems so wrong to do :)

[Izhaki]

As mentioned in https://github.com/Microsoft/TypeScript/issues/13455#issuecomment-287900758, instead of the various workarounds proposed, it is better to simply stick to es6 when producing the coverage report. Here is an example how.

[ben8p]

For the one using webpack and TypeScript configured to output ES5,
I made a little webpack loader:
https://www.npmjs.com/package/ts-es5-istanbul-coverage
Using it make sure you won't get the branch marked as not covered.