(Sketch) Convert a shape layer to a marquee. Select both bitmap and shape layer and run the plugin.

shape-layer-to-marquee.js

var document = context.document;

//	Find first bitmap and shape in selection

var bitmapLayer = document.selectedLayersOfClass(MSBitmapLayer)[0];

if(!bitmapLayer) return;

var shapeLayer = document.selectedLayersOfClass(MSShapeGroup)[0];

if(!shapeLayer) return;

//	Info

var bezierPath = shapeLayer.bezierPath().copy();
var bezierBounds = bezierPath.bounds();

var absoluteBitmapFrame = bitmapLayer.absoluteRect();
var absoluteShapeFrame = shapeLayer.absoluteRect();

//	Reset 'bounds' of bezier to 0,0

var originResetTransform = NSAffineTransform.new();

originResetTransform.translateXBy_yBy_(-bezierBounds.origin.x, -bezierBounds.origin.y);

bezierPath.transformUsingAffineTransform(originResetTransform);

//	Offset bezier so paths line up

var xDiff = absoluteShapeFrame.x() - absoluteBitmapFrame.x();
var yDiff = absoluteShapeFrame.y() - absoluteBitmapFrame.y();

var transform = NSAffineTransform.new();

transform.translateXBy_yBy_(xDiff, yDiff);

bezierPath.transformUsingAffineTransform(transform);

//	Enter edit mode for this bitmap

document.setSelectedLayers([ bitmapLayer ]); // layer list inspector does not update :(

document.actionsController().actions()["MSEditAction"].edit(null);

//	Bitmap marquee selection = shape layer's path

var currentHandler = context.document.currentHandler(); // MSBitmapEditEventHandler

currentHandler.accumulatedSelection = bezierPath;