Why start using -libraryjars when I never needed it before?

Since I updated ADT from 16 to 18 (which mandated Proguard update from 4.6 to 4.8), Proguard has been acting very weirdly (and inconsistently?).

The latest such problem is when I try to export a signed (release) APK, I receive the following errors:

Proguard returned with error code 1. See console
Warning: com.bta.LibProj2: can't find referenced class com.bta.R$string
Warning: com.bta.MyDlg1: can't find referenced class com.bta.R$string
Warning: com.bta.MyMenu: can't find referenced class com.bta.R$menu
Warning: com.bta.R: can't find referenced class com.bta.R$attr
Warning: com.bta.R: can't find referenced class com.bta.R$drawable
Warning: com.bta.R: can't find referenced class com.bta.R$menu
Warning: com.bta.R: can't find referenced class com.bta.R$string
Warning: com.bta.myapp.MyAppActivity$1: can't find referenced class com.bta.myapp.MyAppActivity
Warning: com.bta.myapp.MyAppActivity$ELicenseResponse: can't find referenced class com.bta.myapp.MyAppActivity
Warning: com.bta.myapp.MyAppActivity$MyLicenseCheckerCallback$1: can't find referenced class com.bta.myapp.MyAppActivity$MyLicenseCheckerCallback
Warning: com.bta.myapp.MyAppActivity$MyLicenseCheckerCallback$1: can't find referenced class com.bta.myapp.MyAppActivity
Warning: com.bta.myapp.R$array: can't find referenced class com.bta.myapp.R
Warning: com.bta.myapp.R$layout: can't find referenced class com.bta.myapp.R
Warning: com.bta.myapp.R$xml: can't find referenced class com.bta.myapp.R
Warning: there were 49 unresolved references to classes or interfaces.
         You may need to specify additional library jars (using '-libraryjars').
java.io.IOException: Please correct the above warnings first.
    at proguard.Initializer.execute(Initializer.java:321)
    at proguard.ProGuard.initialize(ProGuard.java:212)
    at proguard.ProGuard.execute(ProGuard.java:87)
    at proguard.ProGuard.main(ProGuard.java:493)

I did notice the recommendation to add -libraryjars in proguard.cfg, but I never needed to do this before (and I didn't change anything in my code, all I did was updating Proguard from 4.6 to 4.8). Does this suggest something wrong in my development environment configuration?

Also, I checked Proguard's Troubleshooting section for Can't find referenced class: It refers to forgetting or ignoring to specify a library via -libraryjars (which I admit), but I never specified any library and it always worked before! What changed?

My proguard.cfg file BTW starts with:

-optimizationpasses 5
-dontusemixedcaseclassnames
-dontskipnonpubliclibraryclasses
-dontpreverify
-verbose
-optimizations !code/simplification/arithmetic,!field/*,!class/merging/*

Any idea what's going on? Why did Proguard start giving me such hard time? (I coasted very smoothly with it for over a year now) Is there something fundamental I am missing in my system configuration?

BTW, I did try to add the libraries I have been using by specifying all of them in -libraryjars lines, but Proguard's behavior only got worse: It would fail without giving any of the error log that I quoted above.

Problem solved. After much search for clues here in SO, I finally found this hint by no other than Proguard's developer himself:

-dontwarn scala.**

I'm not using anything that contains "scala" and I don't know what scala is. But that gave me the idea of placing a -dontwarn on my own application package:

-dontwarn com.bta.**

That did the trick.

For the record, the search phrase that led me to finding this hint was: proguard admob "can't find referenced class".

P.S. Proguard's suggestion You may need to specify additional library jars (using '-libraryjars') wasn't even in the right direction...

UPDATE: While -dontwarn com.bta.** allowed producing a signed APK, it crashed as soon as I tried to launch it with:

ClassNotFoundException: com.bta.myapp.MyAppActivity in loader dalvik.system.PathClassLoader[/data/app/com.bta.myapp.myapp-1.apk]. 

What a nightmare.

UPDATE 2: -dontwarn com.bta.** turned out to be way too inclusive. I changed it to:

-dontwarn com.bta.myapp.MyAppActivity.R**

And now everything runs well without incident. What a nightmare.

After wasting way too much time on debugging the very tools that are supposed to save me time, I discovered the source of the problem. It's a bug in the Android SDK tools. It is documented as have been solved in r17, but I am using the latest of today (June 18 2012) and it hasn't been solved! (see comment 24). Comment 25 also describes the workaround that allows me now to proceed with my actual development.

Bugs are fact of life in complex systems. But the fact that neither Proguard nor the build tools that feed input to Proguard could provide any helpful error message (in fact they did exactly the opposite), suggests something is broken in the "methodology" of the Android development tools recommended by Google.

I had similar issues after the latest update of SDK and ADT, eventually requiring me to checkout my project from scratch. Try checking out a new copy of your project, see if that works.