Develop Reference

How Do I Teach ProGuard to Get Rid of Something It Is Keeping That I Am Not Using?

I have an Android project with a proguard-rules.pro file for the app module that contains only the following:
# ProGuard rules
-dontobfuscate
-dontwarn android.arch.util.paging.CountedDataSource
-dontwarn android.arch.persistence.room.paging.LimitOffsetDataSource
I am not keeping anything myself. All -keep rules are coming from something else, whether that is the rules provided by getDefaultProguardFile('proguard-android-optimize.txt') or from rules packaged in libraries.
However, stuff is being kept that I am not using. If I use the Android Studio APK Analyzer on my release build, while lots of things are removed by ProGuard, lots of other things are kept that I am not referencing.
For example: through transitive dependencies, I have the Support Library module that contains ViewPager in the app's dependencies tree. However, I am not (presently) using ViewPager in this app. Despite this, something is causing it to be kept, as the APK Analyzer shows 107 defined methods for android.support.v4.view.ViewPager, including its constructor.
I could use various ProGuard options to track down why this is being kept. However, it is not coming from my rules. There is no -keep of my own that needs fixing — the -keep is coming from somebody else, presumably a Google engineer.
So, how do I get rid of ViewPager? Is there a way that I can override the -keep rule that is causing it to be kept (e.g., using allowshrinking)? If so, how does ProGuard, as invoked by Android Studio, determine whose -keep rule wins?

The ViewPager class isn't kept in a small app that I just checked, so it must be other code or other rules in your project indeed.
You can start with letting ProGuard print out the chain that triggers ViewPager to be kept:
-whyareyoukeeping class android.support.v4.view.ViewPager
You may need to repeat this a number of times for various classes and methods to get to the root cause. ProGuard doesn't print out which rule exactly is responsible -- admittedly, this would be a useful feature.
You can then look for the proguard.txt file in build/intermediates/exploded-aar that contains a matching rule.
As for a solution at that point:
It is not possible to override -keep rules; they only accumulate.
As far as I know, the Android Gradle plugin also doesn't support disabling overly conservative proguard.txt files in libraries, so you'd need to create a custom .aar file with the updated rule, or send a suggestion to the developers of the library.

Getting "unresolved references" and "can't find superclass" warnings from Proguard

I have integrated some third-party source into my android project and I'm having trouble getting it to build with proguard enabled. The build is failing with this:
Warning: there were 123 unresolved references to classes or interfaces.
You may need to add missing library jars or update their versions.
If your code works fine without the missing classes, you can suppress
the warnings with '-dontwarn' options.
(http://proguard.sourceforge.net/manual/troubleshooting.html#unresolvedclass)
Warning: there were 201 unresolved references to program class members.
Your input classes appear to be inconsistent.
You may need to recompile the code.
(http://proguard.sourceforge.net/manual/troubleshooting.html#unresolvedprogramclassmember)
Warning: Exception while processing task java.io.IOException: Please correct the above warnings first.
:app:transformClassesAndResourcesWithProguardForRelease FAILED
FAILURE: Build failed with an exception.
There are MANY notes and warnings to sort through and I can't make heads or tails of it. I have tried adding --keep class example.package.** { *; } for everything that seems to be causing warnings, but it is still failing. Can anyone suggest a strategy for dealing with issues like this? For example, if I see this:
Warning: info.guardianproject.netcipher.client.MyDefaultClientConnectionOperator: can't find superclass or interface ch.boye.httpclientandroidlib.impl.conn.DefaultClientConnectionOperator
what should I do about it?

Adding the following to your proguard-file will solve the compile problem:
-dontwarn info.guardianproject.netcipher.**
That said, you should read up on any ramifications that would come with this. Proguard is usually giving warnings for a good reason.

The reason you get those warnings is that guardianproject messed up with dependencies. As you can see here NetCipher does not have any dependencies. And httpclientandroidlib is clearly an outern project. Inside Netcipher they have built the .jar library and not packaging it into their library. Unfortunately, httpclientandroidlib is not available through jcenter dependency.
There are two solutions:
Proposed by #Tommie: add
-dontwarn info.guardianproject.netcipher.**
to you proguard-rules.pro file if those dependecies are not necessary. You just get rid of warning, sometimes it is a good way. But usually does not work. Then go to step two
You need to add httpclientandroidlib manually to your project.
Download a project from github as .zip
Add new module to your project, name it httpclientandroidlib (name is arbitrary. I name it like that just for reference)
Copy folder structure ch.boye.httpclientandroidlib to new module's src folder
Replace module's AndroidManifest with the one from httpclientandroidlib library.
Add dependecy to your main aa module:
compile project(':httpclientandroidlib')
Then you can start working with the project.

Gradle issue - You may need to add missing library jars or update their versions

When I try to generate a release version for my app I get the bellow error :
Error:Execution failed for task ':app:proguardRelease'.
java.io.IOException: Please correct the above warnings first.
Blockquote
You may need to add missing library jars or update their versions.
If your code works fine without the missing classes, you can suppress
the warnings with '-dontwarn' options.
(http://proguard.sourceforge.net/manual/troubleshooting.html#unresolvedclass)
How can I force Android Studio Gradle plugin to use -dontwarn option ?

This occurs because the release build is using Proguard. You will need to add Proguard rules in proguard-rules.pro for some of the dependencies you are using. Most libraries provide the Proguard rules needed; look on their README page.

The -dontwarn option isn't an option for Android Studio or the Android Gradle Plugin. It is a ProGuard option used to tell ProGuard not to warn you about potential problems.
From the ProGuard manual:
-dontwarn
Specifies not to warn about unresolved references and other important problems at all. The optional filter is a regular expression; ProGuard doesn't print warnings about classes with matching names. Ignoring warnings can be dangerous. For instance, if the unresolved classes or class members are indeed required for processing, the processed code will not function properly. Only use this option if you know what you're doing!
If you need to use this option, then it should go in your project-specific ProGuard file (see here if you don't know how to add your own ProGuard file).

Gradle release build with proguard: java.lang.IncompatibleClassChangeError and java.lang.NoSuchMethodError

I recently migrated a project from Eclipse/Ant to Android Studio/Gradle. I am able to successfully build a signed release version of the project with proguard enabled. However, while testing the release version, I'm getting crashes from certain library projects and jars (which work fine when building a debug version).
For example, when attempting to upload a file to Dropbox (a jar dependency), I get the following error:
java.lang.IncompatibleClassChangeError: interface not implemented
at com.dropbox.client2.session.AbstractSession.sign(SourceFile:238)
at com.dropbox.client2.DropboxAPI.putFileRequest(SourceFile:2199)
at com.dropbox.client2.DropboxAPI.putFileOverwriteRequest(SourceFile:1571)
at com.dropbox.client2.DropboxAPI.putFileOverwrite(SourceFile:1537)
Also, when attempting to sign into Box (a library project dependency), I get the following error:
java.lang.NoSuchMethodError: org.apache.http.conn.params.ConnManagerParams.setMaxTotalConnections
at com.box.restclientv2.BoxBasicRestClient.()
at com.box.boxjavalibv2.BoxRESTClient.()
at com.box.boxjavalibv2.BoxClient.createRestClient()
at com.box.boxjavalibv2.BoxClient.()
at com.box.boxandroidlibv2.BoxAndroidClient.(SourceFile:49)
at com.box.boxandroidlibv2.activities.OAuthActivity.startOAuth(SourceFile:71)
at com.box.boxandroidlibv2.activities.OAuthActivity.onCreate(SourceFile:52)
I have other jars and library projects that work just fine...
Again, there are no issues with either of these when building a gradle debug build (no proguard). I was also able to create a release build with proguard enabled using ant without any issues (able to sign into both Dropbox and Box).
Any ideas?

You appear to be including a version of the org.apache.http library. In principle, this library is already part of the Android runtime android.jar, so you shouldn't add it to your project. ProGuard is probably printing warnings about these duplicate classes.
In practice, it may be a newer version of the library, and some of your code may be using additional classes from this version. You then probably should leave the names of the classes, fields, and methods untouched, to avoid introducing (additional) conflicts:
-keep class org.apache.http.** { *; }
A build process may filter out the classes, or it may be adding the above line, but I don't think the default Android builds currently do either.

You need to -keep Proguard from removing or renaming all the class and method names that it can't determine are referenced from code that it doesn't processes, that are referenced via reflection (e.g. XML references), etc.
Keeping all apache classes may keep more than necessary (which is OK) but it may not be enough to fix all the Proguard issues.
It's good to ask why it worked from your ant build without this -keep. Maybe the ant build didn't actually call Proguard (ant is tricky), maybe it used a different Proguard data file, or maybe the relevant libraries changed in the meantime. You can debug that by listing hypotheses and testing them. E.g. if you put a malformed command in the Proguard data file then run the ant build, you can tell whether it actually runs Proguard or not.

Problems compiling an Android App with Ant and Proguard

I have an Android App which consists on different modules. The Main module is using some libs like Google's GSON or the v4.support.package. A custom build script with the right proguard.cfg will build it, too.
Now I must integrate another "Android-Library" which uses partly the same libs (GSON support.v4). Beside from getting a lot of Notes like
Note: duplicate definition of program class [com.google.gson.Gson]
I get also some Notes like
[proguard] Note: com.google.gson.UnsafeAllocator: can't find dynamically referenced class sun.misc.Unsafe
[proguard] Note: the configuration refers to the unknown class 'sun.misc.Unsafe'
that I find strange cause i have some 'keeps' in my Proguard.cfg especially for that:
-keepattributes Signature, Annotation
-keep class com.google.gson.** {*;}
-keep class sun.misc.Unsafe { *; }
which works well on my project without referencing the module-library inside it.
I'm on the Latest SDK and Tools, and added a custom proguard.cfg to the module-library, which works well on the module-lib itself (if build in standalone-mode).
It seems to me, that the build is not depending on custom proguard.cfg inside library-projects. Any idea on what to try highly appreciated

I finally found a solution for it myself:
with the last Android Tools (16), every Android-Library gets compiled on its own first.
So when the lib has not a "standart" build and defines some custom build script including proguard --keeps, and this --keeps are defined on the same Project (excluding Android SDK classes, as thei're not compiled) it leads to an proguard error.
The Solution was do remove proguard out of the lib and copy the --keeps inside the main App