[CMake] Fix `FindGRPC.cmake` for setting up gRPC related libraries for macOS+homebrew context

[akyrtzi]

Summary

• Switch $GRPC_OPTS references to ${GRPC_OPTS}
• Also find and include the search path for abseil headers
• Only setup the gRPC related targets once, so that include(FindGRPC) can be called from multiple tools

[compnerd]

llvm/cmake/modules/FindGRPC.cmake

71

I realize that this is something that exists prior to your change, but it seems better to actually do this as target_include_directories(grpc++ PUBLIC ${GRPC_HOMEBREW_PATH}/include) which avoids the extra includes from being put into all targets.

79

Why is the header search path for all targets being modified to add abseil? Is that a dependency for some other target that is being imported here? Perhaps we should add it to that particular library and let CMake propagate it properly?

[akyrtzi]

llvm/cmake/modules/FindGRPC.cmake

71

I can give it a try, will this make the search path propagate to all the targets that depend on grpc++?

79

The gRPC headers include abseil headers.

[akyrtzi]

Use target_include_directories() to add include search paths only for the targets the depend on gRPC

[akyrtzi]

llvm/cmake/modules/FindGRPC.cmake

71

Thanks for the suggestion! Using target_include_directories() seems like a much better choice.

[compnerd]

LGTM!

llvm/cmake/modules/FindGRPC.cmake

if (HOMEBREW)
       execute_process(COMMAND ${HOMEBREW} --prefix grpc
         OUTPUT_VARIABLE GRPC_HOMEBREW_PATH
         RESULT_VARIABLE GRPC_HOMEBREW_RETURN_CODE
         OUTPUT_STRIP_TRAILING_WHITESPACE)
       execute_process(COMMAND ${HOMEBREW} --prefix protobuf
         OUTPUT_VARIABLE PROTOBUF_HOMEBREW_PATH
         RESULT_VARIABLE PROTOBUF_HOMEBREW_RETURN_CODE
         OUTPUT_STRIP_TRAILING_WHITESPACE)
+      execute_process(COMMAND ${HOMEBREW} --prefix abseil
+        OUTPUT_VARIABLE ABSL_HOMEBREW_PATH
+        RESULT_VARIABLE ABSL_HOMEBREW_RETURN_CODE
+        OUTPUT_STRIP_TRAILING_WHITESPACE)
       # If either library is not installed via Homebrew, fall back to the
       # system path.
       if (GRPC_HOMEBREW_RETURN_CODE EQUAL "0")
         include_directories(${GRPC_HOMEBREW_PATH}/include)
         list(APPEND GRPC_OPTS PATHS ${GRPC_HOMEBREW_PATH}/lib NO_DEFAULT_PATH)
       endif()
       if (PROTOBUF_HOMEBREW_RETURN_CODE EQUAL "0")
         include_directories(${PROTOBUF_HOMEBREW_PATH}/include)
         list(APPEND PROTOBUF_OPTS PATHS ${PROTOBUF_HOMEBREW_PATH}/lib NO_DEFAULT_PATH)
       endif()
+      if (ABSL_HOMEBREW_RETURN_CODE EQUAL "0")
+        include_directories(${ABSL_HOMEBREW_PATH}/include)
+      endif()
     endif()
   endif()
-  find_library(GRPC_LIBRARY grpc++ $GRPC_OPTS REQUIRED)
+  if(NOT TARGET grpc++)
+    find_library(GRPC_LIBRARY grpc++ ${GRPC_OPTS} REQUIRED)
     add_library(grpc++ UNKNOWN IMPORTED GLOBAL)
     message(STATUS "Using grpc++: " ${GRPC_LIBRARY})
     set_target_properties(grpc++ PROPERTIES IMPORTED_LOCATION ${GRPC_LIBRARY})
     if (ENABLE_GRPC_REFLECTION)
-    find_library(GRPC_REFLECTION_LIBRARY grpc++_reflection $GRPC_OPTS REQUIRED)
+      find_library(GRPC_REFLECTION_LIBRARY grpc++_reflection ${GRPC_OPTS} REQUIRED)
       add_library(grpc++_reflection UNKNOWN IMPORTED GLOBAL)
       set_target_properties(grpc++_reflection PROPERTIES IMPORTED_LOCATION ${GRPC_REFLECTION_LIBRARY})
     endif()
-  find_library(PROTOBUF_LIBRARY protobuf $PROTOBUF_OPTS REQUIRED)
+    find_library(PROTOBUF_LIBRARY protobuf ${PROTOBUF_OPTS} REQUIRED)
     message(STATUS "Using protobuf: " ${PROTOBUF_LIBRARY})
     add_library(protobuf UNKNOWN IMPORTED GLOBAL)
     set_target_properties(protobuf PROPERTIES IMPORTED_LOCATION ${PROTOBUF_LIBRARY})
   endif()
+endif()
 
 if (ENABLE_GRPC_REFLECTION)
   set(REFLECTION_LIBRARY grpc++_reflection)
 endif()
 
 # Proto headers are generated in ${CMAKE_CURRENT_BINARY_DIR}.
 # Libraries that use these headers should adjust the include path.
 # If the "GRPC" argument is given, services are also generated.