Current Status

I am no longer involved in development, so am not able to maintain or provide bug fixes or even test the pull requests. It would be great if someone who actually is using this project in their library and can actively maintain the repo, become part of/take it over.

Meanwhile, you can also check fat-aar-plugin which is trying to solve the same problem using a plugin.

android-fat-aar

Gradle script that allows you to merge and embed dependencies in generated aar file.

In this Fork you can find a fixed version who will also work with embedded .aar files !

Credits

jksiezni suggested an alternate way to embed R files which fixes ugly internal proguard hack.

jonbryantnz suggested method to embed java projects.

Why do I need is a fat AAR?

There may be multiple reasons for wanting this. My reason was that I wanted to publish a single library while maintaining a modular structure within the project. The benefit of a fat aar file is that we can proguard the combined code instead of proguarding each and every subproject which is not that effective.

What doesn't work?

1. Manifest placeholders that are expected to be filled in by the application
2. AIDL File merger - I do not use aidl files
3. Multiple build types - only single build type (release) is supported out of the box
4. ?

Step 1: Apply the gradle file

To use this simply copy the gradle file 'fat-aar.gradle' to your project directory and then

apply from: 'fat-aar.gradle'

or apply directly from the url

apply from: 'https://raw.githubusercontent.com/adwiv/android-fat-aar/master/fat-aar.gradle'

Step 2: Define the embedded dependencies

Then you can modify the dependencies section and change the word compile to embedded for the dependencies you want merged within the aar file. The resulting section may look like this:

dependencies {
  compile fileTree(dir: 'libs', include: ['*.jar'])

  // Order of dependencies decide which will have precedence in case of duplicates 
  // during manifest / resource merger 
  embedded project(':librarytwo')
  embedded project(':libraryone')
  embedded project('com.example.internal:lib-three:1.2.3')
  
  compile 'com.example:some-other-lib:1.0.3'
  compile 'com.android.support:appcompat-v7:22.2.0'
}

The dependencies with keyword embedded will be merged while the others will remain referenced as before.

Step 3: Remove embedded dependencies from exported dependency list

Now that you have embedded your sub projects into the main library, you need to ensure that anyone using your library does not resolve the embedded projects as transitive dependencies. Otherwise he will get duplicate class errors.

If you are using the fat library within the same project (maybe within a test app?), then you can simply define your fat-library dependency as non transitive.

compile (project(':applibrary')) {  // Notice the parentheses around project
    transitive false
}

For external clients or use in another project; this can be achieved by removing these dependencies from the generated pom.xml file. How to automate that will depend on how you are generating the pom file. I use maven-publish plugin with the following pom generator.

pom.withXml {
    def dependenciesNode = asNode().appendNode('dependencies')
    //Iterate over the compile dependencies (we don't want the test ones), adding a <dependency> node for each
    configurations.compile.allDependencies.each {
        if(it.group != null && (it.name != null || "unspecified".equals(it.name)) && it.version != null)
        {
            if(!configurations.embedded.allDependencies.contains(it)) {
            def dependencyNode = dependenciesNode.appendNode('dependency')
            dependencyNode.appendNode('groupId', it.group)
            dependencyNode.appendNode('artifactId', it.name)
            dependencyNode.appendNode('version', it.version)
            }
        }
    }
}

The complete publish.gradle file (That also automatically adds the transitive dependencies as primary) is in the repository.

Hope this helps.