[question] Protobuf versioning scheme and Protobuf_VERSION variables

[lia-viam]

What is your question?

So the versioning schemes in protobuf are a tad confusing, see eg
https://protobuf.dev/support/version-support/#cpp
In the second table, a version like C++ version 5.26.x corresponds to protoc version 26.x.

But in a homebrew install, for example, brew info protobuf reports version 26.1, and using find_package(Protobuf CONFIG) with such an install sets Protobuf_VERSION to 26.1.0. But then include/google/protobuf/port_def.inc defines

#define PROTOBUF_VERSION 5026001

corresponding to 5.26.1.

Now compare this to a conan project which requires and tool_requires, e.g., protobuf/5.27.0. The generated FindProtobuf.cmake sets set(Protobuf_VERSION "5.27.0"), but a conan create . with a CMake project which requires protobuf/5.27.0 prints

...
-- Conan: Including build module from '/Users/lia/.conan2/p/b/proto24456bb2a2261/p/lib/cmake/protobuf/protobuf-module.cmake'

and in this file protobuf-module.cmake, we have set(Protobuf_VERSION "27.0.0"), which is also what's reported from

$ ~/.conan2/p/b/proto24456bb2a2261/p/bin/protoc --version
libprotoc 27.0

Anyway long story short, is there a canonical way to extract what we might call the [lib]protoc version from the conan installation? I do think conan may be doing the more correct thing here, but I am dealing with some existing CMake code which expected to get a 20-something variable number like the one produced by homebrew. Some options I was considering would be

• invoke protoc --version within CMake
• construct a new version number from <minor>.<patch>.0 from the Protobuf_VERSION
• somehow include the protobuf-module.cmake ?
• some other option programatically within the conanfile.py ?

Any feedback/suggestions are appreciated!

[Ahajha]

Potential option is to add it as a conf_info define (see https://docs.conan.io/2/reference/conanfile/methods/package_info.html#conf-info). Then you can just read this value from the consumer conanfile.

[AbrilRBS]

Hi @lia-viam thanks a lot for your question, sorry that this got no answer till now.
A current workaround that can be implemented in the consumer conanfile, is to set the system_package_version property in your cmakedeps for protobuf, something like:

def generate(self):
    ....
    cmakedeps = CMakeDeps(self)
    cmakedeps.set_property("protobuf", "system_package_version", "20..your.desired.bit")
    cmakedeps.generate()

This will modify the config version generated for protobuf as part of your build (Note that we have conan-io/conan#17504 that would add cmake_config_version as a property for this with a better naming)

Let me know if this can help, happy to help where possible :)