[Dar-libdar_api] Empty option for testing archives

[Johnathan B. <jk...@ro...>]

Hi Denis,

Is it possible to have the "empty" boolean option added to the 
libdar::archive->op_test() api? 

My plan is to use the "dummy run" option to quickly determine the number of 
files considered by an operation's selection and subtree filters, and at the 
same time in a different thread run the actual operation. Once the dummy 
operation is finished, and it returns the number of files considered, I can 
start to update my progress dialog based on the current stats of the running 
operation. The other operations have this empty option, but not the op_test.

Presumably op_test() with empty=true would traverse the archive according to 
the masks, and not perform the CRC checks.

Cheers,
JB