Proguard won't keep a class member's enums

Try com.stuff.MyConfigObject$MyEnum instead. The Proguard class specification expects $ as the separator for inner classes.

Actually, for what you want maybe the best option is something like this:

-keep public enum com.stuff.MyConfigObject$** {
    **[] $VALUES;
    public *;
}

This will keep only the required members for all enums nested within MyConfigObject - the required members being the $VALUES[] array (see this question for an explanation) and any public members of the enum. Any other members (e.g. private fields methods) will not be kept.

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As noted by Jesse and myself in the comments - since you are processing a library, you must also add the -keepAttributes option. From the reference guide:

For example, you should at least keep the Exceptions, InnerClasses, and Signature attributes when processing a library.

to keep all internal enums try this:

-keep class * {
    public enum **;
}

it saves me from writing every of 123 enum in proguard config.

Also, don't forget -keepAttributes if you are processing a library