qmake provides functions for processing the contents of variables during the configuration process.
As QMAKE_FILE_NAME is a run-time and not a configuration-time variable it cannot be edited by clean_path, seems this problem cannot be solved this way, anyone any ideas?
I think I finally found a proper solution:PROTOS = interface_definitions.proto PROTOPATH = $$relative_path($$PWD, $$OUT_PWD) \
protoc is now being called this way:protoc --cpp_out=. --proto_path=. --proto_path=../project/ ../project/interface_definitions.proto
everything works fine now!