GWT supports source maps in super dev mode. Unfortunately, they seem not to work in production mode, despite the fact that I added source maps option to my *.gwt.xml file.
How to enable them there?
Have a look at how this is done for GWT's own website: https://gwt.googlesource.com/gwt-site-webapp/+/master/src/main/java/com/google/gwt/site/webapp/GWTProject.gwt.xml, specifically the includeSourceMapUrl configuration property.
Note that -saveSource is passed to the GWT compiler too.