add build interface link to absl

Author: dbarker

CMakeLists.txt

@@ -37,6 +37,7 @@ project(opentelemetry-cpp)
 mark_as_advanced(CMAKE_TOOLCHAIN_FILE)
 
 # Prefer cmake CONFIG to auto resolve dependencies.
+# This is important to properly find protobuf versions 3.22.0 and above
 set(CMAKE_FIND_PACKAGE_PREFER_CONFIG TRUE)
 
 # Don't use customized cmake modules if vcpkg is used to resolve dependence.
@@ -418,12 +419,13 @@ endif()
 if(WITH_OTLP_GRPC
    OR WITH_OTLP_HTTP
    OR WITH_OTLP_FILE)
+   
   find_package(Protobuf)
   # Protobuf 3.22 or upper require abseil-cpp, we can find it in
   # opentelemetry-cpp-config.cmake
 
   if(WITH_OTLP_GRPC)
-    find_package(gRPC)
+    find_package(gRPC CONFIG)
   endif()
   if((NOT Protobuf_FOUND AND NOT PROTOBUF_FOUND) OR (WITH_OTLP_GRPC
                                                      AND NOT gRPC_FOUND))
@@ -442,7 +444,7 @@ if(WITH_OTLP_GRPC
       find_package(Protobuf REQUIRED)
     endif()
     if(NOT gRPC_FOUND AND WITH_OTLP_GRPC)
-      find_package(gRPC)
+      find_package(gRPC CONFIG)
     endif()
     if(WIN32)
       # Always use x64 protoc.exe

cmake/opentelemetry-proto.cmake

@@ -397,6 +397,14 @@ else() # cmake 3.8 or lower
   target_link_libraries(opentelemetry_proto PUBLIC ${Protobuf_LIBRARIES})
 endif()
 
+# this is needed on some older grcp versions specifically conan recipe for grpc/1.54.3
+if(WITH_OTLP_GRPC)
+  if(TARGET absl::synchronization)
+    target_link_libraries(opentelemetry_proto_grpc
+                          PUBLIC "$<BUILD_INTERFACE:absl::synchronization>")
+  endif()
+endif()
+
 if(BUILD_SHARED_LIBS)
   foreach(proto_target ${OPENTELEMETRY_PROTO_TARGETS})
     set_property(TARGET ${proto_target} PROPERTY POSITION_INDEPENDENT_CODE ON)