Options subfolder

[kurddt]

This fix the following use case where both .options and .proto are located in a folder hierarchy that need to be preserved for the generated files. Some of the proto files could be imported using their path related to the proto folder

proto
├── A
│ ├── A.proto
│ ├── A.options
├── B
│ ├── B.proto
│ ├── B.options
│ ├── A.proto
│ ├── A.options
app
├── CMakeLists.txt
├── build
│ ├── A
│ │ ├── A.pb.h
│ │ ├── A.pb.c
│ ├── B
│ │ ├── B.pb.h
│ │ ├── B.pb.c
│ │ ├── A.pb.h
│ │ ├── A.pb,c

The issues where:

• It was quite hard to make sure that protoc takes the proto folder has project root and not one of the subdirectory
• When the correct folder was taken as project root the plugin could not find options files (A/A.options B/B.options) because proto/A/ and proto/B/ where added to the option file but not proto/.

[PetteriAimonen]

Is it possible that this could break builds for some of the existing users of the CMake rules?

[kurddt]

The change about the discovery of the option files won't break anything.

The modification of the order of import path might be more problematic but I think it should be OK.
The following import path have been pushed back:

• GENERATOR_PATH: This one does not contains any .proto, so not sure why it's needed by probably shouldn't be the project root
• GENERATOR_CORE_DIR: This one contains nanopb.proto so it should not be considered as the project root
• CMAKE_CURRENT_BINARY_DIR: This does not contains any .proto, o not sure why it's needed by probably shouldn't be the project root
  So no issue there.

When RELPATH is not set no logic is changed. And when set I don't see a correct use case where a user would like to have the generated NANOPB_GENERATE_CPP_APPEND_PATH before it.

[PetteriAimonen]

Sounds good to me.

The pull request currently appears marked draft. Let me know when you consider it ready for merging.

[kurddt]

I marked it ready for review, if you remember some recent contributor of the FindNanopb.cmake file it might be good to have their input on that

[PetteriAimonen]

Thanks!

I checked a few of the recent CMake contributors earlier, but they aren't particularly active on GitHub currently.
This seems straightforward enough that I just merged it directly.

The protoc include path order can be a complex things so I'll add a migration note just-in-case, even though I don't expect this to cause problems for anyone.