Does Proguard guarantee to provide the same mapping if no source has changed?

Question

In the case, if I will

• build a project
• clean up all binaries
• build it again (no source/resources and etc has changed).

Does Proguard guarantee to provide the same mapping.txt file?

Answer 1

ProGuard is deterministic: for the same input, it will generate the same output.

There is one subtlety though: if the operating system lists input files in a directory (notably class files that are not inside an archive) in a different order, then they may be processed in a different order, and the output can be different.

Answer 2

If you want a guarantee then you have to use the mappings file as input to the obfuscation process. But then you carefully have to check all warnings about conflicts relating to that mapping file. If you ignore that, you may get subtle errors, when working with reflection.

Answer 3

It might actually happen, but i don't think proguard guarantees that.

I found this in the Proguard documentation that will allow you to reuse your mapping.txt to avoid changes on the mappings

-applymapping filename

Specifies to reuse the given name mapping that was printed out in a previous obfuscation run of ProGuard. Classes and class members that are listed in the mapping file receive the names specified along with them. Classes and class members that are not mentioned receive new names. The mapping may refer to input classes as well as library classes. This option can be useful for incremental obfuscation, i.e. processing add-ons or small patches to an existing piece of code. If the structure of the code changes fundamentally, ProGuard may print out warnings that applying a mapping is causing conflicts. You may be able to reduce this risk by specifying the option -useuniqueclassmembernames in both obfuscation runs. Only a single mapping file is allowed. Only applicable when obfuscating.