error: This file was generated by an older version of protoc

[yurivict]

Build fails for opencv-contrib-python-4.7.0.68:

In file included from /usr/ports/graphics/py-opencv-contrib-python/work-py39/opencv-contrib-python-4.7.0.68/opencv/modules/dnn/misc/tensorflow/attr_value.pb.cc:4:
/usr/ports/graphics/py-opencv-contrib-python/work-py39/opencv-contrib-python-4.7.0.68/opencv/modules/dnn/misc/tensorflow/attr_value.pb.h:17:2: error: This file was generated by an older version of protoc which is
#error This file was generated by an older version of protoc which is
 ^

All headers generated by protobuf should be regenerated during build. They can't be reused.

[asmorkalov]

OpenCV uses own instance of Protobuf to handle ONNX, Caffe and some other DNN formats. Your error message means that you have yet another Protobuf instance in your build configuration. Please disable OpenCV DNN or use the same version everywhere.

[alalek]

Issue reports without complete reproducer are useless.

All headers generated by protobuf should be regenerated during build. They can't be reused.

BUILD_PROTOBUF=OFF (to use external version) is almost useless without UPDATE_PROTO_FILES=ON option.
There are multiple similar questions in the upstream repository.

[yurivict]

BUILD_PROTOBUF=OFF (to use external version) is almost useless without UPDATE_PROTO_FILES=ON option.

Maybe you should make this behavior default?

[yurivict]

Adding -DBUILD_PROTOBUF=ON -DUPDATE_PROTO_FILES=ON to cmake arguments in setup.py doesn't fix the error This file was generated by an older version of protoc which is

[alalek]

-DBUILD_PROTOBUF=ON -DUPDATE_PROTO_FILES=ON

Wrong usage.
The first is the default value.
The second must be OFF in that case.

Don't touch these parameters if you don't want to use system's protobuf.

We have no idea that you are doing as we don't see any reproducer.

---

Dump compiler command line with all parameters.
Add -H option to show used headers.
Ensure that there is no mess with system's protobuf headers.

[asmorkalov]

The flag was renamed. Current version uses -DPROTOBUF_UPDATE_FILES=ON. Added the case to FAQ on Wiki.