I encountered an issue with the type definitions for AVLayer, ShapeLayer, and TextLayer in the Types-for-Adobe . The current implementation defines both ShapeLayer and TextLayer as extends AVLayer. This causes problems when narrowing down layer types with type guards like isAVLayer, isShapeLayer, and isTextLayer.

For instance, when you try to narrow down the layer type to be either AVLayer, ShapeLayer, or TextLayer, TypeScript treats both ShapeLayer and TextLayer as subtypes of AVLayer due to inheritance. This causes the following issue: after narrowing with isAVLayer, TypeScript sees the else branch as a never type, preventing access to methods that should be available on ShapeLayer or TextLayer.

This leads to a situation where methods specific to ShapeLayer or TextLayer are inaccessible unless you use type assertions, which defeats the purpose of having separate type guards like isShapeLayer and isTextLayer.

Moreover, it is evident that AVLayer , ShapeLayer ,TextLayer are not overlapping

Here's a code example demonstrating the issue:

function isAVLayer(layer: Layer): layer is AVLayer {
    return layer instanceof AVLayer;
}

function isShapeLayer(layer: Layer): layer is ShapeLayer {
    return layer instanceof ShapeLayer;
}

function isTextLayer(layer: Layer): layer is TextLayer {
    return layer instanceof TextLayer;
}

var firstLayer = (app.project.activeItem as CompItem).selectedLayers[0];

if (isAVLayer(firstLayer) || isShapeLayer(firstLayer) || isTextLayer(firstLayer)) {
    if (isAVLayer(firstLayer)) {
        firstLayer.effect.addProperty("ADBE Gaussian Blur 2");
        alert("is AVLayer");
    } else if (isTextLayer(firstLayer)) {
        firstLayer.effect.addProperty("ADBE Gaussian Blur 2");
        alert("is TextLayer");
    } else if (isShapeLayer(firstLayer)) {
        firstLayer.effect.addProperty("ADBE Gaussian Blur 2");
        alert("is ShapeLayer");
    }
}

In this example, TypeScript incorrectly types the else branch as never, making it impossible to access methods on ShapeLayer or TextLayer unless manually type-asserted.