I don't know what to say beyond the subject. I had a working project. Then I updated. Now when I compile, for every module, it complains that it can't find R.java for that project, even though it's right where it's supposed to be and always has been.
I tried changing from my custom output directory to the default .../gen. No joy.
Then I removed the module, deleted the .iml file, and recreated from scratch, using the default .../gen. That worked. But I really don't wan to have to do that for every module in every project.