I'm one of the developper of JD-IntelliJ a Java Decompiler plugin for IntelliJ IDEA.
Some of the users require the ability to set breakpoints in the decompiled source, see the #1 and #3 comments : http://plugins.jetbrains.com/plugin/7100?pr=idea&showAllUpdates=true
Actually I have no idea if it's possible in IntelliJ using the plugin infrastructure or if it's up to you guys to make the debugger work with decompiled sources.
In version 0.5 I was extending ContentBasedClassFileProcessor (itself extending ContentBasedFileSubstitutor), but now in version 0.6 I'm using the IntelliJ 13.1 extension point ClassFileDecompilers.Light. I supposed this new extension point will be used for a lot more than navigating decompiled source, and other stuff like quick definition, etc.
So the thing is we added realignment of the source code line of the decompiled source. But when a breakpoint is set the debugger does not use these lines and somehow only sees breakpoint as method breakpoint, and somehow it doesn't get the right code so debugger is unusable with decompiled code.
Should I provide another extension point for the debugger ? Or is it a limitation of the current infrastructure and only you guys can fix it?