I have an AS3 application that uses an AS3 library (which is also a separate IntelliJ project, etc), and I want to step-thru-debug this library while in use in (while running) the application. In IntelliJ 11, I could easily add the library as a module to the parent application, BUT, this doesn't seem to work as expected in IntelliJ 12...
Urrrrrr, how do you do this? This should be easy, right?
In IntelliJ 11, I could easily add the library as a module to the parent application
I'm not sure what you mean. IntelliJ IDEA modules belong to IntelliJ IDEA project, not to any 'parent application'. Anyway I'll try to answer.
1. If you are not going to edit your AS3 library code then you need to setup dependency as if it were a 3rd party library: Project Structure | Modules | [your module] | [your build configuration] | Dependencies tab. If your library is compiled into swc then you need to configure this swc as 'Classes' of IntelliJ IDEA library and add library source folder as 'Sources' correspondingly. If your library is not compiled into swc - you need to configure library sources as 'Raw AS3 Library' in IntelliJ IDEA.
2. If you are going to edit your AS3 library sources within main app project - create a separate IntelliJ IDEA module with one Flash build configuration (BC), set BC output type to Library, configure dependency of main app BC on library BC.
If I haven't answered your question please give more details about your configuration in older IntelliJ IDEA version and about the goal you want to achieve.