* package or a module without a descriptor)
* @throws IOException
*/
protected String getSrcUrl(Object from, Object modPkgOrDecl) throws IOException {
URI fromUrl = getAbsoluteObjectUrl(from);
Module module = getModule(from);
String filename;
File folder;
if (modPkgOrDecl instanceof Element) {
Unit unit = ((Element)modPkgOrDecl).getUnit();
filename = unit.getFilename();
folder = getFolder(unit.getPackage());
} else if (modPkgOrDecl instanceof Package) {
filename = "package.ceylon";
folder = getFolder((Package)modPkgOrDecl);
} else if (modPkgOrDecl instanceof Module) {
Module moduleDecl = (Module)modPkgOrDecl;
folder = getApiOutputFolder(moduleDecl);
filename = Constants.MODULE_DESCRIPTOR;
} else {
throw new RuntimeException(CeylondMessages.msg("error.unexpected", modPkgOrDecl));
}