Rebuild for protobuf423

[regro-cf-autotick-bot]

This PR has been triggered in an effort to update protobuf423.

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_{This PR was created by the regro-cf-autotick-bot. The regro-cf-autotick-bot is a service to automatically track the dependency graph, migrate packages, and propose package version updates for conda-forge. Feel free to drop us a line if there are any issues! This PR was generated by https://github.com/regro/cf-scripts/actions/runs/5098316562, please use this URL for debugging.}

[conda-forge-webservices[bot]]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe) and found it was in an excellent condition.

[hmaarrfk]

@h-vetinari i'm not sure if you can help here. I've tried to force CXX 17. Am I missing something? Have we moved forward in the CXX standard?

[h-vetinari]

Am I missing something? Have we moved forward in the CXX standard?

You need to link to abseil, since protobuf now depends on it (and not just internally 😑)

$BUILD_PREFIX/ld: tf_importer.cpp:(...):undefined reference to `absl::lts_20230125::hash_internal::MixingHashState::kSeed'

On windows you need to link to the abseil_dll omnibus, whereas on unix you need to figure out in which library that symbol sits (or just try to throw all abseil links at it and see what sticks). Based on the name it's very likely absl_hash. The abseil-feedstock has a list of libraries (not guaranteed to be 100% perfect, but shouldn't be off too far)

[traversaro]

Probably to link abseil it is helpful to use find_package(Protobuf CONFIG) instead of find_package(Protobuf) ?

[hmaarrfk]

Is the current thinking that OpenCV isn't using the CMake files from Protobuf with enough precision to trigger the additional flags to get added?

[h-vetinari]

Is the current thinking that OpenCV isn't using the CMake files from Protobuf with enough precision to trigger the additional flags to get added?

I don't think most consumers of protobuf are ready for v4, and their new responsibility to (for example) link to abseil. Not even abseil's own python bindings link to abseil correctly yet. Disclaimer: I don't know where these symbols exactly are used and whose responsibility it would be to link them (protobuf or its consumers), just general observations from the migration.

[traversaro]

If you use find_package(Protobuf CONFIG), then linking with the required abseil library happens just by linking protobuf::libprotobuf or simple imported target, as those targets are imported via the protobuf-config.cmake file generated and installed by Protobuf itself. If find_package(Protobuf) is used instead, FindProtobuf.cmake is used to define protobuf::libprotobuf, ignoring the new abseil dependency. Unfortunalty find_package(Protobuf CONFIG) and find_package(Protobuf) to not offer exactly the same interface. See https://gitlab.kitware.com/cmake/cmake/-/issues/24321 for more details.

Note that FindProtobuf.cmake has other problems with new Protobuf, see https://gitlab.kitware.com/cmake/cmake/-/issues/24847 .

To give an example, this is an excerpt from protobuf-targets.cmake for libprotobuf 4.23.2 on Linux:

set_target_properties(protobuf::libprotobuf PROPERTIES
  INTERFACE_COMPILE_DEFINITIONS "PROTOBUF_USE_DLLS"
  INTERFACE_INCLUDE_DIRECTORIES "${_IMPORT_PREFIX}/include"
  INTERFACE_LINK_LIBRARIES "absl::absl_check;absl::absl_log;absl::algorithm;absl::base;absl::bind_front;absl::bits;absl::btree;absl::cleanup;absl::cord;absl::core_headers;absl::debugging;absl::die_if_null;absl::dynamic_annotations;absl::flags;absl::flat_hash_map;absl::flat_hash_set;absl::function_ref;absl::hash;absl::layout;absl::log_initialize;absl::log_severity;absl::memory;absl::node_hash_map;absl::node_hash_set;absl::optional;absl::span;absl::status;absl::statusor;absl::strings;absl::synchronization;absl::time;absl::type_traits;absl::utility;absl::variant"
)

[hmaarrfk]

Done in https://github.com/conda-forge/opencv-feedstock/pull/363

[traversaro]

Done in #363

I guess the migrator is not aware of it? Perhaps:

@conda-forge-admin, please rerun bot could

help.

[hmaarrfk]

You have to close the PR (or merge)

Sometimes it takes time