Incremental obfuscation functionality

[aasakawa]

Since ProGuard supports incremental obfuscation by specifying -applymapping, I propose adding a functionality to incrementally obfuscate projects with multiple modules.

• root:pom
  • test1:jar
    • test.Class1
      • void method(test.Class1)
    • test.Keep1
  • test2:jar
    • test.Class2
      • void method(test.Class1)
    • test.Keep2

(An example of projects that actually work: incremental-obfuscation.zip)

In the project of the above layout, If you specify proguard_map.txt which is the result of obfuscating test1:jar with -applymapping when obfuscating test2:jar, ProGuard will consider the result of changing the identifier in test1:jar, so test.Class1 and test.Class2 will not change to the same name.

In order to support such incremental obfuscation, I introduce the following two parameters.

• File applyMappingFile (default: none)
  • If specified, specify that file as -applymapping parameter
• boolean incremental (default: false)
  • Specify whether to perform incremental obfuscation
  • In the case of true, the following behavior changes
    1. Even if applyMappingFile is specified, if the file does not exist, omit -applymapping (i.e. there is no mapping file to be applied to the originating project)
    2. If the file exists, merge the mapping file of the execution result of ProGuard into the file specified by applyMappingFile

In other words, if you set incremental = true, you will be able to obfuscate individual modules one by one in projects with multiple modules.

Note that this functionality does not work properly in versions prior to ProGuard 5.3.

Version 5.3 (Sep. 2016)

• Avoiding obfuscated name clashes with library classes.

[wvengen]

I haven't used this feature before, but the code looks fine. Thanks for adding this feature. @cmorty does this look ok to you as well?

[lasselindqvist]

@aasakawa seems good to me, but as this a somewhat complex functionality, it would benefit from good documentation, maybe an example. The explanation in this pull request is good, could it be added in some form to the site (index.apt)?

[MarcMil]

@lasselindqvist Here is a link to an example https://github.com/wvengen/proguard-maven-plugin/files/2025747/incremental-obfuscation.zip as it has been posted by @aasakawa

[lasselindqvist]

I will add the documentation later in #85