In JOSM, how do you draw an polygon that is adjacent to another polygon without having to retrace the shared boundary? I'm looking for the same functionality that is found in Auto-Complete Polygon tool found in Esri software: http://desktop.arcgis.com/en/arcmap/10.3/manage-data/creating-new-features/creating-adjoining-polygons.htm
What I've tried to do is draw the new polygon boundary (that doesn't have a shared boundary). Then use the Split Adjacent Ways tool. If I select the new boundary, the split boundary, and then combine them, it works but I break the other polygon. I also tried to Copy/Paste or Duplicating the split boundary, so there are two ways. I then would select the new Way to combine. But that doesn't work because the copy/paste/duplicate doesn't put the geometry in the same place.