OpenTelemetry-cpp superbuild

[esigo]

Before opening a feature request against this repo, consider whether the feature should/could be implemented in the other OpenTelemetry client libraries. If so, please open an issue on opentelemetry-specification first.

Is your feature request related to a problem?
If so, provide a concise description of the problem.
I have a piece of cmake that builds OpenTelemetry-cpp:

ExternalProject_Add(
  opentelemetry
  DEPENDS grpc
  GIT_REPOSITORY https://github.com/open-telemetry/opentelemetry-cpp.git
  GIT_TAG v1.3.0
  GIT_SHALLOW 1
  UPDATE_COMMAND ""
  CMAKE_ARGS -DCMAKE_INSTALL_PREFIX=${STAGED_INSTALL_PREFIX}
             -DCMAKE_BUILD_TYPE=Release
             -DCMAKE_POSITION_INDEPENDENT_CODE=TRUE
             -DWITH_ZIPKIN=OFF
             -DWITH_JAEGER=OFF
             -DWITH_EXAMPLES=OFF
             -DCMAKE_INSTALL_PREFIX=/opt/third_party/install
             -DBUILD_TESTING=OFF
             -DWITH_OTLP=ON
             -DBUILD_SHARED_LIBS=ON
             -DProtobuf_DIR=${STAGED_INSTALL_PREFIX}/lib/cmake/protobuf
             -Drotobuf_DIR=${STAGED_INSTALL_PREFIX}/lib/cmake/protobuf
             -DgRPC_DIR=${grpc_DIR}
             -Dabsl_DIR=${STAGED_INSTALL_PREFIX}/lib/cmake/absl
  CMAKE_CACHE_ARGS -DCMAKE_CXX_FLAGS:STRING=${CMAKE_CXX_FLAGS}
  TEST_AFTER_INSTALL 0
  DOWNLOAD_NO_PROGRESS 1
  LOG_CONFIGURE 1
  LOG_BUILD 0
  LOG_INSTALL 1)

Where grpc is another external project (similar to #1382). The build fails using this cmake because we use find_package in module mode which doesn't find grpc/protobuf because of name mismatch. This can be solved if we use config search mode first.

failure:

  Found package configuration file:

    build/stage/lib/cmake/grpc/gRPCConfig.cmake

  but it set gRPC_FOUND to FALSE so package "gRPC" is considered to be NOT
  FOUND.  Reason given by package:

  The following imported targets are referenced, but are missing:
  protobuf::libprotobuf protobuf::libprotoc

Describe the solution you'd like
What do you want to happen instead? What is the expected behavior?
We can use this:

  find_package(Protobuf QUIET CONFIG)
  if((NOT Protobuf_FOUND AND NOT PROTOBUF_FOUND))
    find_package(Protobuf)
  endif()

Describe alternatives you've considered
Which alternative solutions or features have you considered?

Additional context
Add any other context about the feature request here.

[owent]

 find_package(Protobuf QUIET CONFIG)
 if((NOT Protobuf_FOUND AND NOT PROTOBUF_FOUND))
  find_package(Protobuf)
 endif()

I think we can search CONFIG packages first by setting CMAKE_FIND_PACKAGE_PREFER_CONFIG to ON or TRUE, not calling find_package twice.

[owent]

protobuf::libprotobuf and protobuf::libprotoc are missing only when we use legacy FindProtobuf.cmake in cmake, when using prebuilt protobuf cmake scripts with protobuf_MODULE_COMPATIBLE=ON , protobuf::libprotobuf and protobuf::libprotoc should always be available. I think we can patch the legacy FindProtobuf.cmake by adding these scripts below after find_package(Protobuf)

# For old cmake versions
foreach(NEW_VAR_NAME
  Protobuf_INCLUDE_DIR
  Protobuf_LIBRARY
  Protobuf_PROTOC_LIBRARIES
  Protobuf_LIBRARY_DEBUG
  Protobuf_PROTOC_LIBRARY_DEBUG
)
  string(TOUPPER OLD_VAR_NAME "${NEW_VAR_NAME}")
  if (NOT ${NEW_VAR_NAME} AND ${OLD_VAR_NAME})
    set(${NEW_VAR_NAME} "${${OLD_VAR_NAME}}")
  endif()
endforeach()

if(NOT TARGET protobuf::libprotobuf)
  add_library(protobuf::libprotobuf IMPORTED)

  set_target_properties(protobuf::libprotobuf PROPERTIES
    INTERFACE_INCLUDE_DIRECTORIES "${Protobuf_INCLUDE_DIR}"
    IMPORTED_LINK_INTERFACE_LANGUAGES_RELEASE "CXX;RC"
    IMPORTED_LOCATION "${Protobuf_LIBRARY$<<CONFIG:Debug>:_DEBUG}"
  )
endif()

if(NOT TARGET protobuf::libprotoc)
  add_library(protobuf::libprotoc IMPORTED)

  set_target_properties(protobuf::libprotoc PROPERTIES
    INTERFACE_INCLUDE_DIRECTORIES "${Protobuf_INCLUDE_DIR}"
    INTERFACE_LINK_LIBRARIES "protobuf::libprotobuf"
    IMPORTED_LINK_INTERFACE_LANGUAGES_RELEASE "CXX;RC"
    IMPORTED_LOCATION "${Protobuf_PROTOC_LIBRARIES$<<CONFIG:Debug>:_DEBUG}}"
  )
endif()

[esigo]

Thanks @owent, I fixed this by using another superbuild for protobuf as a dependency.
https://github.com/esigo/opentelemetry-cpp/blob/superbuild/docker/CMakeLists.txt

[compoundradius]

Following the recommendations at https://grpc.io/docs/languages/cpp/quickstart/

We strongly encourage you to install gRPC locally — using an appropriately set CMAKE_INSTALL_PREFIX — because there is no easy way to uninstall gRPC after you’ve installed it globally.

I have installed gRPC 1.50.0 to $HOME/.local.
When compiling opentelemetry-cpp with cmake -DWITH_OTLP=ON ../. I also had to patch your CMakeLists.txt to use the above recommended workaround:

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 14db63d1..f7be3c54 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -270,6 +270,10 @@ if(WITH_OTLP)
   find_package(Protobuf)
   if(WITH_OTLP_GRPC OR (NOT DEFINED WITH_OTLP_GRPC AND NOT DEFINED
                                                        CACHE{WITH_OTLP_GRPC}))
+    find_package(Protobuf QUIET CONFIG)
+    if((NOT Protobuf_FOUND AND NOT PROTOBUF_FOUND))
+        find_package(Protobuf)
+    endif()
     find_package(gRPC)
   endif()
   if((NOT Protobuf_FOUND AND NOT PROTOBUF_FOUND) OR (NOT gRPC_FOUND))

This worked, but is there a better way?