This extension generates generated_cc_atom rules, which take in exactly one C++ header or source file and list its dependencies (usually other header files). This rule type is a very thin wrapper around cc_library, mainly named this way in order to visually distinguish automatically generated rules from manually-created ones.
Generating these “atom” rules is not sufficient to make a library or executable buildable and linkable, but it should make defining cc_library, cc_test, and cc_binary rules easier, in that rule writers do not have to manually compute the dependencies and transitive dependencies.