I have a source with a geojson with a bunch of Features of type Point.
Is it possible to draw a line through them? I've tried Layout with type line, but it produces points...
I don't want to create an additional source with the same data.
Is it possible to draw a line through them?
No. For starters, Mapbox GL JS wouldn't know in which order to draw the line.
I don't want to create an additional source with the same data.
That would be the correct solution: simply construct a new GeoJSON on the fly that uses the coordinates of each point as the coordinates of a line LineString feature. I'm not sure what your reservations are.